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I have a NVDI WMS layer configured to show NDVI index, and I need to let the user choose the color ramp.

Is there a way to send parameters from the client and get then inside the evaluatePixel function?


According to reference this is the signature of the method, but I can’t find an example that uses inputMetadata or customData or a reference about their content.


function evaluatePixel(samples, scene, inputMetadata, customData, outputMetadata) {

}

Thank you

You can simply construct the whole EVALSCRIPT on the client and pass it to the WMS as a parameter, in these steps:


  1. Construct an EVALSCRIPT, e.g.
    return [B04];


  2. Base64 encode this script
    cmV0dXJuIFtCMDRdOw==

  3. Add it to the WMS request:
    https://services.sentinel-hub.com/wms/<INSTANCE_ID>?LAYER=NDVI&EVALSCRIPT=cmV0dXJuIFtCMDRdOw==&...

In this way you will override the original script of the NDVI layer.


You might also be interested in our JavaScript helper library:

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18bf53bcd7b157a41683561fbb4374af1ae3c339.png


GitHub - sentinel-hub/sentinelhub-js: Download and process satellite imagery...



Download and process satellite imagery in JavaScript or TypeScript using Sentinel Hub services. - GitHub - sentinel-hub/sentinelhub-js: Download and process satellite imagery in JavaScript or TypeS...










The easiest way for user-defined color ramp is to generate the evalscript on the client side and pass it as a parameter.

There are also utility functions for evalscript that might come handy for defining the color ramp / color gradient in the evalscript (documentation here).

Use of inputMetadata, customData and outputMetadata is not necessary for this use-case, they are useful for more complex evalscript.

Cheers.

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