Do large differences in GSD screw up processing?

[jazzyj]

I've read that for a large site where the topography has large changes in elevation, if you fly the same altitude AGL from the starting point, it can create issues in processing.

However, if you have a target GSD, and therefore a target altitude AGL, as long as you never exceed that altitude so that the variation in GSD will always be better GSD than the target, it would seem to me that shouldn't cause any issue.  The issue would be if the GSD was a lot worse than the target at certain points in the flight path.  Or is the potential issue in processing just any big difference in GSD despite whether it better or worse resolution?

Example:  I want to generate a topographic map (DEM/DSM) where I want the elevation measurements to be accurate within 12 inches.  It is widely stated the elevation measurement are *typically* accurate within 3 times the GSD.  So I need a GSD of 4inches/pixel.  (In reality it will be better because that GSD allows for an altitude above 400ft).  So if some of the photos have a GSD of 1inch/pixel because of high points on the site being surveyed, whereas others will be 4inch/pixel at the low points of the site, is that going to create a problem in processing?

[cadm8]

What platform are you using to get your photos?

[jazzyj]

DJI Phantom 4 Pro Drone. 

[n@sk]

GSD is convenient for "typical" rules of thumb for accuracy predictions with regard to relatively flat scenes photographed by a camera  with its image plane parallel to them.

I suppose what you have read means "do not count on it and use check points unless you are happy with over-designing your survey or have really low expectations".

Think about the limiting case of a cliff and what GSD and AGL mean around such areas.

The processing part, excluding the potential occlusions, is being taken care of by affine invariant feature descriptors and (global?) dense matching algorithms.
The larger the depth variations and projective distortions the harder we make it for them to do our lovely job.

[cadm8]

DJI Phantom 4 Pro Drone.

Use a planning software like mission planner to get your waypoints and then use Litchi to fly them using ground awareness. That way you will get a constant GSD throughout the mission