Hi Everybody,
Thanks to all your suggestions, I have solved the performance problem. It was a
combination of two things: rendering in 24bit and MapServer reprojecting on the
fly when I didn't want it to.
I modified my OUTPUTFORMAT block to be:
OUTPUTFORMAT
NAME "png"
DRIVER AGG/PNG
IMAGEMODE RGB
MIMETYPE "image/png"
EXTENSION "png"
FORMATOPTION "QUANTIZE_FORCE=ON"
FORMATOPTION "QUANTIZE_DITHER=OFF"
FORMATOPTION "QUANTIZE_COLORS=256"
END
I tested the time taken for the Quantize method for WMS and MapServer layers at
a specific test location:
QUANTIZE NO QUANTIZE GD/PNG PC256
WMS 17.44s 28.93s 17.10s
MapServer 10.55s 26.41s 8.91s
GD/PNG PC256 is the fastest, but this gives incorrect colours.
Next, i changed the projection string to the epsg code (as suggested by
Guillaume):
PROJECTION
"init=epsg:3034"
END
QUANTIZE, with epsg code
WMS ~10.5s
MapServer ~10.5s
The ironic thing is that I used the projection string instead of the epsg code
so I could avoid the lookup so it would be faster! I do not understand why
MapServer does an unnecessary reprojection with OpenLayers.WMS and the
projection string; shouldn't it be able to determine that the projection string
is the same as the epsg number? I guess, that would probably involve a lookup,
thus rendering the use of the projection string in place of the epsg code
ineffectual.
Thanks again for all the help, it would have taken me much longer to solve the
problem on my own!
Regards
John Westwood
Great Britain Historical GIS Project
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