[GIS] Downscaling raster images in Google Earth Engine

google-earth-engineinterpolation

How can I downscale raster images using basic interpolation methods in Google Earth Engine?

For example, I want to resample Landsat image from 30m to 10m, but I cannot find corresponding functions in Google Earth Engine. Right now there are only 'resample' (cannot change the spatial resolution) and 'reduce_resolution' functions there.

Does anyone know something about it?

Best Answer

You can control the pixel size of an image by setting the scale parameter of ee.Image.reproject():

// Reference a Landsat scene.
var image_30m = ee.Image('LANDSAT/LC08/C01/T1/LC08_044034_20170614');

// Define visualization parameters for a true color image.
var vizParams = {'bands': 'B4,B3,B2',
                 'min': 5000,
                 'max': 30000,
                 'gamma': 1.6};
Map.addLayer(image_30m, vizParams, 'image_30m');

// Get the projection information for a band.
var band2 = image_30m.select('B2');
print('CRS:', band2.projection().crs());

// Display a bilinear resampled image with 10m pixel spacing.
var image_10m = image_30m.resample('bilinear').reproject({
  crs: band2.projection().crs(),
  scale: 10
});
Map.addLayer(image_10m, vizParams, 'image_10m');

If you want even more control over the projection, you can manually change the CRS transform (crsTransform) parameter:

// Reference a Landsat scene.
var image_30m = ee.Image('LANDSAT/LC08/C01/T1/LC08_044034_20170614');
// Define visualization parameters for a true color image.
var vizParams = {'bands': 'B4,B3,B2',
                 'min': 5000,
                 'max': 30000,
                 'gamma': 1.6};
Map.addLayer(image_30m, vizParams, 'image_30m');

// Get the projection information for a band.
var band2 = image_30m.select('B2');
var proj = band2.projection().getInfo();
print('CRS:', proj.crs);
print('original CRS transform:', proj.transform);

// Construct a new CRS transform, using 10m spacing.
var transform_new = [
  10,
  proj.transform[1],
  proj.transform[2],
  proj.transform[3],
  -10,
  proj.transform[5],
];
print('new CRS transform:', transform_new);

// Display a bilinear resampled image with 10m pixel spacing.
var image_10m = image_30m.resample('bilinear').reproject(
  {
  crs: proj.crs,
  crsTransform: transform_new
});
Map.addLayer(image_10m, vizParams, 'image_10m');

See the Projections doc page for more information.

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