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I would like to compute vegetation indices like GCVI or EVI and wanted to see how I can adapt the script below (taken from Sentinel Hub Batch Statistical — Sentinel Hub 3.9.1 documentation):


ndvi_evalscript = """

//VERSION=3



function setup() {

  return {

    input: :

      {

        bands: :

          "B04",

          "B08",

          "dataMask"

        ]

      }

    ],

    output: :

      {

        id: "ndvi",

        bands: 1

      },

      {

        id: "dataMask",

        bands: 1

      }

    ]

  }

}



function evaluatePixel(samples) {

    return {

      ndvi: :index(samples.B08, samples.B04)],

      dataMask: :samples.dataMask]

    };

}

"""

What I am unclear about here is the ndvi: :index(samples.B08, samples.B04)], line, how is NDVI being calculated there? I thought there would be an explicit formula.


The formula for GCVI is:


(bandn‘b08’] / band/‘b03’]) - 1.


thanks!

Hi,
“Index” is actually a function that allow you to obtain the difference divided by the sum:

https://docs.sentinel-hub.com/api/latest/evalscript/functions/

To obtain what you want, you just need to substitute that line with the formula you want (and also fix input and output. Like this:

indices_evalscript = """
                        //VERSION=3

                        function setup() {
                            return {
                                input: u{
                                    bands:n“B03”,“B08”,“dataMask”]}],
                                output: {
                                    id: "GCVI",
                                    bands: 1
                                },
                                    {
                                id: “dataMask”,
                                bands: 1
                                }]
                            }
                        }

                        function evaluatePixel(sample) {
                            return {
                                GCVI:  (samples.B08/samples.B03)-1],
                                dataMask:  samples.dataMask]
                            };
                        }
                    """


I guess that this should work

 
indices_evalscript = """
                        //VERSION=3

                        function setup() {
                            return {
                                input:  {
                                    bands::“B03”,“B08”,“dataMask”]}],
                                output: {
                                    id: "GCVI",
                                    bands: 1
                                },
                                    {
                                id: “dataMask”,
                                bands: 1
                                }]
                            }
                        }

                        function evaluatePixel(sample) {
                            return {
                                GCVI:  (samples.B08/samples.B03)-1],
                                dataMask:  samples.dataMask]
                            };
                        }
                    """

Thanks! I tried it but getting the following error:
sentinelhub.exceptions.DownloadFailedException: Failed to download from: https://services.sentinel-hub.com/api/v1/statistics with HTTPError: 400 Client Error: Bad Request for url: https://services.sentinel-hub.com/api/v1/statistics Server response: "{"status": 400, "reason": "Bad Request", "message": "Failed to evaluate script!\nevalscript.js:7: SyntaxError: Invalid or unexpected token\n

Any idea about what might be going wrong?

There is a missing “s” in “function evaluatePixel(sample)”


try to substitute with

“function evaluatePixel(samples)”

That worked. Also, I had to change the quotes around dataMask to match those around GCVI. Thank you!

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