[Xastir] transparency?

[Curt, WE7U]

On Wed, 6 Oct 2004, Rick Green wrote:

>   So I'm on to the next level in this learning curve.  Map layers and
> transparency.  WHat I'm seeing is that I can overlay Michigan.pdb on top
> of (Higher layer number) any raster image, but I can't seem to get any
> raster map to overlay another raster map.  The background color, usually
> white, seems to totally obscure the underlying raster.  I see in the .geo
> files that there is a parameter called 'TRANSPARENCY' which is set to
> white in the distributed file, but I still get the white background
> obscuring the underlying raster.  Mebbe it's not quite white?  How can I
> determine what specific value is in those pixels?
>   Also, Terraserver seems to have a problem, in that if even one pixel of
> the current view is not available, terraserver gives me no image at all.
> Unfortunately, there appears to be a skinny N-S stripe just east of my
> home that's missing in their database.  I don't think that's an xastir
> problem, but it sure would be nice if they would deliver an image with the
> missing pixels transparent, so a toposerver image could show thru.
>
>   I'd like to be able to have the USRadar image overlay terraserver, which
> overlays toposerver, with the simple Michigan.pdb vector map on top of all
> that.  But without transparent backgrounds, all I see is one raster source
> with one vector map on top.
>   The GEO file for tigermap is much simpler, and it has its own
> configuration dialog.  Is there a way to give it a transparent background,
> too?

Don't want much, do you?

The "special" .geo's which only have a single tag in them are due to
the fact that we have to compute the URL on the fly before we
request the image.  We have no facilities in there as far as I know
for transparency, although you could try adding the TRANSPARENCY tag
in there to see if it gets parsed in the generic code anyway.  It
might.

As far as overlaying raster images on top of other raster images,
that is generally considered a no-no, except when you're talking
about our special case of radar with a transparent background.

I usually select exactly zero or one raster images as my bottom
layer, then it's fine to layer vector maps, radar images, and
weather alerts on top of that.  If you select more than one raster
image, you'll end up obscuring large parts of the lower images with
the upper images.  Perhaps if we had a way to do multiple
transparent colors we could knock out more of the filled areas, but
generally it's a bad idea.  It's also slow using raster maps, plus
they don't scale well.

My advice would be to get used to using vector maps instead.  In
order to do what you're wanting above, try this:

Use terraserver for the base image (raster)
Overlay USGS DLG contour files in SDTS format (need GDAL/OGR library)
Overlay the PDB file on top of that.

This will give you the satellite images, the contour lines, and the
PDB maps all-in-one.  To see what the contours look like on top of
satellite images, see the Search and Rescue Features link off
www.xastir.org.

--
Curt, WE7U			         http://www.eskimo.com/~archer
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