It took a little debugging (the ultimate documentation), but the answer is to
add:
PROCESSING "OVERSAMPLE_RATIO=1" # the default is 2!
PROCESSING "LOAD_FULL_RES_IMAGE=NO"
to the layer in map file.
Best Regards,
Brent Fraser
Brent Fraser wrote:
James,
Did you find a solution to this problem? I'd like to use OSM tiles in
Mapscript to create an image for server-side creation of large format
PDFs for printing, and found that mapserver+GDAL does not calculate the
best TileLevel based on the output extents and image size.
For example, in my XML file I have:
<TileLevel>15</TileLevel>
When using gdal_translate:
gdal_translate -projwin -12412016 7714617 -12384098 7693893 -outsize
1461 1084 frmt_wms_osm_tms.xml test.tif
GDAL requests Level 13 images, and produces a great looking image.
However Mapserver's shp2img:
shp2img -e -12412016 7693893 -12384098 7714617 -s 1461 1084 OSM.map -o
test.png
requests Level 14 (too high a resolution); many more tiles are requested
and down-sampled, and the image is un-readable.
Best Regards,
Brent Fraser
James Perrins wrote:
I've been trying to use Open street map tiles via a mapserver WMS
service displayed in OpenLayers.
This is sort of working - in that I'm getting maps displayed and they
seem to be in the right position (as checked against other datasets).
My issue is that the images are nowhere near as clear as the originals
from the Open Street map tiles. I've kept projections the same
throughout - and they don't appear to be being re-projected. The
images saved in the local cache (if enabled) are the same as from Open
Street Map. What appears to be happening is that mapserver is getting
images from (perhaps) a zoom level too high - and then re-sampling
these to produce the WMS output image - which then appears to have too
much detail displayed for its zoom level (if you understand what I'm
trying to say).
Any ideas why this is happening - I've messed around with Bounding
boxes and image sizes - but it doesn't seem to make any difference.
Thanks
James
MapFile extract:
LAYER
NAME "OSM"
STATUS ON
TYPE RASTER
DATA "D:\Websites\OpenStreetMap\OSM.xml"
PROJECTION
"init=EPSG:900913"
END
END
<GDAL_WMS>
<Service name="TMS">
<ServerUrl>http://tile.openstreetmap.org/${z}/${x}/${y}.png</ServerUrl>
</Service>
<DataWindow>
<UpperLeftX>-20037508.34</UpperLeftX>
<UpperLeftY>20037508.34</UpperLeftY>
<LowerRightX>20037508.34</LowerRightX>
<LowerRightY>-20037508.34</LowerRightY>
<TileLevel>19</TileLevel>
<TileCountX>1</TileCountX>
<TileCountY>1</TileCountY>
<YOrigin>top</YOrigin>
</DataWindow>
<Projection>EPSG:900913</Projection>
<BlockSizeX>256</BlockSizeX>
<BlockSizeY>256</BlockSizeY>
<BandsCount>3</BandsCount>
</GDAL_WMS>
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