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Resolve "Add AggregateImageSource to combine several image sources into one"

Sébastien Guimmararequested to merge
581-aggregate-image-source into main

Summary

This MR introduces the AggregateImageSource, which, similarly to the AggregatePointCloudSource, combines several sources into one.

const source1 = new GeoTIFFSource({ url: 'http://example.com/image1.tif' });
const source2 = new GeoTIFFSource({ url: 'http://example.com/image2.tif' });

const aggregate = new AggregateImageSource({ sources: [source1, source2] });

Features

  • Supports ordering sources by z-index (the index of the source in the array is the z-index)
  • Can mix any type of sub-source (geotiff, vector, wmts, etc), as long as they have the same image parameters (see below)
  • All sub-sources must have the same CRS

Advantages

By combining sources into a single source, we avoid the need to create multiple layers. This is useful for the following reasons:

  • Workaround the limitation of a single elevation layer per Map
  • Workaround the limitation of a single color layer per point cloud
  • Massively reduce the memory footprint of layers (no need to create additional render textures)
  • Reduce the CPU footprint of layers

Inconvenients

Using sources rather than layers gives less control over the images:

  • cannot change the opacity of individual sources
  • cannot assign different colormap to individual sources
  • all sources must share the same parameters, such as flip-y, datatype (cannot mix 8-bit and 32-bit images), color space
  • all sources must have the same CRS (though we might want to support per-source reprojection later)

Use cases

Possible use cases include:

  • Stacking WMS/WMTS/vector layers into a single layer, useful to compose a full image from thematic layers (orthophoto, roads, administrative subdivisions...)
  • Combine a low-resolution elevation source, such as ETOPO, SRTM, GEBCO, and high-resolution local elevation sources, such as GeoTIFFs
  • Compose a mosaic of images, such as a mosaic of SRTM tiles (a bit like the now-deleted CustomTiledImageProvider, but much more flexible, since it can support any kind of sub-source)
  • Mimic a GDAL VRT file

TODO

  • Upload datasets to 3d.oslandia.com
  • Improve description of example
  • Add stacked WMTS layers example
  • Add SRTM mosaic example
  • Add stacked elevation sources (low-res + high-res) example
  • Add documentation to AggregateImageSource
  • Expose AggregateImageSource to API documentation
  • Add basic tests for AggregateImageSource
  • Support stacking transparent sources (e.g WMTS layers)
  • Handle abort errors in requests

Closes #581 (closed)

Edited by Sébastien Guimmara

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