Pixel value display

yes that’s what i did, but it gives me 3 different values. I’m using the NDVI layer, and I need to know the ndvi value in a certain pixel

Hello,

If you are using the latest version of the plugin with an updated version of QGIS, you can access the pixel values via the Identify features tool. See the screen-shot below (tool circled in red):

The tool opens a side pane where you can unroll the layer name and get the values (out1, out2, out3, etc…) in a table.

Ah, I understand. That is because you are creating a layer that returns a visualisation of NDVI (in the Red, Green and Blue channels) and not the actual NDVI values. If you want NDVI values, I would recommend to add a layer in your dashboard (along-side other layers) where you call the NDVI values. When you create the layer you can access some pre-made templates, including the “raw” NDVI. Under set Custom Script.

Otherwise you can copy this script for your layer:

//VERSION=3

function evaluatePixel(samples) {
    let val = index(samples.B08, samples.B04);
    return [val, samples.dataMask];
}

function setup() {
  return {
    input: [{
      bands: [
        "B04",
        "B08",
        "dataMask"
      ]
    }],
    output: {
      bands: 2
    }
  }
}

When queried in QGIS, you get out1 = NDVI and out2= Datamask.

Alright, I will try this and get back to you. Thank you so much

the problem is there aren’t the colors I want in the visualization options

Hello again,

No problem: the visualisation options are just templates that we made for the most common cases. You can create any visualisation that you want (almost) by writing it yourself in the Custom script editor. Here is the page with the documentation on how to write different types of visualisation so that you can display the data exactly as you want.

Maxim

how can I add this color visualization:

const visualizer = ColorGradientVisualizer.createRedGreen(0.0, 1.0);
visualizer.process(0.0); // returns [ 0.8431372549019608, 0.0980392156862745, 0.1098039215686275 ]
visualizer.process(0.3); // returns [ 0.992156862745098, 0.5764705882352941, 0.5764705882352941 ]
visualizer.process(0.5); // returns [ 0.9058823529411765, 1, 0.2352941176470588 ]
visualizer.process(0.8); // returns [ 0.5450980392156863, 0.7686274509803922, 0.2666666666666667 ]
visualizer.process(1.0); // returns [ 0.0705882352941176, 0.4627450980392157, 0.0392156862745098 ]

// Returns ColorGradientVisualizer
// ColorRampVisualizer

To this NDVI script:

//VERSION=3
    function setup() {
      return{
        input: [{
          bands: ["B04", "B08"]
        }],
        output: {
          id: "default",
          bands: 1,
          sampleType: SampleType.FLOAT32
        }
      }
    }
    function evaluatePixel(sample) {
      let ndvi = (sample.B08 - sample.B04) / (sample.B08 + sample.B04)
      return [ ndvi ]
    }

??
PS. I don’t have a background in Coding or Web, that’s why my questions may sound dumb 😛

A visualiser takes values and maps them to RGB colours. Therefore the first step is to return 3 bands (or 4 if you want to make noData areas transparent).

Then you can call the visualiser and you are done 🙂

In the following scripts you can tailor the bounds of the data (0.0 and 1.0) to tweak the visualisation range.

For 3 bands:

//VERSION=3
function setup() {
  return{
    input: [{
      bands: ["B04", "B08"]
    }],
    output: {
      id: "default",
      bands: 3,
      sampleType: "AUTO"
    }
  };
}

// Map NDVI from Dark Green to White (between 0 and 1): adjust to liking
const visualizer = ColorGradientVisualizer.createWhiteGreen(0, 1.0);

function evaluatePixel(sample) {
  // Calculate ndvi
  let ndvi = (sample.B08 - sample.B04) / (sample.B08 + sample.B04);
  
  // Return color mapped NDVI (0 to 1)
  return visualizer.process(ndvi);
}

An example here.

For 4 bands (3 bands + transparency):

//VERSION=3
function setup() {
  return{
    input: [{
      bands: ["B04", "B08", "dataMask"]
    }],
    output: {
      id: "default",
      bands: 4,
      sampleType: "AUTO"
    }
  };
}

// Map NDVI from Dark Green to White (between 0 and 1): adjust to liking
const visualizer = ColorGradientVisualizer.createWhiteGreen(0, 1.0);

function evaluatePixel(sample) {
  // Calculate NDVI
  let ndvi = (sample.B08 - sample.B04) / (sample.B08 + sample.B04);
  
  // Get color mapped NDVI (0 to 1)
  let ndvi_vis = visualizer.process(ndvi);  
  
  // Return colormap + nodata mask as transparency
  return [ndvi_vis[0], ndvi_vis[1], ndvi_vis[2], sample.dataMask];
}

An example here: notice outside the orbit, the data is no longer white but transparent.

But when I return 3 bands i lose again the ndvi values. How can I have the ndvi value in the output while having the colors I want please?

This is not possible to “pack” in the 3-band layer. You could output 4-band, where first three bands would represent colors and the fourth one NDVI value. But then you would probably have a hard time finding software that can read this.

It probably makes sense to create two layers - one with colors and one with values.

And how could I output 4-bands, where first three bands would represent colors and the fourth one NDVI value?

Something along these lines:

//VERSION=3
function setup() {
  return{
    input: [{
      bands: ["B04", "B08", "dataMask"]
    }],
    output: {
      id: "default",
      bands: 5,
      sampleType: "FLOAT32"
    }
  };
}

// Map NDVI from Dark Green to White (between 0 and 1): adjust to liking
const visualizer = ColorGradientVisualizer.createWhiteGreen(0, 1.0);

function evaluatePixel(sample) {
  // Calculate NDVI
  let ndvi = (sample.B08 - sample.B04) / (sample.B08 + sample.B04);
  
  // Get color mapped NDVI (0 to 1)
  let ndvi_vis = visualizer.process(ndvi);  
  
  // Return colormap + nodata mask as transparency
  return [ndvi_vis[0], ndvi_vis[1], ndvi_vis[2], ndvi, sample.dataMask];
}

I tried it but it doesn’t work

Can you explain a bit more into details on what you have tried and what it means “it does not work”?
If we are to help you, we need to understand your steps to the level that we can repeat them.

As mentioned above: “But then you would probably have a hard time finding software that can read this.”

Sentinel Playground, along with most other web GIS applications expects the tiles to be 3-band, providing information about “red”, “green” and “blue”. Sentinel Hub services can provide mutli-band output, but you will need to develop your own software to read these results. Sentinel Playground is not one of these.

AH now I understand. Alright, thank you so much for your help 🙏