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I have coe in GEE that calcultes the NDVI in a given polygon, from 2000 (based on landsat 7) and 2019 (landsat 8) ,create for each one a layer with pixels that their NDVI value is higher than 0.3 and then subtract them from each other in order to detect change.

The problem is that when I run my code for some reason the result is that ther is no diffference and I believe I have problem in my code. I think mabybe GEE doesn't do the subtruction if the pixels are not on the same location so I always get that no change.

maybe it will be easier to understand from my code: https://code.earthengine.google.com/98102459e86cc67232896d226f19565b

Basically I have create to layers in a long process and in this specific line:

// Map.centerObject(geometry,10);
for (var i in listOfNumbers1){
  var imageNDVI1 = ee.Image(listOfImages.get(listOfNumbers[i]));
  var hot2019=imageNDVI1.gt(0.3)
  .selfMask()
  .rename('hotspot03');
Map.addLayer(hot2019,{palette: '0000ff'},'2019');}

and then I subtract the two layers (hot2000 and hot 2010) like this:

var difference=hot2019.subtract(hot2000);

Map.addLayer(difference,{min:-1, max:1 ,palette: ['ff3300', 'a3a375','009933']},'difference');

My end goal is to get new layer that will be calssified into 3 values: -1,0 and 1

*I thought maybe the reason it happened is because it doesn't have rectangle extent *Any polygon would work. I have checked Delhi and New Mexico

  • Please, try to recreate this problem with a minimal script. Right now, it's a lot of code, making it hard to help you. – Daniel Wiell Jan 1 at 19:52
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I didn't follow all your steps, but I did notice one error when you add a map layer:

Map.addLayer(hot2019,{palette: '0000ff'},'2019');

When you have a palette with one single color, that's the color you will get on your map, no matter what value you have. In your case, you have three discrete values: -1, 1, 1, so you'd want to provide three colors in your palette.

This could maybe give you some ideas:

https://code.earthengine.google.com/8f6e883e6bd03a8f413eab5aa19a269d

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