I have a list of features containing two Polygons that belong to a MultiPolygon feature:
var polygon_lst = ee.Feature(MP_feat).geometry().coordinates(); //MP_feat is a MultiPolygon
I want to take every element of this list(two polygons), calculate their corresponding polygon.area() and return the index of the element whose polygon has the maximum area.
I think I need to use reducers at some point but I am not sure how. Any comment on this?
Here's how I would approach this problem.
Get a list of geometries from the MultiPolygon. This will be easier to deal with than a list of lists of coordinates.
var polygon_list = MP_feat.geometries();
Get a corresponding list with the area of each polygon using a map. Note that you need to specify a maxError when calculating area.
var area_list = polygon_list.map(function(f) {return ee.Geometry(f).area(1)});
Calculate the largest area in the list using a max reducer.
var largest_area = areas.reduce(ee.Reducer.max());
Get the index of the largest area identified above. Because the area list corresponds to the polygon list, this is also the index of the largest polygon.
var largest_index = area_list.indexOf(largest_area);
Optionally, get the largest polygon using the index.
var largest_polygon = ee.Geometry(polygon_list.get(largest_index));
Here's a script to demonstrate with some dummy data: https://code.earthengine.google.com/2100c0f01bf74e5a101b1f162de5cf58.
