[mapserver-dev] Need mapfile for AGG and Transparent overlay

[Stephen Woodbridge]

Thomas,

When I display the the map as the base map I want antialiasing on so the 
map looks smooth. But for a transparent overlay, I do not want 
antialiasing on because it creates lots of artifacts along the edges of 
lines in a transparent image.

What I have done in the past is create two mapfiles one for AGG that is 
antialiased and another that I run through GD that does not have 
antialiasing in it. This is a lot of extra work.

The reason I have been doing this is that the GD renderer does(did?) not 
not understand things like WIDTH, you had to use a SYMBOL and SIZE to 
stroke the roads.

Maybe I've had my head too buried in projects to notice that things have 
changed in which case I would be happy to be enlightened :) otherwise my 
request is that we try to drive the renderers to support a common 
mapfile language/behavior and/or to the extent that they support it 
allow transparency/antialiasing to be switched on/off.

My goal is to get this into your thinking and planning, because I 
realize it is likely not a small task, but I think it would have high 
value to users if they can trivially switch between antialiased maps to 
transparent overlays using the same mapfile and change a few parameters 
and layers on/off.

Thanks,
   -Steve W

Thomas Bonfort wrote:
> Steve,
> Why would you want aliased output?
> Why isn't RGBA+quantization sufficient in your case?
> 
> best regards,
> thomas
> 
> www.camptocamp.com
> +33 5 16 57 01 02
> 
> 
> 
> On Wed, Nov 4, 2009 at 22:20, Stephen Woodbridge
> <woodbri at swoodbridge.com> wrote:
>> Thomas,
>>
>> I think this is mostly directed at you. I have been using your sample OSM
>> mapfile and it is really great - Thanks for putting this together.
>>
>> It raises an issue that I think needs to be dealt with, but maybe I'm
>> missing some feature that is already implemented.
>>
>> My use case is that I need a single mapfile that I can use for antialiased
>> rendering like your file above, but I also need to generate transparent
>> overlay images of just the road network by selecting just those layers or
>> group. For example, in Openlayers, I need to have google like controls for
>> [map][hybrid][etc] where the [map] view is like above and the hybrid view is
>> satellite imagery as an OL layer and transparent road network overlay in OL.
>>
>> So it would be nice if we can use a single mapfile to do both.
>>
>> In OL, I would set the overlay layer to be:
>>  imagetype: 'png',
>>  transparency: 'on',
>>  antialias: 'off',
>>  ...
>>
>> or whatever and then the mapfile would be interpreted correctly for
>> generating a non-antialiased transparent image.
>>
>> Questions:
>>
>> 1. Can this be done now? or do I need to build a separate mapfile for these
>> two tasks?
>>
>> 2. Does this sound like a reasonable goal? Achievable in 6.0?
>>
>> 3. There were some posts that hinted that you might be trying to obsolete
>> the gd rendering code, which I do not have a problem with. How would this
>> impact this issue?
>>
>> I hope this all makes sense.
>>
>> Thanks,
>>  -Steve W
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