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(Cloud-Optimized) GeoTiffs in the Web Editor

What is required by back-ends to give users an ideal experience with GeoTiff imagery in the Web Editor?

  1. All GeoTiffs must be valid GeoTiffs (including all required metadata) and should be valid cloud-optimized (COGs). If the files are not exported as COGs, the Editor needs to read the whole GeoTiff file at once which will usually fail with larger files (> 10 MB).
  2. Range requests must be supported by the server to allow reading COGs.
  3. CORS must be sent by the server providing the files, especially you need to allow Range headers in Access-Control-Expose-Headers additionally.
  4. COGs should provide overviews in the files whenever the files get larger than 1 or 2 MB in size. The overview tiles should have a size of at least 128x128 pixels and at maximum 512x512 pixels.
  5. The GeoTiff must be readable by geotiff.js, especially the data type and the compression must be supported.
  6. The GeoTiff metadata in the file should contain:
    1. The no-data value in TIFFTAG_GDAL_NODATA, if applicable
    2. A projection, via the "geo keys" ProjectedCSTypeGeoKey or GeographicTypeGeoKey (otherwise provide at least a unit in ProjLinearUnitsGeoKey or GeogAngularUnitsGeoKey)
    3. GDAL metadata should be provided in the tag TIFFTAG_GDAL_METADATA per band:
      1. Minimum and Maximum values (tags: STATISTICS_MINIMUM and STATISTICS_MAXIMUM)
      2. A band name (tag: DESCRIPTION)
    4. The PhotometricInterpretation of the image should be set to 1 (BlackIsZero) if an RGB interpretation is not clear. If RGB is set as interpretation (2) and you have more than 3 samples per pixel (SamplesPerPixel), the ExtraSamples should be set.
    5. ColorMaps are supported.
  7. For batch jobs, the STAC metadata is recommended to contain per asset:
    1. The no-data value either in file:nodata (deprecated) or in nodata in bands
    2. The minimum and maximum values per band in the statistics object in bands
    3. A band name in bands
    4. The projection in proj:code (recommended), proj:wkt2 (not well suported by OpenLayers) or proj:proj4 (deprecated by STAC)
    5. The type must be set to the corresponding media type (see below)
  8. For synchronous execution, the Content-Type in the header of the response must be set to the corresponding media type (see below)

Links to the corresponding STAC extensions:

  • eo
  • file (v1.0.0, latest is v2.1.0 but doesn't support nodata any more)
  • proj
  • raster

Media Types:

  • COGs (image/tiff; application=geotiff; cloud-optimized=true)
  • GeoTiffs (image/tiff; application=geotiff)