Shadows and GCP Placement. How will they affect the processing?

Will "Shadows" have any affect on the aerial processing?

A small site with buildings that cast shadows on part of the area was selected for testing to see just how they might affect the outcome. The GCP polygon area was also tested to see the affect it has as well. The Green box is the GCP Polygon area. Points D & E are outside of the polygon area. Points G, H, I & J are located above the ground to check how accurate the vertical components are compared to direct levels. Points I & J are on the roof peak so no direct levels were run to these two points. The site has a vertical relief of about 17 feet from point 2 to point 4. Below are the results.

Four drones were used for this test. The Mavic Mini, Mavic Air 2, Mavic 2 Pro and the Inspire 2 with 5xs (15mm lens). The AGL's were at 100, 200 and 300 feet. Front and Side overlap was at 70%.

100 AGL Result

200 AGL Result

300 AGL Result

The charts show the vertical accuracies from the aerial triangulation compared to direct levels for the GCPs and check points. The "Sweet Spot" is the accuracy of the aerial triangulation that will meet the ASPRS Class 1-cm and Class 2.5-cm.

Conclusion The shadows did not seem to have much of an effect except for the 300 AGL flight and then it was only minimal. The check shots outside of the GCP Polygon did have a huge effect for the vertical component. This indicates that the GCPs must be positioned on a site that will strengthen the aerial triangulation to give the best results. Randomly placing the GCPs can produce errors for extrapolation outside of the polygon boundary. The distance between the GCPs needs to be balance to provide strength to the solution. Below is my GCP recommendation for drones with non-metric cameras in order to meet the ASRPS Class 1-cm & 2.5-cm accuracies.

You will need to do some testing of your drone platform to determine the optimal GCPs that need to be set and their location. Each drone platform maybe slightly different.

www.cc4w.net "I fly Drones for a living mapping the earth one (1) acre at a time and write DIY surveying math/mapping books/videos for fun!"

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