[GIS] Creating opacity mask in Google Earth Engine

google-earth-enginelandsatmaskingopacity

I have an NDSI snow layer loaded in Google Earth Engine. Since snow is present for values <0.4, I want to make values >0.4 opaque. I looked at the manual's examples, but this code is not giving me what I want. Instead I get black (<0.40) and white (>0.40).

What am I missing?

var winter = NDSI.filter(ee.Filter.calendarRange(1999,2018,'year')).filter(ee.Filter.calendarRange(6,8,'month'));
var medianWinter = winter.median();
var medianWinterMask = medianWinter.gt(0.4);
Map.addLayer(medianWinterMask);

Best Answer

To mask an image, use the method ee.Image.updateMask(). Masking is also covered in the Introduction to the Earth Engine JavaScript API tutorial.

There are many ways to present masked data, but here is one possibility using the variables from your example code:

Map.addLayer(medianWinter.updateMask(medianWinterMask), {min:0, max:100});

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[GIS] Mask clouds in an ImageCollection google earth engine

Based on the answer of Mask clouds in LandSat 8 surface refletance image, one possibility is:

NOTE: replace YOUR_PLACE with a Geometry or Feature

// Filter the collection
var col = ee.ImageCollection("LANDSAT/LC8_SR")
          .filterDate("2016-01-01", "2016-12-31")
          .filterBounds(YOUR_PLACE)

// Mask clouds
var col_noclouds = col.map(function(img) {
                   var mask = img.select(['cfmask']).neq(4)
                   return img.updateMask(mask)
                   })

// Median image
var median = ee.Image(col_noclouds.median())

// NDVI
var median_ndvi = median.normalizedDifference(['B4', 'B5'])

[GIS] Google Earth Engine Mask application

When you select the QA band, the QA image has only one band (you selected one image). Applying a function expression on that image with other band numbers than zero is not possible, because there is only one band in that image, thus:

// Select the QA band.
  var QA = image.select('ET_QC');
  var cloud = getQABits(QA, 3, 4, 'cloud_state')
                        .expression("b(0) == 1 || b(0) == 2"); // sélection des deux bits que l'on dégage

AND

  // Select the QA band.
  var QA = image.select('ET_QC');
  // Get the internal_cloud_algorithm_flag bit.
  var qscore = getQABits(QA, 5, 7, 'quality score')
                        .expression("b(0) == 2 || b(0) == 3 || b(0)==4"); // sélection des deux bits que l'on dégage

Link code

Best Answer

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[GIS] Mask clouds in an ImageCollection google earth engine

[GIS] Google Earth Engine Mask application

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