Google Earth Engine – How to Reproject

coordinate systemgoogle-earth-engine

var L8 = L8.filterBounds(geometry).first()
Map.addLayer(L8,{max:3000},'Before Reprojection')
var proj = ee.Projection('EPSG:4326').getInfo()
var L8r = L8.reproject(proj.crs,proj.transform)
Map.addLayer(L8r,{max:3000},'After Reprojection')

A reprojection to EPSG:4326 would be benefictial. But after Reprojecting, the Image seems Oddly Broken into 3 Large Pixles.

Adding a Picture Manifactured from the Projection will result in much more then 3 Pixels an a usefull looking resolution :
var coordspic = ee.Image.pixelCoordinates(ee.Projection('EPSG:4326')).select('x') Map.addLayer(coordspic,{max:2,min:-7},'Coordinates')

What am I missing here ?

Best Answer

that is because you did not define a scale for the reprojection. If you would print the scale at which the projection you defined by default, you understand why the image is plotted in three large pixels:

// Specify a projection
var proj = ee.Projection('EPSG:4326');
print('Scale projection == reason for three blocks', proj.nominalScale()); // 111319.49079327357

To set the projection in a scale you find resonable (30m for landsat images), you can reproject by defining a scale:

var L8r = L8.reproject(proj, null, 30)
Map.addLayer(L8r, {min: 0,  max:3000, bands: ['B4', 'B3', 'B2']}, 'After Reprojection')

The link to your code was invalid, so I defined the Landsat collection and geometry myself: Link

Related Solutions

GDAL – Fixing Holes Between Imagery Tiles Projected Using gdalwarp

Creating a mosaic from your source images takes only a few seconds if you use GDAL virtual raster as output. Read

http://www.gdal.org/gdal_vrttut.html and http://www.gdal.org/gdalbuildvrt.html

Often the artifacts like you have can also be avoided by taking care that the individually warped images are aligned to use a common canvas. This can be achieved by using -tap parameter together with -tr parameter. I would try that first. Read about -tap from http://www.gdal.org/gdalwarp.html

Google Earth Engine – Reprojecting Vector FeatureCollections

Not sure if transforming vector is worth it, but here's the trick.

According to docs, .transform() is ony applied to an ee.Feature, not ee.FeatureCollection. So you have to map the procedure over a FeatureCollection.

// Define an arbitrary region in which to compute random points.
var region = ee.Geometry.Rectangle(-119.224, 34.669, -99.536, 50.064);

// Create 1000 random points in the region.
var randomPoints = ee.FeatureCollection.randomPoints(region);

// Display the points.
Map.centerObject(randomPoints);
Map.addLayer(randomPoints, {}, 'random points');


var dst_projection = 'EPSG:3857';


// Apply transformation
var transformer = function(a_feature) {
  var transformed_feature = a_feature.transform(dst_projection, 0.001);
  return transformed_feature;
};

var points_prj = randomPoints.map(transformer);

print(points_prj);

This is a link to the snippet on EE

Best Answer

Related Solutions

GDAL – Fixing Holes Between Imagery Tiles Projected Using gdalwarp

Google Earth Engine – Reprojecting Vector FeatureCollections

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