Excess Green Index

Developers Chat
1

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
Carr Ranson 79DAP ExGr 15cm2730×3512 2.93 MB

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2

That would be a great addition. Would you be interested in opening a pull request by editing WebODM/formulas.py at master · OpenDroneMap/WebODM · GitHub ?

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3

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)
},

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4

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

  1. Register an account on GitHub.
  2. Edit the file via this link: Sign in to GitHub · GitHub
  3. Press the green button at the bottom of the page, adding a description of what was changed.
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5

OK I’ll give it a go.

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

6

You can if you setup a development environment. WebODM Documentation

7

Done as you suggested.

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

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8

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 ?

1 Like
9

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

10

Hello edblanch, I am new to the topics and I would need your help for the vndvi script in the qgis raster calculator. That conversation is locked so I dropped a comment here! Would love to hear from you, chhers!

1 Like
11

Hi, Koroil

What crops are you looking at ?

The two indices I use looking at Potato crops here in Tasmania are:-
1 VARI (Green-Red)/(Green+Red-Blue)
2 Excess Green EXG (2*Green)-(Red+Blue)

These two indices are easy generate using QGIS Raster Calculator.

I’ve had a quick look at the visible NDVI but so far its not giving anymore information than VARI or EXG.

12

Hi, can you help me with the gradient creation for this excellent result that you showed