Hello,
I'm currently running a TMS tile server generating geotiff tiles from DEM data
which I'm consuming with the GDAL TMS driver using an XML file along the
following lines:
<GDAL_WMS>
<Service name="TMS">
<ServerUrl>http://localhost:8080/terrain/${z}/${x}/${y}.tif</ServerUrl>
</Service>
<DataWindow>
<UpperLeftX>-20037508.34</UpperLeftX>
<UpperLeftY>20037508.34</UpperLeftY>
<LowerRightX>20037508.34</LowerRightX>
<LowerRightY>-20037508.34</LowerRightY>
<TileLevel>20</TileLevel>
<TileCountX>1</TileCountX>
<TileCountY>1</TileCountY>
<YOrigin>top</YOrigin>
</DataWindow>
<Projection>EPSG:3857</Projection>
<BlockSizeX>256</BlockSizeX>
<BlockSizeY>256</BlockSizeY>
<DataType>Float32</DataType>
<BandsCount>1</BandsCount>
<MaxConnections>50</MaxConnections>
<ZeroBlockHttpCodes>204,404,500</ZeroBlockHttpCodes>
</GDAL_WMS>
This all works perfectly except for the fact that the responses interpreted as
<ZeroBlockHttpCodes> are filled with a default value of 0. This obviously isn't
great for elevation data :) Ideally I'd like to be able to specify a fill or
NODATA value somewhere in the XML, something like:
<GDAL_WMS>
...
<NoData>-9999</NoData>
or
<FillValues>-9999</FillValues>
...
</GDAL_WMS>
The contents of a <NoData> tag might be a comma separated list for multiband
rasters.
Would an enhancement request to support this be acceptable? Otherwise can
anyone suggest any workarounds for the issue?
My current thoughts are that I could generate zero filled tiffs and return
those instead of 404 responses, and wrap the TMS XML with a VRT that assigns an
appropriate NODATA value. This is far from ideal however, as there are a lot of
potential 404s and generating data for this is wasteful in terms of processing
and bandwidth.
Best regards,
Homme
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