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I need to export tiles from a WMTS server to the MBTiles format. The server is not public, but I have access to it and permission to export a specific portion of the tiles. The problem I have seems to come from the different projections:

  • The WMTS server uses UTM zone 38N (EPSG:23038)
  • The exported MBTiles needs to be in WGS84 spherical mercator (EPSG:3857)

What's the easiest approach to achieve this, and with which tools?

I already tried loading the WMTS source in QGIS and using QTiles. This works, but the resulting tiles are rendered poorly, I guess due to a sub-optimal reprojection algorithm.

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I've been able to get this to work using MapProxy. MapProxy is a powerful tool for cases like this, because it allows you to define everything through a configuration file instead of having to click through a UI.

MapProxy supports raster re-projection and various storage formats including mbtiles.

The individual steps to export a certain area are as follows:

  • configure the data source as source and test it through the MaprProxy stand-alone server
  • define a cache in the same projection as the source
  • define a second cache with the target projection, use the first cache as source
  • define the area that should be exported as polygon (e.g. GeoJSON)
  • add the GeoJSON to the seed configuration as coverage
  • define a seed task for the second cache using the specified coverage

Now run the seed task. When it is finished, the exported mbtiles file can be found in the cache_data directory.

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