[GIS] Google earth engine: filter a FeatureCollection by system id

filtergoogle-earth-engine

I have a FeatureCollection in Google Earth Engine, where each Feature is referenced by an id tag. How do I filter the FeatureCollection based on that id?

Following attempts to filter id=3 did not work:

 // Create a FC (from https://developers.google.com/earth-engine/guides/feature_collections)
var features = [
  ee.Feature(ee.Geometry.Rectangle(30.01, 59.80, 30.59, 60.15), {name: 'Voronoi'}),
  ee.Feature(ee.Geometry.Point(-73.96, 40.781), {name: 'Thiessen'}),
  ee.Feature(ee.Geometry.Point(6.4806, 50.8012), {name: 'Dirichlet'})
];
var FC = ee.FeatureCollection(features);
print(FC, "FC")

// extract basedon ID?
print(FC.filter(ee.Filter.eq("id", 2)))
print(FC.filter(ee.Filter.eq("system:id", 2)))

Best Answer

This is tricky, as there are actually two issues:

It's called system:index even though the UI shows it as id.
The id is a string, rather than an integer

So the correct way to do this is:

print(FC.filter(ee.Filter.eq("system:index", '3')))

Your Code

These lines don't seem to work out:

var dateFilter = ee.ImageCollection(longRain2016.merge(shortRain2016).merge(longRain2017).merge(shortRain2017).merge(longRain2018));

var s2dateFilter = s2.filter(dateFilter);

You are trying to construct another ee.ImageCollection passing existing ImageCollections to it. According to the API, this won't work.

I also think that it is not necessary to achieve what you want because ee.ImageCollection.merge returns an ImageCollection anyway.

This should work:

var allSeasons = longRain2016.merge(shortRain2016).merge(longRain2017).merge(shortRain2017).merge(longRain2018);

Now, since you already should have a merged ImageCollection of all the seasons in allSeasons, you don't need the second step. (Actually this wouldn't work because your dateFilter object is not a Filter and filter() only accepts a Filter.)

You can simply proceed with var count = allSeasons.size();

Alternative way ("The Multiple-Filter-Method")

You could first create the Filters and then Filter.or()-join them together. Next you could apply this joint Filter to the ImageCollection:

//Create Filters
var longRain2016Filter = ee.Filter.date('2016-04-01','2016-05-31');
var shortRain2016Filter = ee.Filter.date('2016-11-15','2016-12-31');
var longRain2017Filter = ee.Filter.date('2017-04-01','2016-05-31');
var shortRain2017Filter = ee.Filter.date('2017-10-01','2016-12-31');
var longRain2018Filter = ee.Filter.date('2018-03-01','2018-05-31');

var allSeasonsFilter = ee.Filter.or(longRain2016Filter, shortRain2016Filter, longRain2017Filter, shortRain2017Filter, longRain2018Filter); // Create joint Filter

var allSeasons = s2.filter(allSeasonsFilter); //apply Filter to ImageCollection

Google Earth Engine – Dissolving FeatureCollections for Efficient Data Management

Your simplest solution is the following.

 var joinedFeatures = DMDP.union()
 Map.addLayer(joinedFeatures)

Then set the colours that you prefer before adding it to the map.

Best Answer

Related Solutions

Google Earth Engine Filter – Applying Multiple Date Filters in Google Earth Engine

Your Code

Alternative way ("The Multiple-Filter-Method")

Google Earth Engine – Dissolving FeatureCollections for Efficient Data Management

Related Question