How to get total average ndvi please

1

Hi

i would like to know how can i adapt the below posted evalscript to obtain the total average ndvi
evelscript:

// Script to extract a time series of NDVI values using 
// Sentinel 2 Level 2A data and  metadata file.
function setup() {
    return {
      input: [{
        bands: ["B04", "B08"],
        units: "DN"
      }],
      output: {
        bands: 1,
        sampleType: SampleType.FLOAT32
      },
      mosaicking: Mosaicking.ORBIT
    }
    
  }

  
  function evaluatePixel(samples) {
    // Precompute an array to contain NDVI observations
    var n_observations = samples.length;
    let ndvi = new Array(n_observations).fill(0);
    
    // Fill the array with NDVI values
    samples.forEach((sample, index) => {
      ndvi[index] = (sample.B08 - sample.B04) / (sample.B08 + sample.B04) ;
    });
                       
    return ndvi;
  }
2

Hi @burkhard.golla ,

To obtain the mean NDVI of your area of interest, please have a look at our Statistical API and the example requests.

3

thanks, but will the evalscript remain as it is as shown in my question or it should be changed as well?

4

Hi @burkhard.golla ,

In this example you will find the Evalscript. You just need to change the output from a single band reflectance to the NDVI index.

5

but to find the ndvi we need two bands, red and NIR?right?

6

Yes, you can still have two input bands and calculate the NDVI. The only thing different is that you output should be the NDVI index instead of the single band reflectance.

7

would you please adapt the evalscript posted in my question with the neede change?i want to be sure that i am doing it the correct way please

8 
//VERSION=3
function setup() {
  return {
    input: [{
      bands: [
        "B04", "B08", "dataMask"
      ]
    }],
    output: [
      {
        id: "ndvi", bands: 1
      },
      {
        id: "dataMask", bands: 1
      }
    ]
  };
}

function evaluatePixel(samples) {
    let index = (samples.B08 - samples.B04) / (samples.B08+samples.B04);
    return {
        ndvi: [index],
        dataMask: [samples.dataMask]
    };
}
9

appreciate it, many thanks

10

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