In my position I talk to a lot of different clients about their requirements for drones. I hear of clients wanting high resolution aerial photography, elevation models, performing volumetric analysis, outputting point clouds for updating engineering designs, change monitoring and inspection scenarios. Every client has different thoughts and ideas on how they best make use of their investment. In all of these great ideas I often find that there is a great void between the understanding of what a client is looking for and their understanding of what is achievable.
Whether you purchase a helicopter, smaller quad copter or a fixed wing drone, all are delivered a flight control unit and flight management software. You’ll often though have to supply your own Smart Phone or tablet to run the software. However, it is not until you decide on exactly what you want to use the drone for, does the realisation of what is really required to achieved those results become apparent. If you are going to use it for talking single aerial pictures or video then the manual flight controller might be sufficient, however if you want to be able to use the drone for comprehensive orthomosaics or elevation modeling then there are key considerations that are required.
1) Mission Planning
Mission planning is critical for achieving the optimal flight paths to capture enough imagery to cover your area of Interest. With mission planning you define the area of interest you need to be covered by the drone. You supply the height you wish to fly at and then the software works out the optimal flight path. In many cases it is simply a case of selecting go and the mission planning software controls the take off, flight path, image capture and landing. In some cases the software is even smart enough to know when the drone is getting low on power, return it home mid mission, allow you to replace the battery and then automatically complete the mission. The key is that each image is automatically captured with all the georegistration information about elevation and location.
Interestingly, I find this perhaps the least understood part of the whole aerial image capture process. Generally, drones don’t come with the mission planning software. Mission planning software is often free and one piece of software can interact with many different types of drones. The software has to be deployed separately to the control tablet or device which interfaces with the drone. Commonly used packages include
- Pix4D Capture
- Drone Deploy
- Maps Made Easy
- 3DR SiteScan
- Ebee Emotion
- DJI Ground Station Pro
Which is best? Well I always recommend to clients try them all. Generally each will interface with the most common drones out there (DJI/3DR/Ebee/Trimble). Each will navigate your drone for you and each will georegister your photo’s. The most important thing is that you practice flying with your chosen software and gain confidence in understanding how it works. Each is different and each has different level of control
NOTE: The DJI Phantom Pro+ comes with an attached tablet with an excellent Android screen for outdoor work but it does not allow you to load any of the Mission Planning software. So understand your needs for your drone before purchasing.
2) Image Overlap
Image overlap is important for post processing the imagery into a seamless mosaics and elevation surfaces. For optimal results it is recommended that the overlap between images in the forward direction is 80% and 70% in the sideways direction. In some of the Mission planning software such as Pix4d this can be adjusted where other software which understands the camera, drone speed and height it automatically sets the overlap for you.
3) Field of view
Field of view is an interesting aspect of aerial photography. The type of lens used and the subject being imaged needs to be considered. For example, the GoPro camera has a very wide field of view producing a distorted fisheye image. Whereas mapping lenses have a narrow field of view, are high resolution and have very good geometry control. The choice of lens is dictated by your requirements.
4) Ground Control.
Now Ground Control I find is something that a lot of people fail to realise the importance of. Often people fly the drone for the purpose of mapping failing to realise that the GPS used in the Drone is +- 5m in both X & Y but also in Z the direction. What does this mean? Well it could mean that if just aerial photography is being captured then there might be some horizontal distortion. Often this distortion can be accommodated in the post processing software such as Drone2Map. If though the out puts are DEMS’s, point clouds or 3D models then ground control is very important. +- 5m in the Z direction can lift the models off the ground or push it through the surfaces. If If Volumetric calculations are being produced and then being compared with earlier dates, there is little confidence in the change between dates as the DEM’s are not tied to the earths surface. If the point cloud is to be used in engineering work then it has to be tied back to the earths surface.
So how many ground control points is sufficient, general between 3-5 evenly spaced through out the Area of Interest and a couple of non-active ground control for accuracy checking later. Importantly the Ground Control used must be visible in the imagery and the coordinates must be known in XYZ direction.
Collector for ArcGIS can be used to capture this ground control as described in the following Esri blog: https://shar.es/1TjLzP Also, a good example of automated ground control is a product call AeroPoints: http://bit.ly/2tV4GKt
If ground control is difficult to layout, then it is worth considering deploying a Drone with RTK GPS. A RTK drone applies realtime GPS correction for each image from a basestation and removes the need for the ground control.
So simply purchasing a drone and going flying to capture suitable GIS datasets requires a lot more thought and planning. Often I see an expensive pieces of equipment on the shelf because the ground work was not done first.
Finally, and perhaps the most important consideration is will the drone be flown licensed or unlicensed. Checkout the CASA Part 101 amendment for full information and considerations http://bit.ly/1sNxnt4