CODEWITHSUNDEEP
google-earth-engine
joel
joel

Reputation: 11

Filtering out images from imageCollection with high cloud percentage(sentinel-2). This returns 0 elements?

I'm running an image collection through an NDWI function. I'm trying to filter out images with a lot of clouds. Sentinel-2 has the metaData CLOUD_PIXEL_PERCENTAGE, and I was hoping I could filter for images less than a certain cloud pixel percentage(say 10-20%). For some reason this returns zero images, no matter the value I use, so I must be using the function incorrectly. 

var bands = ['B11','B8','B3'];
var collection = ee.ImageCollection('COPERNICUS/S2').select(bands);
var filtered = collection.
filterBounds(geometry4).
filterDate('2017-05-01','2017-12-01');

var filterClouds
=filtered.filter(ee.Filter.lt('CLOUD_PIXEL_PERCENTAGE',100));
print(filterClouds);

I'm using the ee.Filter.lt object, which should return images with values that are less than the specified value(100) for the specified metaData(Cloud Pixel Percentage). I should be returning practically all the images? but I'm returning none...

can I not run ee.Filter.lt on an ImageCollection? if so, is there a similar function used for collections?

Upvotes: 0

Views: 4453

Answers (1)

Val
Val

Reputation: 7023

The metadata property you need is called CLOUDY_PIXEL_PERCENTAGE, so you're filtering on a non-existing entry which doesn't return an error, but no results either.

Also, ImageCollections have a built-in method, called filterMetadata which achieves the same result you get, but without the need to specify a ee.Filter:

var geometry4 = ee.Geometry.Point(-107.42, 36.63)

var bands = ['B11','B8','B3'];
var collection = ee.ImageCollection('COPERNICUS/S2').select(bands);

var filtered = collection
.filterBounds(geometry4)
.filterDate('2017-05-01','2017-12-01');

var filterClouds = filtered
.filterMetadata('CLOUDY_PIXEL_PERCENTAGE','less_than',50);

// returns 21 results
print(filtered.size())

Upvotes: 1

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