Transparency in WMS

[Daniel Morissette]

Jacolin Yves wrote:
> Le Tuesday 07 August 2007 14:37:59 Daniel Morissette, vous avez écrit :
>>
>> If you are using MapServer as a WMS service and expecting the
>> transparency/opacity of a given layer to result in a 50% opaque GetMap
>> response then that won't work.

...

> 
> Is it a limitation from mapserver or from the standard itself?
> 

It's a bit of both.

The WMS spec is not clear on whether it is acceptable to return 
semi-transparent images. Section 7.2.3.9 of the WMS 1.1.1 spec talks 
about the TRANSPARENT=TRUE/FALSE GetMap parameter but that is only to 
control whether the background of the image is fully transparent or not 
and does not address the possibility of producing semi-transparent 
images. Everywhere else it suggests that pixels representing features 
are fully opaque.

And it may also be a MapServer limitation in the sense that we may need 
to make some changes to allow MapServer to generate semi-transparent 
images... but maybe not and that works already, I just haven't checked.

Daniel
-- 
Daniel Morissette
http://www.mapgears.com/