[GRASS-dev] ps.map: raster always under vector map?

[Glynn Clements]

Markus Neteler wrote:

> >>> Bear in mind that the raster map is always opaque, so it will obscure
> >>> anything which is drawn beneath it.
> >>>       
> >> Markus:
> >>     
> >>> That's exactly what I need: in my case the raster map contains a few
> >>> cells only, but I need it on top to not be covered by vector contour
> >>> lines etc.
> >>>       
> >> ..
> >>     
> >>> Maybe ps.map's raster command needs an additional parameter "ontop" or
> >>> something like this? Hacking C code as Hamish suggests might be asked
> >>> too much for the average user.
> >>>       
> >> are the null areas solid white, not transparent?
> >>     
> >
> > They are transparent. All fine.
> Of course I was too hasty. Nothing fine.
> > Just that the tons of contour
> > lines cover the scarse raster areas in the raster maps. That's
> > why I need them on top of the dense contour lines.
> >   
> ... and it seems that NULL is not respected by ps.map (as you will know
> already).

For masked images, you need to use the one-operand form of the "image"
operator with an image dictionary; see the RASTERMASK procedure in
lib/psdriver/psdriver.ps for an example. This requires support for
level 3 PostScript (present in GhostScript for a few years now; I
don't know about printers).

Regarding the generation of the image data (ps/ps.map/ps_raster.c), a
masked image needs 2 (mono) or 4 (RGB) components, with the mask byte
first (i.e. AARRGGBB); see lib/psdriver/Raster.c.

-- 
Glynn Clements <glynn at gclements.plus.com>