GCP Order of Assignment/Usefulness Questions

On a project I’ve been playing with, I have good overlap and I have a plethera of “natural”(?), control points.

I’m aware of the need of a minimum of 3 photos for each control point …
I’m aware(I think), that if a photo is assigned a GCP, no other GCP can be assigned to that photo
But …
Are too many GCP on a run better or worse than too few
Should 3 adjacent photos for a GCP take precedent over 3 non-adjacent photos(north-south-north)
Should 6 adjacent photos with a reversal after 3, be used or only 3 one direction or the other(north-south)
Should GCP on boxes, septics, gas tanks, roof tops, be assigned their actual elev, ground elev or 0
… what about structures in trees(ground not visible)
Should power poles be used for control, or a point a foot away from the pole be used(no marker)
… same with building corners
Can elev be assigned to points in a creek with Lon, Lat, elev, if the point is somewhat nondescript

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You can assign multiple GCPs to a photo and multiple photos to a GCP. Many-to-many so assign away!


You can, but it generally doesn’t make much sense as the geographic distribution of the two GCPs would be too small to be helpful.

They can eventually lead to over-fitting or other issues with compounding error. It is best to try and keep the highest-quality tags you can for each GCP.

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