[OSM-dev] request for hosting of WMS layers

Jukka Rahkonen jukka.rahkonen at mmmtike.fi
Tue Mar 16 11:50:17 GMT 2010


jamesmikedupont <at> googlemail.com <jamesmikedupont <at> googlemail.com> writes:

> 
> Lets see:The russian toplogical maps 24G 
...But they are converted to tiffs so much bigger. 
I guess we could go back the ECW proprietary compressed jpeg.. 
but that needs special drivers.

ECW is a fine format but it is a bit unclear if the license allows to use it for
free on the server side even as an input image. It is probably OK but nobody
seems to know for sure. What is sure is that it is not allowed to 
send out ecw from a server without ECW SDK license from Erdas.

If disk space is a problem a rather good alternative is to use jpeg compression
inside tiff. Mapserver works pretty fast with such tiff images. The command to
use is like this:

gdal_translate -of GTiff -co COMPRESS=JPEG -co PHOTOMETRIC=YCBCR -co TILED=YES
-co JPEG_QUALITY=85 input.tif output.tif

However, both ecw and jpeg compression gives some problems if images are warped
and have nodata areas which are often written out as totally black or white
pixels. After compression nodata areas are no longer uniformly black and marking
pixels with RGB value of 0 0 0 as transparent does not work. As a result there
will be some amount of very dark but not totally black pixels which will remain
visible. However, this can be avoided by doing some mosaicing and cutting before 
compression. I can give some advice if needed, but perhaps OSM-dev is not the
most suitable place for that. 

-Jukka Rahkonen-





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