[mapserver-users] Selective Background Transparency with Labels

[thomas bonfort]

On Fri, Feb 13, 2009 at 16:16, Bob Basques <Bob.Basques at ci.stpaul.mn.us> wrote:
> Bill,
>
> I understand (I think what you're after.  The only way I can figure out how to do this would be with three images stacked on top of each other.
>
> You would generate the background first,
> then build the contour lines separately,
> lastly, the labels, which would be drawn with the contours again but the contours would be drawn over the labels with the same color as the background (transparent color).
>
> Stacking these all together I think will get you the desired effect.
>
> You would need something like GeoMoose or openlayers to view the stack though.
>
> bobb
>
>
>
>>>> thomas bonfort <thomas.bonfort at gmail.com> 02/13/09 8:37 AM >>>
> If I correctly understand what you're trying to do, then no, this is
> not possible with mapserver, as this would require recovering the
> pixels that have been overdrawn by the line.
>
> regards,
> thomas
>
> On Fri, Feb 13, 2009 at 15:14, Bill Thoen <bthoen at gisnet.com> wrote:
>> Is there a way to set a LABEL BACKGROUNDCOLOR to render transparent just
>> pixels of a particular color instead of changing all pixels to the specified
>> color? My situation is regarding contour line labels. I want the label to
>> follow the contour line's center, but I would like just the parts of the
>> contour line behind the labels to be knocked out, leaving the background
>> otherwise untouched.  In this case the color of the layer just below the
>> contour lines varies across the map (it's a shaded relief layer), so setting
>> BACKGOUNDCOLOR to a specific value doesn't give me the effect I want. Any
>> solutions?
>>
>> - Bill Thoen
>>
>>
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