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

4 Likes
#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)?

1 Like
#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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#6

Ended up using DroneHarmony, after clipping a piece of the USGS DEM to utilize their terrain mission planning.

Screen Shot 2020-10-29 at 08.18.11

Hoping to collect this weekend and process the following week!

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#7

First attempt at an orthomosaic

Just ran:
docker run -ti --rm -v /Users/<myUserName>/datasets:/datasets opendronemap/odm --project-path /datasets project --dsm

Looks ok when zoomed out but there are some freaky seams and distortions in there :smiley: Exhausted, will have a deeper look into this tomorrow

Screen Shot 2020-11-01 at 20.32.37

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#8

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 :ok_hand:

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#9

By a couple weeks, I mean try it now. 2.1.0 is now in. Update everything and rerun.

Still set your texturing nadir weight high: somewhere between 28 and 32 should do the trick.

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#10

Not to revive a dead topic, but UGCS is a great tool for complex terrain mapping. Terrain awareness is excellent, and their support is top notch.

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#11

Thanks for the tip, looks cool!

1 Like
#12

Did a big write up about my end-to-end journey with OpenDroneMap. Have a look if you have the time

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#13

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