I am flying a large area in the mountains. I have GCP’s set up for a small specific building within that area. The flight covers over buildings with large elevation changes. About 800 images or so. Flying such a large area with elevation changes, is it necessary to even try to use GCP’s?
Do you need actual global positioning and/or relative accuracy better than 2ft? I would at least spray or put down some tie-points in key areas to help the software find strong matches across images. They don’t have to be survey-grade located just used by the photogrammetry software. What drone are you using?
I just already have them set up around one building. I am reading if I wanted to use GCP on the current flight, I would likely need to have a GCP at most major elevation changes.
Since you are focused on the structure using GCP’s only there around it should be fine. Your error report will look terrible but the desired area will be tight. It is very important on large sites with a lot of relief that you get as much of the site encompassed or if you are doing a project that requires much great detail on tops/toes of steep slopes you’ll want to mark the tops and toes of the gray brakes. You forgot to mention which drone you are using.