how to add a new formula into spectral-indices-dict.json file

[gaowudao]

Hello, I have a formula,called "WD", ("formula": "19.4260 + 9.2603 (G / R) - 57.9165 (R.log()) + 86.9934 (G.log()) - 6.4577 R - 17.6220 * (B.log())"), and added it into spectral-indices-dict.json file.

What I did:

f1 = ee.Feature(ee.Geometry.Point([120.076432, 30.86733]).buffer(10),{'ID':'A'})

fc = ee.FeatureCollection([f1])

S2 = (ee.ImageCollection('COPERNICUS/S2_SR') .filterBounds(fc) .filterDate('2021-04-30','2021-08-30')

.filter(ee.Filter.lt('CLOUDY_PIXEL_PERCENTAGE', 40))

.maskClouds()

.scale() .index(['NDVI','GNDVI','EVI','WD']))

By Regions

ts = S2.getTimeSeriesByRegions(reducer = [ee.Reducer.mean()], collection = fc, bands = ['B2','B3','B4','B5','B6','B7','B8','B8A','WD','MSK_CLDPRB'], scale = 10)

df = geemap.ee_to_pandas(ts, selectors=['B2','B3','B4','B5','B6','B7','B8','B8A','WD','MSK_CLDPRB'])

error Exception: Image.parseExpression: Expression parse error at character 45: '19.4260 + 9.2603 (G / R) - 57.9165 (R.log()) + 86.9934 (G.log()) - 6.4577 R - 17.6220 * (B.log())' ^.

[davemlz]

Hi, @gaowudao!

In the expression of the formula you should use the method as a function itself. The correct form of the formula would be this:

'19.4260 + 9.2603 * (G / R) - 57.9165 * log(R) + 86.9934 * log(G) - 6.4577 * R - 17.6220 * log(B)'

Note that the log() function is not a method of the band :)

Let me know if it works!

Also, you must define the bands, short_name and type attributes to make it work correctly :)

PD: Another option (if you want) would be adding the index to the Awesome Spectral Indices and then computing it in eemont by setting online=True in the spectralIndices() method! :) Example below:

f1 = ee.Feature(ee.Geometry.Point([120.076432, 30.86733]).buffer(10),{'ID':'A'})

fc = ee.FeatureCollection([f1])

S2 = (ee.ImageCollection('COPERNICUS/S2_SR')
    .filterBounds(fc)
    .filterDate('2021-04-30','2021-08-30')
    .scaleAndOffset()
    .spectralIndices(['NDVI','GNDVI','EVI','WD'],online = True))

I'll close the issue with this comment, but please feel free to re-open it if required!