Google Earth Engine: Clip ImageCollection with a grid (FeatureCollection) into several segments

Question

I want to clip an ImageCollection with a grid (FeatureCollection) in Google Earth Engine. Every image in the ImageCollection should be clipped with every feature in the FeatureCollection. I need all images as separate segments for further calculations. Therefore, the result should be a new ImageCollection with each image segment including all properties of the original ImageCollection.

I work with Sentinel-1 images (SAR) and generated a grid over my study area. The clipping between the ImageCollection and the grid works (see Code snippet or the link for the GEE script). My problem is that I don't know how I can address the several image segments now for further processing.

var imagecollection = Sent1;
var featurecollection = grid;

var clip_fc = function(col) {
return col.clipToCollection(featurecollection);
};
var map_ic = imagecollection.map(clip_fc);

print ('New ImageCollection:', map_ic);
Map.addLayer(map_ic, imageVisParam, 'New ImageCollection');

https://code.earthengine.google.com/479120ce6641a2e49f1f728fb9150806

Does anyone have an idea? I'm not that advanced with JavaScript and short explanations or links would be very helpful as well!

Answer 1

You can create a function that take as arguments both the image and feature collections and then loop over all the entries of each object using map. Additionally, you need to make a small trick to convert the FeatureCollection coming from the feature collection loop to an ImageCollection and flatten the resulting ImageCollection.

// Function to loop over image and feat collections
var wrap = function(imagecol, featcol){
  // image collection loop
  var resul = imagecol.map(function(image){
    // feature collection loop
    var resul2 = featcol.map(function(feat){
      // make clip and add feat property according to feat id
      return ee.Image(image).clip(ee.Feature(feat))
                            .set({
                              'feat': ee.Feature(feat).id()
                            });  
    });
    // convert the FeatureCollection to list and convert it to ImageCollection
    return ee.ImageCollection.fromImages(resul2.toList(featcol.size()));
  });
  // Flatten, unnest lists
  return ee.ImageCollection(resul.flatten());
};

// Apply function
var map_ic = wrap(imagecollection, featurecollection);

print ('New ImageCollection:', map_ic);

// Add layers
Map.addLayer(ee.Image(map_ic.first()), imageVisParam, 'New ImageCollection');
// Select another image using the feat property
Map.addLayer(ee.Image(map_ic.filter(ee.Filter.eq('feat', '-9,119'))
                            .first()), 
                            imageVisParam, 
                            'New ImageCollection');