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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