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I have this situation on Google Earth Engine: 3 different images, each of these are made by 17 different bands. These bands represent the different year. I call these images with these letter: a,b and c. Image c is a binary map (1, no data). I would like to have a map that answer to this condition:

if b > b+1= a(b∩c) else a+1(b+1∩c)

for example if the values of a band of 2000 are major than 2001 the map respect this condition else l'altra. I consider only the year and the next year (2000-2001,2002-2003 ....)

So I would if the condition is true the only pixel of a or a+1 image that respect the intersect condition. I did some tests using only 3 bands (one per image) and I identified this possible solution in this command:

a.updateMask(b).updateMask(c)

But how I can do for respect my condition?

I think to an expression as the following code:

a.expression(‘?b>b+1=a.updateMask(b).update(c): a+1.updateMask(b).updateMask(c)’,
{‘a’:a.select(),‘b’:b.select(),‘c’: c.select() })

I obtain this error message:

Image (Error)
Image.parseExpression: Expression parse error at character 0:
'? b(y)>b(y+1) = a(y).updateMask(b(y)).updateMask(c(y)):  a(y+1).updateMask(b(y+1)).updateMask(c(y))'
 ^.

Where am I doing wrong?

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Your expression is not stated well. With access to the assets, this seems to be a fast solution:

var list = ee.List.sequence(0,15,1);
var mapA = ee.Image('users/mattelearning85/mapA');
var mapB = ee.Image('users/mattelearning85/mapB');
var mapC = ee.Image('users/mattelearning85/mapC');
var mapC ee.Image('users/mattelearning85/mapC').select(['b1','b2','b3','b4','b5','b6','b7','b8','b9','b10','b11','b12','b13','b14','b15','b16','b17','b18'], ['b0','b1','b2','b3','b4','b5','b6','b7','b8','b9','b10','b11','b12','b13','b14','b15','b16','b17'])

var images = ee.ImageCollection.fromImages(list.map(function(y) {
  y = ee.Number(y).toInt();
  var a = mapA.select(y).rename('a');
  var a1 = mapA.select(y.add(1)).rename('a1');
  var b = mapB.select(y).rename('b');
  var b1 = mapB.select(y.add(1)).rename('b1');
  var c = mapC.select(y).rename('c');

  var b_gt_b1 = a.updateMask(b.gt(b1)).updateMask(b).updateMask(c);
  var b1_lte_b = a1.updateMask(b.lte(b1)).updateMask(b).updateMask(c);

  return b_gt_b1.blend(b1_lte_b).set('imageNumber', y);
}));

print(images);
Map.addLayer(images);

link

  • Sorry, the assets are public now (I think) here the script following your indications code.earthengine.google.com/91e0b060559ee7f083912a4b84dba25b the script function but in b1_lte_b image should not I use the image a1? – Matpec33 Jan 12 at 8:14
  • Yes it needed to be a1. Thanks for giving the access. I updated the answer. I guess you will need blend instead of add, as otherwise all masked pixels will be omitted. – Kuik Jan 12 at 8:57
  • thank a lot for your help, sorry for my delate. I found some errors into start data in particular for map C. Following your suggestion I introduce some little device to to the script (I update the script). why the use of blend function? – Matpec33 Jan 16 at 19:27

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