[Qgis-user] map collars

[MS]

I realize this goes into other software on a qgis list, but I wonder  
with GDAL or GRASS one can accomplish this.

It is really a raster clip that would work well, especially if the  
next step is mosaic'ing the rasters.  Are these quad maps?

Mark

On Mar 18, 2009, at 3:28 PM, "John C. Tull" <john.tull at wildnevada.org>  
wrote:

> Although, this approach can be problematic if white is important for  
> properly displaying the map information. E.g., USGS topographic maps  
> use a white background for the map and a white collar. My solution  
> was to hand select the collar in Gimp, make it a unique color  
> (magenta or something), then apply the transparency to that color.  
> This is not fun if you have many maps to work with.
>
> John
>
> On Mar 18, 2009, at 4:17 AM, Paolo Cavallini wrote:
>
>> Chris h ha scritto:
>>
>>> No apology necessary. Map collars are the white borders around  
>>> maps that are
>>> typically distributed from governmental sources in raster format.  
>>> In order to
>>> stitch or glue charts together you need to remove the collars.  
>>> (white area)
>>
>> Oh, that can be easy: for displaying purposes, just set the white  
>> value
>> to null, in the raster properties dialogue. If you want to  
>> permanently
>> set the white to NULL, you can use gdal for this.
>> All the best.
>> -- 
>> Paolo Cavallini: http://www.faunalia.it/pc
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