Albert Sarvis, PMP, GISP – ACG Partner & Lead Pilot/Imagery Analyst
Nearly every day we read about new uses for small unmanned aerial systems (sUAS or Drones), especially for image collection and processing. The equipment and technology are also constantly evolving. Aerial Content Group looks to keep up with these advances and that necessitates ongoing testing. As drones continue to evolve so do their cameras and the apps that help users control them. Making the jump from a DJI Phantom 3 drone released in the 2015 with a 12MP camera to the 20.8MP camera of the DJI Inspire 2 is a significant change. In addition, the configuration and operation of the more advanced Inspire 2 requires an improved inflight app, called DJI GO 4, and a full range of obstacle avoidance sensors.
Last weekend we flew a new commercial property site outside of York PA to test this new drone and capture much higher resolution images. While we have experimented with several mission planning apps the Pix4D Capture app (Image 1) has been the most reliable and pairs nicely with the industry leading image processing software Pix4D (Image 2). The biggest difference with our newest drone, and the difference most important to our clients, is the image resolution. The flight that produced the images below was conducted at 200 feet. The same flight with a Phantom 3 drone would produce images where one individual image pixel would equate to 1.05 inches on the ground. Our Inspire 2 Zenmuse X5s camera produces a 0.55 inch/pixel resolution at the same height.
This image shows the Pix4D Capture mission planning interface used for our testing. Important information such as flight time, mission area, and altitude are configured and reported here. This app will also allow for more complex polygon shaped missions. We work with our clients to find the best mission extent and altitude for their needs.
Image 1: Pix4D Mission Planning Interface
For this project 416 individual images were captured. The screen shot below depicts the location of each photo and the green “rays” depict which images captured the same area on the ground. Because multiple images from multiple angles captured that location a 3D model can be produced.
Image 2: Pix4D Ray Cloud
With the image processing software, we can produce both 3D models (Image 3) and large area aerial photos (Image 4). Image 3 and link below depict this 3D modeling capability. This link is to an interactive view of the resulting 3D model but can also be delivered in .obj file format for use in other 3D modeling software packages. For construction sites a Digital Surface Model (DSM) can also be delivered. This particular 3D site view may be used to help perspective investors visualize the site without having to leave the office, and to insert mock-ups of the proposed buildings.
Image 3: 3D Model hosted online
The aerial photo below, comprised of all 416 individual stitched photos, depicts another potential client deliverable. The ability to visually detect information down to just half of an inch is a unique and valuable benefit of drone photography.
Image 4: Orthophoto
This final view (Image 5 & 6) shows the detailed resolution possible. Without resizing the composite image produced for this site was a nearly 1.2GB TIFF file. This also is an essential element of ongoing training and testing. As resolution increases so does the processing effort of our computer hardware. Every element of our flight operations and post processing procedures must be constantly evaluated and adjusted.
Image 5: Detailed view
Image 6: Detailed view 2
It is important to note that the testing described in this post did not include the use of ground control points. For measurement and positional accuracy, surveyed ground control is crucial. This topic, and Aerial Content Group’s use of Licensed Surveyors, will be included in our next blog post.