[GIS] Exporting an image in Google Earth Engine image alignment

exportgoogle-earth-engine

When I export an image in Google Earth Engine the resulting raster does not match the original. When I import the export back into Google Earth Engine the is an spatial misalignment between the original (orange in picture below) and the exported version (green in the picture below). The direction as size of the misalignment varies across the image. A solution appears to be to set the scale of the image below its native resolution, in this instance 1m as opposed to 30m; however this will hugely increase the size of the image. Am I missing something in the export call

Export.image.toDrive({
  image: landsat,
  description: 'imageExport',
  scale: 30,
  crs: 'EPSG:3857',
  maxPixels: 800000000000
});

Best Answer

If you export by specifying a scale for Landsat images, you are explicitly overriding the non-integer affine transform with an integer one, and introducing a 1/2 pixel shift.

You may want to try Exporting with the original image.projection() instead of creating a new one from scratch.

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[GIS] Exporting a classified map from google earth engine

How to export an image to Google Drive using the Earth Engine Code Editor:

Add some javascript code that exports an image to the Code Editor window. (I have added a few variable assignment statements to make it a working example.)

    var classified = ee.Image('USGS/NLCD/NLCD2011').select('landcover');
    var geometry = ee.Geometry.Polygon(
        [[[-122.58, 38.23],
          [-122.58, 37.79],
          [-121.85, 37.79],
          [-121.85, 38.23]]]);
    Export.image.toDrive({
      image: classified,
      description: 'imageToDriveExample',
      scale: 30,
      region: geometry
    });

Click the Run button to execute the code.
Select the Tasks tab, if it is not already selected. You should see a task named "imageToDriveExample" with a grey background indicating that the task has not been run.
Click the Run button to the right of the task. A dialog box will appear with the parameters that will be used for the export. If needed, update the export parameters. (I like to specify a Drive Folder that I previously created for exports, for keeping things organized.)
Click dialog box's Run button to start the task. Note that the Run button is replaced with a spinning gear icon, which indicates the task is running.
Wait for the task to complete. Once it completes, the task becomes blue and the spinning gear icon will be replaced with a checkmark.
To show information on a completed task, place your cursor over the task name and click on the question mark. This will bring up a dialog box with information about the task, including a link named "Output link".
Click on the "Output link" which opens up the Google Drive folder that you specified earlier.

For additional details on export options, see the Earth Engine documentation page Exporting Data.

[GIS] Resampling in Google Earth Engine: exporting Sentinel 1A to Google Drive

If you want to export the original image, set the crs, crsTransform and dimensions parameters to match the values of the original image. Setting the scale value may get you similar results, but scale is a less direct specification of the coordinate reference system (CRS).
If a different CRS is specified (using the scale or crs and crsTransform parameters), Earth Engine selects the nearest scaled image from the asset's image pyramid, and resamples (using nearest neighbor by default) as necessary. See the Scale documentation page for more details.

For even more details, see the Projections, Resampling and Reducing Resolution and Exporting Data pages of the Earth Engine documentation.

Best Answer

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[GIS] Exporting a classified map from google earth engine

[GIS] Resampling in Google Earth Engine: exporting Sentinel 1A to Google Drive

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