Site is about 1.0km x 2.5km and I will be there for next 18 months. So plenty of time for tweaking and refining of processes (if only I can get something to work).
For grid flights I have used pix4d capture app (but it only allows rectangular areas and crashes a lot). Dronedeploy app works much better- allows variable shapes (can upload shapefiles for areas to map). Both allow you to enter flying altitude and overlaps and the software then generates flight path and flies in autopilot capturing images as required. Straight down images only however.
Combining of 120m and 100m flights didn’t work- I get this cuda error- 30- unknown error- so it’s not a memory issue by the sounds of it- a graphics card problem.