Mission planning for heavily forested 80 acres on slope

The Hangar
#1

Hey folks,

Asking for advice on mission planning.

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?

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#2

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:

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:

image

image

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#3

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).

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#4

Ok, great thanks for the input.

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)?

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#5

There’s no real penalty to always flying 5 degrees off nadir, and lots of benefits, though complex terrain is less subject to systematic lens errors.

Two grids, the second rotated 20 degrees from the first.

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