139th Street in Vancouver, WA is serving as a testing ground for comparing ground models I create with modern photogrammetry and structure from motion (SfM) with traditional models created using survey points and breaklines. I have been working on this new methodology with my partners S&F Land Services. 139th Street is a roadway project S&F surveyed for the City of Vancouver. I am working with an old colleague of mine, Josh Brockway (now an employee of S&F Land Services) to compare both horizontal accuracy as well as vertical accuracy between the two data sets. Throughout this process I have learned a great deal about best acquisition techniques for roadways as well as best processing methodologies in breakline creation.
Currently I’m working on a “Version 3” of this roadway which we re-surveyed September 22nd. This time I flew differently and a little bit higher achieving a slightly bigger GSD of 0.7cm but because of the time of day and the camera angle parameters I was able to get more coverage under low branches and the surface of the roadway came out far less noisy. We also acquired 3 more Air Targets in a better pattern for processing giving me an RMS error in Z of 0.02ft which is pretty great.
The images above are a comparison of the raster elevation values between the UAV Ground Model and the survey one. Yellows and greens are a better fit. As you can see the top one is fairly off but the bottom one is aligning better. It often takes a lot of practice to figure out the right acquistition techniques and correct processing settings to create high quality data. With TLT Photography I aim to establish my methods before I agree to a contract that requires results I’m not sure how to produce yet. Working with Chris and Josh at S&F Land Services has been fantastic as they also agree it is important to have proven concepts before saying “yes we can do that” to potential clients.