Wanting to sort out rough orthos and 3d model of about 80 acres of forested property.
Known mission planning factors:
elevation of the terrain changes over this area, so if flown at one altitude, overlap on imagery will be variable
Lots of tall trees, so it might be hard to compose a nice 3D output
Been reading around including https://github.com/OpenDroneMap/WebODM/issues/6 and else where (DroneDeploy, Hivemapper, DroneHarmony, DroneMapper, etc) and I think I am settling on using Litchi as a mission planner and figuring out ODM for the processing.
Has anyone used Litchi for mission planning? Do they have reliable mission plan generator for 3D missions over varied terrain?
I have heard good things about Litchi, though I haven’t tried it myself.
For forest, especially over varied terrain, you will need lots of overlap, but also a fair amount of variation in flight angle. In the docs, we document how to, in a very robust way, ensure perfect camera calibration: https://docs.opendronemap.org/tutorials.html#calibrating-the-camera
I need to rewrite this section, as there are easier ways to achieve good camera calibration. But this description of how to fly is very useful for forested landscapes, specifically performing a pair of cross-grids separated by 20°, ideally with a 5° forward facing camera.
Crossgrid overlap percentages can be lower than parallel flights. To get good 3D results, you will require 68% overlap and sidelap for an equivalent 83% overlap and sidelap.
As you have varied terrain, you may want each sub-flight (of the 8 subflights) to have 69 or 70% overlap / sidelap for overlap in excess of 83%
Doing so will give you really a really nice surface model and accurate orthophotos:
One thing I would add: if you use a flight planner that allows for terrain following, you can just fix your overlap and sidelap at 69 (83% equivalent).
I did see the 5% of nadir shift in camera suggestion to act as a camera calibration of sorts but you also suggest it for complex terrain? And should every mission have the 5% shift or is it every second mission? And I was planning on doing two grids over the same area but you are suggesting eight? Or was it that each mission had eight sub-flights (eight sequences it was flying)?
Two things: increase your --texturing-nadir-weight to ~32, but also if you wait a couple weeks, you’ll likely see much better results. The 210 branch is
Exhausted, will have a deeper look into this tomorrow
