Classifying an image based on the EVI values of vegetation

Question

I am very new at GEE, and I’m trying to classify an image based on the EVI range of various vegetation classes. For example, Bamboo may have a minimum threshold of 0.6712 and maximum of 0.776 EVI. This way I have 10 classes. I obtained the EVI band from my Landsat image.

How do I classify the pixels and assign them values from 1-10 for the 10 classes?

I tried using ee.Algorithms.If method:

    var EVIband = ee.Image(CFL598.select('EVI'));
    print("evi", EVIband);
    Map.addLayer(EVIband, {min:-0.10, max:0.8, bands:['EVI']}, 'EVI Band');

    var ten = ee.Image(ee.Algorithms.If((EVIband.gte(0.6712).and(EVIband.lte(0.776))), EVIband.mask(ee.Number(10))));
    print("bamboo", ten);
    Map.addLayer(ten);

I was planning to do this for the rest of the 9 classes and use addBands to create a whole image, but this did not work.

Answer 1

EVIband.gte(0.6712).and(EVIband.lte(0.776) evaluates each pixel and returns 1 if the pixel value meets the conditions and 0 if not. If you want to give the pixels that meet this condition some identifiable number, easiest is to multiply this image by a constant ee.Image. Example:

var ten = EVIband.gte(0.6712).and(EVIband.lte(0.776).multiply(ee.Image(10))

I agree, I would sum over all the binary images to get a final class band. If you define a list of thresholds beforehand, it is possible to map a function over this list, rather than adopt a brute-force apprpoach. Example segmenting an EVI image (EVIband) into three classes:

var T1 = ee.List([0,0.3,0.6]) // define lower thresholds 
var T2 = ee.List([0.3,0.6,0.9]) // define upper thresholds 
var key = ee.List([1,2,3]) // unique "key" to assign to each class 

var classband = ee.ImageCollection.fromImages(
  
  // map over list of indices 
  ee.List.sequence(0,T1.length().subtract(1)).map(function(index){

    // return binary image 
    return EVIband.gte(ee.Number(T1.get(index)))
      .and(EVIband.lt(ee.Number(T2.get(index))))
      .multiply(ee.Image.constant(key.get(index)))
      .toUint16()
    })
  )

   // sum over all images 
  .sum() 

EDIT for completeness, example of brute-force approach:

var one = EVIband.gte(0).and(EVIband.lt(0.3)).toUint16()
var two = EVIband.gte(0.3).and(EVIband.lt(0.6)).multiply(ee.Image(2)).toUint16()
var three = EVIband.gte(0.6).and(EVIband.lt(0.9)).multiply(ee.Image(3)).toUint16()
var classband = ee.ImageCollection.fromImages([one,two,three]).sum()

which is actually less code than the previous example but, maybe not as elegant for the case of having 10 classes.