Category Archives: Digital Recording Platforms

Description of different hardware platforms that can be used to record Archaeology and Cultural Heritage

Using existing mapping data to control UAV mapping flights – Part 1 – Preliminary Ideas and Experimentation

An intrinsic problem with photogrammetry is its requirement to keep the camera facing the subject matter. A much higher quality and more accurate 3D model is produced using the method than taking photographs at an oblique angle. This is especially true of buildings with with flat facades, (this has already been discussed in another blog).

Work has been done using computer vision to automate the control of the camera position so that it follows targets selected by the pilot. Although this has potential for some recording methods such as site tours, as discussed in another blog, it doesn’t aid in the recording of complex topography or architecture. Although there is potential for the recording of architectural elements using computer vision  technologies (this will be discussed in a later blog).

Other work is being done in using a low detail 3D model of a building to aid in the control of a UAV flying around it, but these are more aimed at collision avoidance than quality recording.

While in the future i plan to look at the potential pre-scanning a building with an aerial LiDAR scanner mounted on a drone before recording with UAV.

Potential solution

The camera gimbal of a UAV can be controlled both remotely and from the autopilot of the UAV which could be used to always keep the camera facing the subject matter, but without pertinent information this would have to be done manually. With wireless camera technology it is possible to remotely view what the camera is recording and so control the movement of the gimbal when required, but this would require a second person to control the camera while the UAV is being flown and would be difficult to implement effectively and costly in a commercial environment.

But it would seem to be possible to use existing 3D data of an area to control the flight of a UAV; both controlling the altitude and the angle that the camera gimbal is pointing. I have already discussed the use of DroneKit Python to create a UAV mapping flight, thish can also be used to control the angle of the camera gimbal.

Existing Data

There are a number of existing sources of data that can be used to aid in creating a mapping flight.

Within the UK LiDAR data is freely available at different spatial resolutions, much of the country is available down to 1m while other areas are available down to 0.25 m.

This resource through processing in GIS (Geographic Information System) software provides all of the information required to create a flight path over the area under study and to control the angle of the camera gimbal so that it will record it to a higher quality than before.

A digital elevation model (DEM) created using photogrammetry from existing overlapping aerial photographs can also be employed once it is georeferenced to its correct location. This resource may provide a higher spatial resolution than the LiDAR data and so a better resource for the creation of the flight path, but the landscape and structures may have changed since the photographs were taken causing problems (this can of course be a problem with the LiDAR data as well).

Co-ordinate system problems

One complication with using LiDAR data to control the UAV is the fact that it is in a different co-ordinate system than the GPS of the UAV (OSGB and WGS84). This can be solved be translating one set of data to the co-ordinate system of the other. As the number of points for the mission path will be a lot less than that for the LiDAR data it would make sense to convert the GPS data to OSGB, but this also requires that it be converted back after the flight path has been created added a certain amount of inaccuracy into the data as a conversion is never 100% accurate.

required Data

Three different pieces of data need to be derived from the LiDAR data which are required for the UAV mapping flight:

  • Altitude.
  • Slope.
  • Aspect.

The Altitude is contained within each point of the LiDAR data and is used when displaying the data in GIS software.

The Slope of the topography/buildings is measure in increments up to 90 degrees, with o degrees being flat and 90 degrees being a vertical face.

The Aspect is which way any slope is pointing in is measured in increments from 1-360 degrees. (degrees).

 

Slope_angles

Slope angles

Although it would be possible to create software that extracts the data from the LiDAR file while creating a flight path this is not currently an option. The flight path is currently created in a piece of software such as the Open Source ‘Mission Planner’ system. In this an area is chosen together with other variables and an optimal flight path is created. This flight path file can then be saved, it contains the X and Y co-ordinates of each point of the mission.

UAV Control

At its simplest the flight path can be created with the altitude and slope derived from the LiDAR being used to control both the UAV altitude and camera gimbal angle. This would work well for sloping topography but would be more complicated for areas with sharp breaks in slope (such as buildings).

Altitude Control

The altitude will need to be carefully controlled to make sure that the quality of the imaginary is consistent across the whole area under study. At its simplest this is easy to do using the altitude data within the LiDAR data, together with obstacle avoidance sensors to aid with safety.

The problem arises when needing to record something near or completely vertical. Rather than requiring a set altitude the UAV needs to maintain a set distance horizontally. This may be possible by creating a buffer in the data around steeply sloping areas.

Drone_flight_path

Problem with vertical offset

Camera Gimbal Control

Most low cost UAV systems come with a 2-axis gimbals, this means that the camera is stabilized so that it always stays in a horizontal plane but also that its rotation can be controlled downwards.

Gimbal_angle

The angle of the gimbal begins at 0 degrees for a forward pointing position to 90 degrees for a downwards facing position. This is how is its controlled within DroneKit.

As seen earlier the slope is calculated between 0 and 90 degrees for a slope.

There are two intrinsic problems with this method:

  1. The slope only goes between 0 and 90 degrees so there is no aspect data within it. If the drone camera is to be controlled to record the building as it flies over if needs to know which way the building is pointing as the 45 degrees on the left is not the same as the 45 degrees on the right. This could be solved by combining the information from the slope and aspect to give more detailed resulting data.
  2. Most standard gimbals are designed to only point forwards and downwards. This means that the UAV has to turn around to record the back side of the building or it needs to fly the path in reverse. The other solution is to use a UAV with a camera that can point in 360 degrees.

GIS Processing

A certain amount of processing is required within GIS software to get the required data from the LiDAR data and combine it with the required mapping flight path. For this ArcGIS has been used both due to its availability at university and my own familiarity with it.

Lidar

Considering the LiDAR data is for a specific square it makes sense to use raster data rather than the points and lines of vector data as it retains the accuracy of the data. The LiDAR data can be simply loaded into the GIS software as a raster.

Within GIS software the Aspect and Slope can be calculated and a raster created showing the results.

This can be done using the Spatial Analyst or 3D Analyst Toolboxes to provide Slope and Aspect rasters.

The data for these can be incorporated into Attribute Tables which can be exported into text files. It is possible to combine all of the data into one attribute table containing the Altitude, Slope and Aspect.

Although it is possible to export this whole raster file including all of the data it is not currently possible to automatically derive the data in software using the flight path, so a flight path has to be loaded into the GIS software.

Flight Path

The flight path file we created in the Mission Planner software needs to be loaded into a feature class in the GIS software. This can be done by loading the point data for the flight path into the software, this is the beginning and end point for each of the back and forth paths across the area needed to be recorded.

We next need to recreate the flight path using ‘point to line’.

Even though we have recreated the lines, deriving enough data from them is not possible as the flight path is designed to fly back and forth at a set altitude. For this reason we need to create a number of extra points. This can be done using ‘Construct points’ where points can be created at set intervals along a line. This can be linked to the level of data that is being used, so for this LiDAR data the points can be set at intervals of 1m.

Once this his has been done ‘Extract multi-values to points’ can be run on the 3 sets of data to create a table containing all of the required data for each point on the flight path we have created.

UAV Mission Creation

Now that we have all of the required input data for the UAV mapping flight we need to create the mission within Dronekit Python.

For the first level of experimentation we can just load the point data file into python then create a number of points for the UAV to fly to which give the X and Y co-ordinates and the required altitude. At the same time we can also program in the angle for the camera gimbal. It may be best to have the UAV hover at the positions for a second or two so that we know how the recording is going.

As already mentioned if we are only using a 2-axis gimbal we are going to have to have the UAV turn through 180 degrees to record the back sides of buildings and slopes sloping away from the camera. We should be able to do this by altering the UAV Yaw. We will need to have the Python read the aspect angle and change how it creates the flight path depending on the aspect of the slope/building.

Future Directions

ArcGIS allows the use of Python to run tools in its toolbox so it seems possible to create a python script which would automatically create a file with all of the information required from input files of LiDAR data and a flight path.

As QGIS also allows the use of python it would also seem possible to create the required file within this open-source solution.

 

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UAV Building Facade Recording – Part 1 – Preliminary Ideas and Experimentation

The recording of buildings is an important area in Cultural Heritage, whether for conditional surveys or to record something that is about to be destroyed.

Traditional methods rely upon survey equipment such as Total Stations to take a number of points on the façade, but this results in only points and lines with no great surface detail.

Other more detailed survey techniques such as laser scanning and photogrammetry have also been employed. But laser scanning is expensive and both the techniques are generally ground based missing detail of the façade that is not visible from this position. Scaffolding or a cherry picker can be used to record the whole of the building but again this can add to the cost the recording.

Photogrammetry is a low cost method of producing high quality results but relies upon having the camera parallel to the building to produce the best results, as capturing photographs from an angle brings inaccuracies into the recording as well as there being more detail at the bottom of the 3D model created than at the top.

The UAV would seem to provide an ideal platform to carry a camera parallel to the building, recording photographs with the required photogrammetry overlap. And with its autopilot it would seem possible to automate the recording process allowing the mapping of the façade in the same way that the UAV  can map the ground.

There are of course a number of problems that need to be overcome.

Building Façade Recording

Manual

Building façade recording can be done manually with a UAV, but the larger and more complicated the building façade the mode difficult it is to do this accurately. As the pilot needs to control the UAV accurately in 3 dimensions as well as controlling its speed.

Although the results for an experimental UAV mission are acceptable the difficulty of maintaining a manual position can be seen in the image below.

Automatic

In order to automate the process you need to determine what parameters are required to record a building façade using photogrammetry.

These can be seen below.

Excel Calculations

Building facade recording parameters

First experimentation was done by taking the co-ordinates of the two ends of an example the wall from Google Earth (The south facing wall of the lay brothers’ quarters at Waverley Abbey in Surrey was used). These co-ordinates can then be used to determine the bearing that the wall lies upon and its width. Using the camera parameters and level of detail the required distance from the wall for the flight can be calculated using trigonometry. Trigonometry is once again used to calculate the offset positions for the left and right extent of the flight.

 

The image overlap can be used to determine the number of photographs required in the horizontal and vertical, and hence the change of altitude that is required for each flight pass of the building.

Calculate altitude changes

Calculate altitude

Although it is planned to have the ability for the UAV to hover and take photographs, it is much easier to have it take photographs as it flies across the building façade. This requires the additional calculations and control of optimum flight speed and shutter speed to take photographs which are not adversely effected by motion blur.

Shutter speed formula

Shutter speed formula

Shutter speed calculions

Shutter speed calculations

These preliminary calculations were done in Microsoft Excel.

DroneKit

The drone manufacturer 3DR provides a series of software development kits (SDKs) for writing applications to control your UAV using one of the open-source autopilot systems they support.

DroneKit Python uses the Python programming language and provides a number of examples to help with programming the flight of a UAV; these include flying from co-ordinate to co-ordinate up to complete missions. Together with this there is an API (application program interface) reference which provides all of the Python commands that can be used to control the UAV.

Python

Python is a fairly easy to learn programming language and as DroneKit already requires it to be installed and setup it makes sense to use the same language to calcuate the required paramaters for the flight path. This was done with the aid of a number of online resources. A graphical user interface (GUI) was created using the Tkinter Python package and was used to enter the data. The python code did the calculations then a file is exported which combines these calculations with the DroneKit code for controlling the autopilot. The final file when run will control the UAV flight.

Python GUI

Python GUI

Virtual Drone

Experimentation doesn’t need to be done with a live UAV, it can actually be done with a virtual one using a number of pieces of open-source software. These include Mission  Planner, ArduCopterMAVProxy and SITL (Software in the loop)

Virtual Drone

Virtual Drone

Next Steps

Experimentation with a UAV using the hardware and software is the next step to test whether a GPS can be used in close proximity to a structure.

Limitations of standard UAV GPS accuracy to within the range of meters also complicates the use of this method of controlling the flight. This either needs to be solved with the use of a more accurate GPS (although the proximity to the building may block the signal), sensors that measure distances or the use of computer vision technologies to control the UAV position. The UAV afterall currently only need to fly between two set points then at set altitudes above the ground.

DJI Phantom 4

The DJI Phantom 4 is the new model in the popular phantom range of quadcopters, it has a number of improvements over previous models.

DJI Phantom 4

DJI Phantom 4

Comparison of DJI Phantom 4 and 3

Model Phantom 4 Aircraft Phantom 3 Professional or Advanced Aircraft
Battery 4S 15.2V 5350mAh Intelligent Flight Battery 4S 15.2V 4480mAh Intelligent Flight Battery
Max Flight Time 28 mins About 23 mins
Vision Positioning System 10m 3m
Obstacle Sensing System Optical Sensor – 0.7 – 15m N/A
Intelligent Flight Modes Follow Me
Point of Interest
Waypoints
Course Lock
Home Lock
ActiveTrack
TapFly
Follow Me
Point of Interest
Waypoints
Course Lock
Home Lock

Using the TapFly mode you can tap on a position of the screen in the app to fly to that location.

One of its main improvements is the introduction of obstacle avoidance technology (Sense and Avoid) using cameras mounted above the legs on the front of the Phantom 4.
DJI Phantom 4 - Obstacle Avoidance

DJI Phantom 4 – Obstacle Avoidance

The system, and the subsequent technologies, rely on a companion computer within the drone attached to the various sensors which uses computer vision algorithms to detect obstacles in the drones path. Once it has detected an obstacle it will either hover or fly around it.

DJI Phantom 4 - Companion Computer

DJI Phantom 4 – Companion Computer

It also comes with an improved Vision Positioning System, for position hold without the aid of GPS, which raises the positioning altitude from 3m to up to 10m.

DJI Phanton 4 - Vision Positioning

DJI Phanton 4 – Vision Positioning

A final important new technology is ActiveTrack where a subject can be selected in the app, and once again using computer vision technologies, the Phantom 4 will follow the subject even when it is turning.

DJI Phantom 4 - Active Track

DJI Phantom 4 – Active Track

The DJI Phantom 4 is available for £1,229.00 and will be on general release from the 23rd of March. As such it will be the first commercially available drone with obstacle avoidance technology.

Benefits

The Phantom 4 provides a number of cutting edge technologies on a low cost platform. The benefit of ActiveTrack has already been discussed in a previous blog – UAVs for site tour recording – Part 1 – Theory while the potential of the sense and avoid and vision positioning system technologies will be discussed in a future blog on building recording.

Drawbacks

The main drawback of the system is the fact that the camera is not of the same quality as the Zenmsue X5 which is available for the DJ Inspire 1 Pro/Raw. But even this camera is not of the same specifications as many standard DSLR or mirrorless cameras, only providing 16MP.

3D Printing and the UAV

3D printing provides a cheap method of creating objects from 3D computer model files. This, together with recent development in the field, have great potential for the future of the Unmanned Aerial Vehicle (UAV) industry.

3D Printing Parts
Many ready built UAVs can be purchased off the shelf configured to work with a number of different cameras building, but DIY systems can require parts that are not available from traditional sources. This is where the Maker community can come in, whether providing 3D models on such sites as Thingiverse to be 3D printed yourself or at a number of 3D printing shops; or providing ready 3D printed objects over the internet.

Among the objects that are useful to be 3D printed for UAVs are camera specific mounts and mounts for radio antennas. Complete 3D printed UAV frames are also possible.

Recent Developments
Until recently the materials that could be printed were limited, namely only thermoplastics or UV resins for the UAV body, recent developments have allowed the printing of everything from metal to human tissue and organs and even food; opening up whole new potential areas of use.

One example is the research by Dr. Jennifer A. Lewis, a founder of the Voxel8 company and Harvard University professor, which has led to 3D printers being able to print circuits such as the Voxel8 3D Printer developed by her company.

Conductive Ink Printing

Conductive Ink Printing

The Voxel8 3D Printer ships towards the end of the year.

Future developments planned by Voxel8 include the development of inks that are capable of printing resistors, sensors and even lithium ion battery cells.

In collaboration with Autodesk they have developed the Project Wire software which allows everything from design through to machine control of electrical circuits.

Autodesk Project Wire

Autodesk Project Wire

Potential
3D Printers have already been used for printing UAV components, but these recent developments open up the possibility of 3D printing almost complete UAVs in the near future. This would allow for UAVs specific to a task to be designed and printed on demand without the requirement of expensive manufacturing practices.

It would also link in with the idea of drones owning themselves, discussed in a previous blog, with the drones being able to print replacement or upgrade components straight from a 3D printer.

Brushless Gimbals – Part 1 – Introduction

Camera Gimbals
Camera Gimbals are used for many different things in many different industries including stabilizing cameras for TV/Cinema. Their development can be traced from the introduction of the Steadicam in the 1970’s. This allowed the stabilized movement of a camera, revolutionizing filming by removing the need for a wheeled Camera Dolly running on expensive/time consuming tracks or leveled boards. Although the system is not motorized it introduced the principal of a stabilized camera.

Recent technological developments have allowed the construction of lightweight/low cost motorized gimbal systems which can be carried by UAVs.

Gimbals and Archaeological/Heritage recording
With the development of the UAV the development of a lightweight camera gimbal to enable it to carry stabilized cameras was also begun.

The gimbal has become an important element in UAV photographic/video recording, from taking vertical photographs for mapping purposes to cinematic style flypasts/throughs of buildings.

Mapping can be undertaken with cameras attached to the UAV with a static mount, but this removes the ability to use the camera for other recording methods without landing the UAV and changing the mount.

3D Printed UAV Mapping Mount

3D Printed UAV Downward Facing Mapping Mount

Although this series of blogs will concentrate on UAV camera gimbals,  much of what is discussed is transferable to other recording platforms/techniques.

There are also other recording systems that use gimbals which could aid in recording; including handheld GoPro systems such as the EasyGimbal Kickstarter Project.

EasyGimbal handheld GoPro Gimabl

EasyGimbal handheld GoPro Gimbal

Some of these types of systems, such as the FY G4 handheld gimbal, can be attached to extensions poles allowing low altitude aerial photography/video to be undertaken using a handheld remote control to rotate the gimbal.

FY Reach extension pole with FY G4 3-xis handheld gimbal

FY Reach extension pole with FY G4 3-xis handheld gimbal

Gimbals can also provide a stabilized camera platform on rovers such as the Flyoxis Buggy Cam allowing the recording of ceilings and tunnels.

Flyonix Buggy Cam

UAV camera gimbals

UAV camera gimbals are designed to:

1. Remove camera vibration using the anti-vibration rubber balls within the gimbal frame.
2. Stabilize the camera as the UAV moves, keeping it level and pointing in the required direction.
3. Allow the movement of the camera to point at the subject matter while flying the UAV, sometimes in completely different directions.

Types of gimbal

Gimbals come in two different types:

1. The two-axis gimbal.
2. The three-axis gimbal.

Two-axis gimbals are designed for UAVs where there is no requirement to pan the camera from left to right, such as those with fixed landing gear which precludes the panning of cameras whether physically or visually.

Zenmuse H3-2D 2-Axiz Gimbal on a DJI Phantom 2

There are many different gimbals for numbers of different camera, from GoPros through mirrorless cameras to Digital SLR cameras.

Some of these can be purchased already constructed and calibrated out of the box, such as the Zenmuse Gimbals supplied by DJI Innovations. Others come ready installed on a UAV. While the one I will be discussing is a DIY kit which needs to be built and setup.

The price difference between buying a ready made solution and building your own one from a kit in order to carry the same camera can can be quite significant:

Model Camera Price
DYS BLG3SN 3-Axis Brushless Gimbal with BaseCam SimpleBGC 32-bit controller Sony NEX size camera £299.94
Zenmuse Z15 Sony NEX 5 and 7 £1,915.00

Components
The brushless gimbal is made up of a number of different components:

  • Gimbal frame
  • Gimbal controller
  • IMU (Inertial Measurement Units)
  • Brushless Motors
  • Battery
  • Camera
Gimbal Frame

Gimbal frames are deigned for different types of cameras. The gimbal frame I am using for this project is the DYS BLG3SN 3-Axis Brushless Gimbal Frame kit with 3pcs BGM4108-130 Brushless Motors for the SONY NEX type of camera. I will be using a Sony α5000 Mirrorless Camera which is almost identical to the NEX series cameras.

DSC00792

DYS 3 Axis Brushless Gimbal

Gimbal Controller

In order to control the gimbal a gimbal controller board is required, there are a number available on the market. The Zenmuse gimbals supplied by DJI Innovations are designed to connect directly into the DJI UAV, while other  solutions require a separate board.

The gimbal controller board one I am using is the BaseCam SimpleBGC 32-bit board which is designed for 3-axis gimbals. The cheaper and simpler BaseCam (AlexMos) SimpleBGC (formerly called AlexMos) although designed for 2-axis gimbals can be upgraded to support 3-axis gimbals with the addition of an extension board. The 32-bit board is a lot easier to use as well as being more up-to-date and so was chosen as a first gimbal construction experiment.

Basecam SimpleBGC 32 Bit Gimbal Controller with IMU attached

IMU (Inertial Measurement Unit)

Another important element is the IMU , in the case of this 3-axis gimbal two of these are required. One is connected to the main frame of the camera gimbal while the other is connected to the camera mount. These tell the gimbal controller which direction the gimbal/camera is pointing and the gimbal controller can then control the motors to point the camera in the required direction.

IMU attached to gimbal frame

Brushless Motors

The importance of brushless motors in the development of lightweight/high-powered UAV systems has already been discussed in another blog.

Those in gimbals are slightly different, rather than being designed to spin quickly they are designed to hold the camera in position with enough torque to stop it moving and also to rotate to level the camera when required.

In the case of a 3-axis gimbal one motor is required for each of the 3 axis.

DSC00798

Brushless Gimbal motor

Although originally it was required to rewind the wires inside motors designed for the rotor blade with thinner wires to increase the motor resistance and torque, it is now possible to buy ready made motors for the purpose. These motors come in different sizes depending on the size of the camera they are required to stabilize.

Calibration
In order to use the gimbal it needs to be calibrated. This is done using the OpenSource SimpleBCG program. The is installed either as a Windows program or Android app and the gimbal is calibrated using the USB port on the gimbal controller board.

Detailed instructions on how to do this can be found in many places including YouTube videos.

In the case of a 3-axis gimbal two IMUs need to be calibrated, one for the camera and the other for the gimbal frame.

SimpleBCG Gimbal Calibration Software

A triple axis camera spirit level can be used to accurately calibrate the two IMUs.

DSC00918

Camera Triple Axis Spirit Level

A number of other settings can be altered in order that the gimbal works as required.

3 Axis Brushless Gimbal for Sony NEX size cameras

3 Axis Brushless Gimbal for Sony NEX size cameras

Once the gimbal controller has been calibrated the camera will remain in place as the gimbal is moved around it. This is done by calibrating the IMUs to a nominal position, the IMUs determine the actual position of the gimbal and the motors are turned on to correct the position, less voltage is sent to the motors the closer to the nominal position that the gimbal is.

Sources
http://www.simplebgc.com/eng/

http://www.simplebgc.org/

http://www.unmannedtechshop.co.uk/3-axis-brushless-gimbal-sony-nex-size-camera/

http://www.unmannedtech.co.uk/manualsguides/blg3sn-brushless-gimbal-assembly-guide

http://www.dronetrest.com/t/how-to-connect-and-setup-alexmos-3-axis-brushless-gimbal-controller/53

http://www.dronetrest.com/t/balancing-your-brushless-gimbal/55

https://en.wikipedia.org/wiki/Gimbal

Mirror-less Cameras and UAVs

UAV (Unmanned Aerial Vehicle) photography and photogrammetry has long been a balance between weight and the quality of the camera equipment carried.

Cameras

Low cost camera solutions such as the GoPro can be carried on almost all UAVs because they are small and lightweight, but these benefits are also drawbacks because limited size/fish eye lenses and small image sensors reduce the quality of the photographs they take, together with this the lack of control of many of the camera settings is a drawback.

High quality DSLR (Digital Single Lens Reflex) cameras have superior quality lenses and image sensors together with the fact that they have extensive control of the camera settings meaning that they take much better photographs. But they can only be carried by much higher power/cost octo and hexo-copter systems.

One solution is the lightweight point-and-shoot camera/compact camera used in some mapping solutions, such as those provided by 3DRobotics (Canon PowerShot S100). Although these cameras provide a better quality solution than the GoPro, and may be all that is required for mapping exercises; they are still limited in their optics and higher megapixel sensors which are much more important in the recording of complicated structures and photogrammetry work.

Changes in the camera industry due to competition from the phone industry has enhanced development of a different solution. This is the MILC (Mirrorless Interchangeable-lens camera) or DSLM (Digital Single Lens Mirrorless) Camera. These cameras don’t have the mirror reflex optical viewfinder of a DSLR camera, and the associated weight, replacing it with a LCD screen or with an app on a mobile device which controls the camera. As a result they have the capability to carry high quality interchangeable lenses without the weight associated with DSLR cameras. The system comes in two different forms; the first resembles a standard digital SLR camera, while the second resembles just a lens with all control being provided by an app on a mobile device.

Camera Comparison
Camera Type Megapixel Weight Cost
Canon EOS 5D Mark III Digital SLR 22.3 Approx 950g £2,544
Nikon D5300 Digital SLR 24.2 Approx 840g £549.99
Sony A5000 DSLM Digital SLM 20.1 Approx 388g £250
Sony ILCE-QX1 Lens Style Camera 20.1 Approx 332g £250
Canon PowerShot S100 Compact Camera 12.1 Approx 198g £195
GoPro Hero3+ Black Sports Camera 12 74/136g (with housing) £349.99
Canon EOS 5D Mark III

Canon EOS 5D Mark III

Nikon D5300

Nikon D5300

α5000 E-mount Camera

α5000 E-mount Camera

ILCE-QX1 Lens-Style Camera

ILCE-QX1 Lens-Style Camera

3DRobotics UAV Mapping Solutions, discussed in another blog entry, carry the Canon PowerShot S100 digital compact camera.

Canon PowerShot S100

Canon PowerShot S100

GoPro Hero3+ Black

GoPro Hero3+ Black

UAVs

UAVs come in a number of different configurations and increase in price with a higher level of complexity and ability to carry heavier loads.

UAV Comparison
UAV Type Payload Capacity Price (Without Gimbal)
3D Robotics Iris+ Quadcopter 400g £599
3D Robotics X8+ Octocopter 800g – 1Kg with reduced flight time £880
Spreading Wings S900 Hexacopter 4.7 – 8.2Kg £1,291-£1,540
DJI Spreading Wings S1000+ Octocopter 11Kg £1,750-£2,057
3D Robotics Iris+ Quadcopter

3D Robotics Iris+ Quadcopter

3D Robotics X8+ octocopter

3D Robotics X8+ Octocopter

Gimbals

Gimabls are an important element in stabilizing cameras during photography and video recording, as well as providing a motorized solution to move the camera to a desired angle during flight. They can add significantly to both the weight and price of any UAV solution depending on the camera equipment they are carrying.

Gimbal Price Comparison
Gimbal Camera Weight (Camera excluded) Cost
DJI Zenmuse H4-3D GoPro 168g £249
DYS 3 axis brushless gimbal Sony NEX size camera 388g £231.95 – £299.94
DJI Zenmuse Z15-A7 Sony α7s and α7r 1.3Kg £1,915
DJI Zenmuse Z15-5D III (HD) Canon EOS 5D DSLR 1.53Kg £2,831

Solutions

The 3DRobotics Iris+ Quadcopter has a payload capacity of 400g which would allow a rather small 15g for a mount to attach a Sony A5000 DSLM or 68g to attach a Sony QX1 Lens-Style Camera without weighing too much, although the system could be flown with excess weight reducing the flight time. A downward facing 3D Printed Sony A5000 Mapping Mount  is available for both the Iris+ Quadcopter and X8+ Octocopter, it weighs 36g.

Although the X8+ is a octocopter by definition, it gets over the intrinsic problems of size, weight and cost caused by eight separate arms by having two rotors on each arm, one pointing up and the other downwards. With a maximum payload of 1KG it can carry a Sony A5000 DSLM camera (388g) together with a gimbal such as the DYS 3 Axis Brushless Gimbal for Sony NEX size cameras (609g) to support and move it, the gimbal is designed for the NEX range of cameras, but they are almost identical to the A5000 in design. Although a lighter mount could be used.

3 Axis Brushless Gimbal for Sony NEX size cameras

3 Axis Brushless Gimbal for Sony Nex size cameras

Conclusions

The mirror-less camera would seem to provide a solution to the problem of how to carry a high specification camera capable of capturing high quality images on a fairly low-cost UAV solution.

Sources

http://en.wikipedia.org/wiki/Mirrorless_interchangeable-lens_camera

http://www.dummies.com/how-to/content/gopro-cameras-understand-the-cameras-limitations.html

http://www.japantimes.co.jp/news/2013/12/30/business/mirrorless-cameras-offer-glimmer-of-hope-to-makers/

Quadcopter vs Hexacopter vs Octocopter: The Pros and Cons

UAV (Unmanned Aerial Vehicle) Archaeological and Cultural Heritage Recording

Introduction

Recent developments in a number of technical areas has allowed the development of battery powered UAV (Unmanned Aerial Vehicles) systems which has allowed recording technologies to become airborne easily with extensive control over what is being recorded.

Many of these low cost UAV solution come ready to fly out of the box with some even coming with a camera. These systems have allowed archaeology and cultural heritage to be recorded in whole new innovative ways.

There are basically two types of UAV systems that are employed, each with their benefits and drawbacks:

  • Fixed wing systems use less power and can spend longer flying, but don’t have the ability to hover in one place or change direction quickly. They are also designed for mapping so carry cameras that only point downwards.
    The 3DRobitics Aero-M fixed-wing drone

    The 3DRobitics Aero-M fixed-wing drone

  • Multi-rotor systems use more power as their multiple rotors are turning all of the time they are in the air, so they can spend less time flying and recording. They have the ability to hover and change direction and altitude quickly.
    X8-M

    The 3DRobotics X8-M hexacopter

Recent developments have seen UAVs which combine the two systems, such as the SkyProwler Kickstarter Project. This is a system that can be fixed wing, fixed wing with rotors or just rotors. The rotors are retractable which can be deployed when required while in the fixed wing configuration.

Krossblade SkyProwler

Krossblade SkyProwler

UAV Technological developments

A number of technological developments have led to the recent proliferation of UAV systems being used in different industries and hobbies.

Batteries

The development of the LiPo (Lithium Polymer) battery brought a number of improvements over the previous NiMH (Nickel-metal hydride) battery technology used in Radio Control (RC) Vehicles. They:

  • Have a larger capacity and last longer.
  • Are more powerful.
  • Are smaller and lighter.
  • Are cheaper.

This means that a UAV system can fly for longer, further and faster with a battery that weighs less.

Brushless Motors

The brushless motor has taken over from the brushed motor in the RC (Radio Control) industry with their:

  • Superior power.
  • Higher efficiency.
  • Greater reliability.
  • Higher accuracy.
  • Reduced noise.
  • Lower susceptibility to mechanical wear.
  • Longer lifetime.
  • Smaller size.

A brushed motor works by controlling the polarity of an electromagnet (coil of wires) between two magnets of different poles. The brushes in the brushed motor carry the electric current to the armature (electromagnet) of the motor by being in constant contact with it as it rotates. This causes wear to the brushes and at higher speeds friction, reducing torque and creating heat.

The brushed motor works in the opposite way, by having the coils of wire on the outside, with the magnet in the middle. It removes the need of the brushes but complicates the process as the position of the rotor needs to be sensed and the coils controlled in phase by an electronic speed controller (ESC). Although they are mechanically more complicated and cost more than brushed motors, their other benefits outweigh those of the brushed motor.

Brushed and brushless motors (http://www.eskyhelicopters.com/)

Brushed and brushless motors (http://www.eskyhelicopters.com/)

Brushless Gimbal

Linked intrinsically with the Brushless Motor is the Brushless Gimbal, this is a system which both; holds a camera steadily and level in a single position while the UAV moves around it thereby removing camera shake, and it also can be panned up and down and side to side in more expensive systems.

Camera gimbal pitch, yaw and roll. (http://science.howstuffworks.com/)

Camera gimbal pitch, yaw and roll. (http://science.howstuffworks.com/)

UAV brushless camera gimbals come in two types:

  1. 2-axis. This has two brushless motors which control the camera pitch and roll. This system relies upon filming in the direction that the UAV is pointing and is generally available on the cheaper UAV systems. These have legs which would be in the way if the camera was able to yaw.

    DJI Zenmuse H3-2D Gimbal

    DJI Zenmuse H3-2D Gimbal

  2. 3-axis. This has three brushless motors which control the camera pitch, yaw and roll. This allows cinematography to be conducted from UAV platform with the movement of the camera almost completely removed from the movement of the UAV. And in many cases a separate person can control the camera. These more expensive systems generally have retractable legs allowing the camera to pan left and right.

    DJI Zenmuse Z15-5D III (HD) Gimbal

    DJI Zenmuse Z15-5D III (HD) Gimbal

Gimbals can also be constructed using technology and how-to guides readily available on the internet. A number of Brushless Gimbal Controler Boards are available (including the V3 Martinez Board) as well as gimbal kits and brushless motors.

V3 Martinez Brushless Gimbal Controller Board

V3 Martinez Brushless Gimbal Controller Board

GPS (Global Positioning System)

GPS has a number of applications within the UAV industry:

  1. It is used to make flight easier by using the GPS signal to hold the UAV in one place by calculating if it is moving.
  2. It can be used together with an autopilot to automatically control the flight path of the system.
  3. The GPS co-ordinates at which each photograph is taken can be used within photogrammetry software to help with the locating and aligning of the photographs.
3DR uBlox GPS with Compass

3DR uBlox GPS with Compass

Mast

Mast

The GoPro

The lightweight GoPro series of camera was another enabling factor in the development of the UAV market. Many UAVs are in fact developed with the GoPro camera in mind. Not only are the GoPro series of cameras a lightweight powerful system but they also have wireless communication allowing the camera to be controlled, and the display to be viewed remotely.

Although there are now a number of different sports cameras the majority of low cost UAV systems, particularly those on the Kickstarter and Indiegogo crowdfunding platforms are designed with carrying the GoPro in mind.

Autopilot Systems

Autopilot systems can be very beneficial in the recording of different aspects of Archaeology and Cultural Heritage.

  • They can be used to plan a flight path for the UAV to take over the subject matter.
  • They can be used to create a grid pattern flight path as part of a mapping operation.
Mission Planner

Setting a flight path within Autopilot software

3DRobotics

3DRobtics is a personal drone manufacturing company which also manufactures open source autopilot systems that are the most popular in the world. They are used on many of the Kickstarter systems available.

The company produce two Autopilot systems:

  • The APM 2.6 System is based on the Arduino micro controller. It includes a 3-axis gyro, 6 DoF (Degree of Freedom) accelerometer, high-performance barometric pressure sensor and automatic datalogging.

    APM 2.6 Autopilot

    APM 2.6 Autopilot

  • The Pixhawk is an advanced autopilot system designed by the PX4 open-hardware project and manufactured by 3D Robotics, it includes a 3-axis 16-bit gyroscope, 3-axis 14-bit accelerometer/magnetometer, 3-axis accelerometer/gyroscope and a barometer. A digital airspeed sensor and GPS and compass can be purchased with the system and plugged into the Pixhawk board.

    Pixhawk Autopilot

    Pixhawk Autopilot

NAVIO

The NAVIO is an Indigogo project to build a Raspberry Pi based autopilot which attaches to the top of the credit-card sized computer allowing the construction and control of a UAV system with the powerful small computer system.

NAVIO Autopilot

NAVIO Autopilot

Follow Me Technology

A recently developed technology which is becoming increasingly popular in the drone industry is the ‘Follow Me’ technology where the drone will follow some sort of controller, whether a mobile phone / tablet / laptop or a specially designed piece of technology such as the AirLeash which comes with the AirDog drone. These systems use autopilots systems combined with GPS technology in the controller to control the direction and speed of the UAV system.

The ‘Follow Me’ technology is designed for the extreme sports industry where the drone can follow the user, filming as it flies, whether they are on a motorbike/mountain bike, surf board or other sports equipment. As well as controlling the flight path of the drone following the user it also controls the gimbal that holds the camera keeping the user in shot at all times. In some systems a number of pre-determined video filming techniques are made available with the control app which add to the abilities of the system.

Within Archaeology and Cultural Heritage the system has the potential for filming site tours, where the person giving the tour is tracked by the ‘Follow Me’ system, they would also have a digital audio recording system attached to them to record the dialogue which could be matched with the video in post-production. It would allow one person to do all of the production of the video.

Object tracking and following

Object tracking and following is an expansion of the ‘Follow Me’ technology where rather than following a GPS enabled device an object is selected within an interface and the system visually tracks the object. The UAV follows the tracked object with the camera being locked onto it.

Shift

The Shift has been developed by Perceptiv Labs, it attaches to existing UAV systems, such as those designed by DJI and 3DRobotics, as well as custom systems created with a number of different flight control systems and autopilot systems.

shift

Shift Object Tracking System

Shift Object Tracking System

Through the use of a Shift Eye video camera (attached to the camera of the UAV system) and a Shift Processor computer which plugs into the autopilot it provides standard UAV systems with the ability to track up to four subjects and follow and record them in flight. The subjects are selected using an app available on Android devices.

shift3

shift4

This could add to the site tours potential of the ‘Follow Me’ technology by selection the tour guide within the app when they are walking around, then also selecting the area under study when appropriate. This would be done best by having a second person controlling the app by watching the video, selecting the areas of interest when required and moving back to the tour guide when needed.

Autonomous

Development in autonomous flight of UAVs has a number of benefits for recording where a UAV could record the progress of an excavation at intervals, or record a standing building without any need for control by the pilot.

A number of simple autonomous technologies have already been integrated within commercial UAV technology.

Ultrasonic distance sensors

Ultrasonic distance sensors calculate distance by sending an ultrasonic wave and calculating the time it takes to receive the wave back.

MB1240 XL-MaxSonar®-EZ4™ High Performance Ultrasonic Range Finder

MB1240 XL-MaxSonar®-EZ4™ High Performance Ultrasonic Range Finder

They can be used in obstacle avoidance systems for UAVs, with the ultrasonic beam bouncing off objects in the UAVs path. The ultrasonic sensor is attached to the autopilot which can alter the path of the UAV when an obstacle is detected. With the APM autopilot the sensor it is enabled and calibrated within the Mission Planner Software.

Sonar_Setup

Optical Flow Technology

Optical flow technology is a technique where multiple images from a sensor are compared to determine movement, recent developments in technology mean that this can now be done in real time. It can be used in combination with Autopilot systems to stabilise the flight position of a UAV by detecting movement between photograph and altering the flight accordingly.

The PlexiDrone Indiegogo crowfunding project even comes with the technology demonstrating the growing availability and cheapness of the technology.

The PlexiDrone Indiegogo crowfunding project even comes with the technology demonstrating the growing availability and cheapness of the technology.

The Parrot Bebop Drone comes with Optical Flow Technology integrated into its design (8), with an image of the ground being taken every 16 milliseconds and then compared with the previous one.

Plexidrone

Plexidrone

The PlexiDrone Indiegogo crowfunding project also comes with the technology demonstrating the growing availability and cheapness of the technology in crowdfunding projects.

As well as being integrated into in some UAV technology the sensors themselves can be purchased separately; in UAV technology they come in two distinct types:

    • Mouse Based. The mouse based sensor is based upon the technology of optical computer mice.
3DRobotics Optical Flow Sensor Board with ADNS3080 mouse sensor

3DRobotics Optical Flow Sensor Board with ADNS3080 mouse sensor

  • CMOS Based. The CMOS based sensor uses a CMOS camera chip to capture the images.
    PX4FLOW KIT with MT9V034 machine vision CMOS sensor with global shutter

    3DRobotics PX4FLOW KIT with MT9V034 machine vision CMOS sensor with global shutter

    Vision Positioning System

    The Vision Positioning System present in the DJI Inspire 1 uses a combination of Ultrasonic sensors and Optical Flow Technology to control the position of the UAV in environments where GPS signals cannot reach. It can hold its position and stop when the RC controls are released.

    DJI Inspire 1 Vision Positioning System – [1] Two sonar sensors [2] One binocular camera.

    DJI Inspire 1 Vision Positioning System – [1] Two sonar sensors [2] One binocular camera.

    Intel RealSense

    The Intel RealSense is a new depth-capturing camera technology designed to be incorporated into the latest laptop and tablet technology. It has the ability, thanks to its specialised lens array, to alter the focus of photographs after they have been taken, like the Lytro Illum. It can also track hand gestures to control the computer systems and 3D scan real world objects.

    The new Astech Trinity Autopilot system incorporates 6 Intel RealSense cameras enabling 360˚ motion capture and obstacle avoidance . 
    The Astech Trinity Autopilot will be incorporated into the AscTec Firefly later this year.

    Asctec  Trinity

    Asctec Trinity Autopilot – http://www.theverge.com/

    Swarm Technology

    A lot of technical development has gone into the idea of drone swarms where multiples drones fly together in cooperation. Amongst the applications considered for their use are search and rescue, crop pollination, surveillance, monitoring traffic and as a distributed computing and communications network in disaster areas. Work at the GRASP (General Robotics, Automation, Sensing & Perception) Lab at the University of Pennsylvania has included navigating obstacles, Simultaneous Localization and Mapping (SLAM) using a Microsoft Kinnect and Laser Rangefinder, flying formation by monitoring each other’s position and co-operation in building structures.

    Within Archaeological and Cultural Heritage recording this has the potential for a swarm of UAVs to record areas in co-operation reducing the time taken, as well as the potential of using different technologies to record at the same time.

    Recording Technologies

    Introduction

    A UAV can act as a platform for a number of different recording technologies that can be employed in the recording of Archaeology and Cultural Heritage.

    Photogrammetry

    Photogrammetry is a technique for taking measurements from photographs and can be used to create a number of different results.

    The type of camera system used depends on the type of UAV system employed, the more powerful the system the heavier and more powerful the camera that it can carry.

    Weight is an important consideration; cheaper UAV systems are designed to only carry the GoPro or another extreme sports camera. While the more expensive/powerful systems can carry higher powered digital SLR cameras which record in much higher levels of detail and without lens distortion. The better quality the camera the more details are recorded.

    A number of 360° camera systems have been released which can be attached to the bottom of UAV systems. These have the potential to record many more photos than a single camera, this could potentially speed up photogramemtric recording as well as providing immersive experiences using VR (Virtual Reality) technology such as the Oculus Rift.

    360Heros 360° GoPro mount

    360Heros 360° GoPro mount

    Archaeological Mapping

    UAVs are used for mapping within a number of industries, and have already begun to be used in the mapping of archaeological sites. They provide an ideal platform for the creation of DTM (Digital Terrain Model) and DSM (Digital Surface Model) models which can be used in GIS (Geographical Information Systems) applications.

    This is the ideal project for a fixed wing UAV which can be deployed to fly over the area under study with a downward facing camera. The major benefits of such a systems is the stability, the amount of time that they can fly and hence the amount of recording that they can do in one flight.

    Using autopilot systems and software for programming the autopilot, such as Mission Planner, the flight plan for the UAV can be programmed.

    MP-FP-Screen

    Setting out a UAV light pattern in the Mission Planner Software

    Such software has the ability to create a grid flight pattern using the study area selected in the map interface, the altitude flown, the image overlap and the characteristics of the camera being used. Any alteration in the altitude, image overlap or camera specification (such as lens used) will alter the grid pattern to accommodate the alterations.

    Grid

    Setting out a grid UAV flight pattern in the Mission Planner software

    A grid of circular paper targets can be set up on the ground with each target being surveyed in using a GPS (Global Positioning System) which both increased the accuracy of the photogrammetry model and georeferences the results so they can incorporated with other data within a GIS system

    Standing Building Recording

    Photogrammetry has a long history in standing building recording which has be enhanced by the ability of the Total Station to survey points accurately. Limitations of ground based photogrammetry include the ability to record information high above the ground or masked from view. Traditionally this has been solved by using scaffolding, but his is an expensive and time consuming system which can also be dangerous.

    Another option is to use standard building photogrammetric recording techniques to record structures in high detail using a UAV to fly the camera at set heights parallel to the structure. This would mean that high quality imagery could be created using standard methods. The UAV can act as a mobile camera platform/tripod which has the ability to take to camera to heights not easily accessible by other means. Certain points on the building surface would need surveying in using a total station to georeference the 3D model created by the photogrammetry process and to make it more accurate. Orthophotos (geometrically corrected images) can be created from the images taken which are an important element in building recording.

    Increasing development in autonomous flight can be used to automate the flight patterns having the UAV automatically record buildings.

    HDR (High Dynamic Range)

    High Dynamic Range photography is a technique where multiple images are taken with different exposures (bracketing), these are then merged together using computer software to form an image with all of the detail from the images. Many modern digital camera have an auto-exposure bracketing (AEB) setting which allows this to set up on the camera to be done automatically. There are also dedicated HDR cameras. It provides images which are close to what the human eye can see and with more information than standard photographs.

    The problem with using UAVs for this technology is that the images need to be taken while the camera is perfectly still, and even with a camera gimbal a UAV is likely to move slightly between the photographs being taken.

    HDR photographs can also be used in photogrammetry.

    Video

    The video capabilities of most cameras that UAVs carry mean that they can record videos. As we have already seen the ‘Follow-Me’ technology has the potential within archaeology or cultural heritage to record a site tour, filming the tour guide as they walk around site, with a separate digital recording system recording the audio which can later be combined with the video footage in post-production. The Hexo+ UAV Director’s Toolkit allows different filming scenarios such as crane; pan, tilt, crab, dolly, 360° around you, and far-to-close/close-to-far.

    The UAV has the potential to create immersive fly through videos of sites thanks to the recent introduction of multi-camera systems or systems with multi-lens cameras, this can aid in public interaction and interest.

    Archaeological Prospection

    Lidar (Light Detection And Ranging)

    LIDAR is a technology which has already proved useful in Archaeology and Cultural Heritage, it works by firing a pulsed laser beam at the ground and recording the returned beams, the time it takes for the beam to return is recorded and this is used to determine the distance. It is tied to the flight instruments of the light aircraft carrying the LIDAR and accurately records the 3D position and height of the results creating a dense point-cloud of the topography being recorded. The resulting LIDAR point data can be loaded in GIS systems.

    It has the potential to discover archaeological remain under woodland by removing points from the LIDAR point-cloud leaving only the points that hit the ground between the forest cover.

    Although not a cheap technology a number of LIDAR systems have recently been developed which can be carried as a payload on UAV systems. This includes the Phoenix Aerial Systems AL3 S1000 Copter which combines a DJI S1000 Octocopter with their AL3 technology which includes the Velodyne HDL-32 high definition LiDAR sensor.

    AL3 S1000 Copter

    Phoenix Aerial Systme – AL3 S1000 Copter

    If the UAV system recorded high quality photographs as well, these could be recorded in a separate flight using the same flight path, these could be used to overlay the LIDAR data.

    LIDAR can be analysed with a number of computer tools enabling more information to be visualised.

    LiDAR Data with Multiple Hillshades and with Principal Component Analysis (PCA).

    LiDAR Data with Multiple Hillshades and with Principal Component Analysis (PCA).

    Multi-Spectral and Hyper-Spectral Imaging

    Multi-Spectral and Hyper-Spectral imaging involves the recording of the electromagnetic spectrum outside the visible spectrum, this includes the infrared which can detect differences in ground moisture helping to determine what is below the ground level.

    Traditionally this has been done using satellites but spectral imagers are also available for UAV platforms.

    Comparative multispectral imagery of prehistoric field systems near Stonehenge © Historic England.NMR; Source Environment Agency

    Comparative multispectral imagery of prehistoric field systems near Stonehenge © Historic England.NMR; Source Environment Agency

    Ground Penetrating Radar (GPR)

    Ground Penetrating Radar is a technology that is used within field archaeology to discover buried features, it works by recording reflected radio waves that have been transmitted into the ground. GPR can be used on areas such as concrete, stone and tarmac where other geophysical techniques won’t work.

    MSc students from the University of Southampton carrying out a GPR survey in the vicinity of the Episcopio, between Portus and the Isola Sacra, Italy (https://kdstrutt.wordpress.com)

    The potential of having UAVs carry Ground Penetrating Radar recording equipment has already been tested in a number of fields including the detection of IEDs (Improvised Explosive Devices) and mines and the characterization of soil properties. But studies, including one at the University of Leicester, are looking into the potential of GPR carrying UAVs in archaeological recording.

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    Gray, S. UAV Survey: A Guide to Good Practice, 2014. Part 1: http://www.jiscdigitalmedia.ac.uk/infokit/3d/uav-survey Part 2: http://guides.archaeologydataservice.ac.uk/g2gp/AerialPht_UAV

    Jacobs, Axel. “High dynamic range imaging and its application in building research.” Advances in building energy research 1, no. 1 (2007): 177-202.

    Li, Zhe, Yan Li, and Nankai Tian Jin. “Photogrammetric recording of ancient buildings by using unmanned helicopters-cases in China.” International Archives of the Photogrammetry, Remote (2011).

    Michael, Nathan, Shaojie Shen, Kartik Mohta, Yash Mulgaonkar, Vijay Kumar, Keiji Nagatani, Yoshito Okada et al. “Collaborative mapping of an earthquake‐damaged building via ground and aerial robots.” Journal of Field Robotics 29, no. 5 (2012): 832-841.

    Ntregkaa, A., A. Georgopoulosa, and M. Santana Quinterob. “Photogrammetric Exploitation of HDR Images for Cultural Heritage Documentation.” ISPRS Annals of the Photogrammetry, Remote Sensing and Spatial Information Sciences 5 (2013): W1.

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