Adding calcution to band in image collections

openEO Platform
1

When I dowload my images from the server I am missing the ndwi band in results. The ndwi calculation cube_ndwi = (B03 - B08) / (B03 + B08) was done from cube bands and then it was added t cube its band. (cube.add(cube_ndwi)) howver I can not see the it ndwi in my final result. however I can see the ndvi which was calculated before. How ndwi can be added to final result?

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2

Hi @sulova.andrea ,
Maybe the problem is theprocess you are using ot merge the datacubes:
I guess that “add” should be used to perform a sum, while you need probably to use the “merge_cubes” operation. Can you try and see if this resolve your issue?

1 Like
3

@sulova.andrea as @paolo.filippucci said, you would need to use merge_cubes like this:

B03 = cube.band('B03')
B08 = cube.band('B08')

NDWI = (B03 - B08) / (B03 + B08)
NDWI = NDWI.add_dimension(name='bands',label='NDWI')

cube = cube.merge_cubes(NDWI)

The result will then contain B03, B08 and NDWI bands.

4

The most efficient approach is actually to use a built-in function from the client, it’s based on the ‘Awesome spectral indices’ project, which supports a large number of predefined indices. In this case, you simply need ‘append_index’
https://open-eo.github.io/openeo-python-client/cookbook/spectral_indices.html#openeo.extra.spectral_indices.append_index

So in your case, it becomes:

from openeo.extra.spectral_indices.spectral_indices import append_index
append_index(cube,"NDWI")

it avoids doing a ‘merge_cubes’, making it a bit faster.

5

Thank you! append_index works well

6

Hi,
how can i use append_index in R?

7

The “awesome spectral indices” and this append_index function are extra features specifically from the openEO Python client library. As far as I know there is no equivalent yet in other client libraries, like for R.

8

The Web Editor also supports the awesome spectral indices, but doesn’t have append_index. Nevertheless, append_index is just a convenience function and can be emulated both in R and the Web Editor.
What processes does append_index use in the background, @stefaan.lippens ?

9

append_index does something like this

{
  "process_id": "apply_dimension",
  "arguments": {
    "dimension": "bands",
    "process": { "process_graph": {
       ... array_element ...
       ... array_element ...
       ... subtract ... add ... divide ...
       "arraymodify1": {
            "process_id": "array_modify",
            "arguments": {
                "data": {"from_parameter": "data"},
                "index": 12,
                "values": [{"from_node": "divide1"},],
            },
            "result": True,
        },