[gdal-dev] GDAL WMTS Driver - How do you control the Tile Matrix Set's Tile Level?

[esacree]

I am trying to use the new GDAL_WMTS driver with GDAL Version 2.1.  
Problem:  The thread that receives the data from the server gets a GDAL data
set handle with a total data buffer size of 4,294,967,296 for a 4 band
image.

Questions:  
1.	 Does GDAL_WMTS driver return all tiles combined into a single image
memory buffer?  
2.	Is the data buffer returned for WMTS retrieved the same way as for WMS
with a call to the GDAL Data Set rasterio function?
3.	Is there any way to control which tile level in the TileMatrixSet is
returned for GDAL_WMTS?   A TileLevel tag is in the GDAL_WMS XML definition
http://www.gdal.org/frmt_wms.html  but not in the GDAL_WMTS
definition/example http://www.gdal.org/frmt_wmts.html 

According to the returned data parameters, the image is huge 32K x 32K x 4
with around 4GB of memory needed to create a 4 band image.  The area
requested is a fairly small area around the Cumberland River.

Here’s a sample of the Service Request sent to the WMTS server.  The XML is
similar to the request generated by GDAL_Translate for the server.  The
DataWindow coordinates are much smaller and in range of the server’s data. 
Request coordinates were converted from EPSG:26926 to EPSG:3857 for the
request shown below.

<GDAL_WMTS>     
<GetCapabilitiesUrl>http://basemap.nationalmap.gov/arcgis/rest/services/USGSShadedReliefOnly/MapServer/WMTS/1.0.0/WMTSCapabilities.xml</GetCapabilitiesUrl>
        <Layer>USGSShadedReliefOnly</Layer>
        
        <TileMatrixSet>default028mm</TileMatrixSet>
    <DataWindow>
        <UpperLeftX>-9664344.849763</UpperLeftX>
        <UpperLeftY>4328551.472775</UpperLeftY>
        <LowerRightX>-9646502.672226</LowerRightX>
       <LowerRightY>4318753.685277</LowerRightY>
    </DataWindow>
    <BandsCount>4</BandsCount>
    <Cache />
    <UnsafeSSL>true</UnsafeSSL>
    <ZeroBlockHttpCodes>204,404</ZeroBlockHttpCodes>
    <ZeroBlockOnServerException>true</ZeroBlockOnServerException>
</GDAL_WMTS>

With the exception of the DataWindow parameters, the request matches the
test request generated by GDAL_Translate for the server.  The DataWindow 
values are well within the full range of the WMTS Server for the requested
layer.

Thanks in advance!

Elaine




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