Extract geometry from feature not working?

Question

This works:

(with geometry being a Polygon and sent3 an ImageCollection):

var image = sent3.filterBounds(roi).first();
var mask = image.select("Oa07_radiance").mask().rename('mask');
var area = ee.Image.pixelArea().multiply(mask).rename('area');

var sumDictionarypolygon1 = mask.addBands(area).reduceRegion({
  reducer: ee.Reducer.sum(),
  geometry: roi,
  scale: 300,
  maxPixels: 1e9
});
print('sum for pol 1 mask, scale=300', sumDictionarypolygon1);

While this does not (roi being a Feature containing a geometry)

var rois = ee.FeatureCollection("users/guillaumh/embalsescba"),
    sent3 = ee.ImageCollection("COPERNICUS/S3/OLCI");
var roi = rois.toList(99).get(26);
print(roi);

var image = sent3.filterBounds(roi).first();
var mask = image.select("Oa07_radiance").mask().rename('mask');
var area = ee.Image.pixelArea().multiply(mask).rename('area');

var sumDictionarypolygon1 = mask.addBands(area).reduceRegion({
  reducer: ee.Reducer.sum(),
  geometry: ee.Geometry(roi),
  scale: 300,
  maxPixels: 1e9
});
print('sum for pol 1 mask, scale=300', sumDictionarypolygon1);

The error is:

Dictionary (Error)
Feature, argument 'geometry': Invalid type. Expected type: Geometry. Actual type: Feature.

Why cannot I extract the geometry from the feature? It seems ee.Geometry( ) does not do anything.

Answer 1

First, instead of ee.Geometry(roi) (which in this case is essentially "assume this is already a Geometry", which it isn't), you need to use ee.Feature(roi).geometry(), which returns the geometry of the feature.

Second, you modified your call to reduceRegion but you also wrote filterBounds(roi), which also needs a Geometry rather than a Feature.

Therefore, try this:

var roi = ee.Feature(rois.toList(99).get(26)).geometry();

Then both of the places you use roi will work.