Excess Green Index

I am using a standard Phantom 4 proV2 to take pictures of potato crops here in Tasmania.

I am using WebODM running on Ubuntu18.04 updated to latest version to create my orthophotos. It works faultlessly and I really like the new plant health options such as VARI.

Another index I am using to extract more of the variation in the green potato canopy is the Excess Green Index.

I use the Raster Calculator in QGIS to produce this index (2*Green)-(Red+Blue). I display the image as pseudo color ranging from red through yellow to green.

Is it possible to add this index to list ?

To give an example of how I am displaying the Excess Green index have a look at this image.
Carr Ranson 79DAP ExGr 15cm

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That would be a great addition. Would you be interested in opening a pull request by editing https://github.com/OpenDroneMap/WebODM/blob/master/app/api/formulas.py ?

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Thanks for the opportunity. I had a look at the link but I have done no programming so don’t understand what you mean by a pull request.

Using your VARI formula
‘VARI’: {
‘expr’: ‘(G - R) / (G + R - B)’,
‘help’: ‘Visual Atmospheric Resistance Index shows the areas of vegetation.’,
‘range’: (-1, 1)

This what ExGr should look like

‘ExcessGreen’: {
‘expr’: '(2*G)-(R+B),
‘help’: ‘Excess Green Index emphasizes the greenness of leafy crops such as potatoes.’,
‘range’: (-50,150)


No worries, it’s pretty simple, no programming skills required:

  1. Register an account on GitHub.
  2. Edit the file via this link: https://github.com/OpenDroneMap/WebODM/edit/master/app/api/formulas.py
  3. Press the green button at the bottom of the page, adding a description of what was changed.

OK I’ll give it a go.

Is there a way I can test it on my copy of WebODM ?

You can if you setup a development environment. https://docs.webodm.org/#for-developers

Done as you suggested.

Like you said it was self explanatory and not very hard.


Just updated my copy of WebODM and checked out the added EXG index.

It worked like a charm and gave the same view as I expected.

The next thing I thought of was the ability to trim the orthophoto to the field boundary.

Any ideas ?

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There is a cutline option in processing options for exactly this.