Generating Accurate Ground Contours

PIX4Dmapper PIX4Dmapper Questions/Troubleshooting
1

I am having problems generating accurate ground contours. the site is a rectangular shape with 12 GCPs (4x3 equally spaced) within the area (all points were shot with a survey grade GPS). I have gone through the process of the rayCloud editor but 4-5 of the GCPs have an elevation error of more than 0.5 feet. Along with having issues with several GCPs, in the rayCloud, there are hundreds of points 30-40 feet below and above the ground but only in the street paved with asphalt while the dirt interior of the site is as it should be. I have tried cleaning up the point cloud by putting out of place points in the deleted category as well as changing GCPs with elevation errors more than 0.5 feet to checkpoints. So what I am asking, is there anything I am doing wrong? I need survey grade ground contours and have tried everything I have ever seen in a webinar or how-to video. Any help anyone could offer would be greatly appreciated. Thank you.

Additional Info:

Phantom 3 Advanced was used to take pictures of site

64 pictures in total @ 150 ft

2

How big was your site? If it is a small area, you have way to many GCPs. Did a registered surveyor set your GCPs? Are the GCPs located areas with good photographic overlap? I would need a lot more information to answer your question

3

Steve,

Did you re-run Step 3 after moving the “bogus” points to the deleted layer ?

I ran into a similar situation before and started the project completely over from scratch only using my best GCP’s, and it worked fine.  

 

I’ve found adding manual tie points adds much more reconstruction information than GCP’s, as I was previously guilty of using too many GCP’s (1cm Survey Grade).  

It’s my understanding (could be wrong) that GCP’s are only used to translate the 3D model to your GCP coordinate system/location.  

The automatic and manual tie points contribute to the Model’s geometric Accuracy, not GCP’s.  

I’ve produced contours at 1" intervals that matched check points within 1/2 the interval, using only 5 GCP’s, but flying much lower of course.