[GRASS5] New GIS Manager adds transparency to layers

[Michael Barton]

I¹ve just finished phase 2 of the GIS Manager update and it¹s pretty
exciting. At first glance, it looks a lot like the one I¹ve been working on
and have in the CVS now, but with a couple of important exceptions. One is
that transparency is now supported for all GRASS layers.

The second will probably generate the most discussion, so I¹m ready to duck
and run for cover.  Now GRASS is consistent with other GIS programs and more
intuitive (as much as I am skeptical about that term) in that the uppermost
layer in the layer tree is also the top map in the display. Related to this,
new layers insert directly above the currently selected layer instead of at
the bottom of the layer tree.

The main changes come Œunder the hood¹ of this version of the GIS Manager.
It uses g.pnmcomp to composite a set of maps (each rendered as *.PPM files)
into a visual display. One of the results is that now GRASS is significantly
faster in adding new layers, turning layers on and off, and changing layer
attributes‹only the new or changed layer needs to be rendered; the others
will just be re-composited into a display from existing PPM files. This all
happens in a GRASS .tmp directory, so that it doesn¹t clutter up your home
directories. The other important thing about this new architecture is that
it makes GRASS even less dependent on the xdriver and PNGdriver for
visualization. GRASS can become more easily portable to different OS¹s and
GUI frameworks. It is also more scriptable. You can write a script that will
create a complete, multilayered map, and output it to a graphics file.

One consequencer of this new architecture is that the GIS Manager does not
currently support display output to PNG files. With GDAL (required for many
GRASS features) and ghostscript installed, it does support output to
PPM/PNM, TIF, JPG, BMP, EPS, and PDF.

Command line usage is still supported  in several ways‹the old xterminal is
still there, there is the new command console, and you can add command
layers to the layer tree and display them.

You can see a screen shot of semi-transparent soil vector areas overlaying a
raster shaded relief map at

http://www.public.asu.edu/~cmbarton/files/grass_screenshots/gism2-2.jpg

I¹ve committed all changes to the CVS. For those of you with binary versions
of GRASS who would like to try it, I¹ve posted packages you can use to
replace your current GIS Manager on my website. For full functionality, you
need a version of grass that is dated 21-February-2006 or later. For those
of you with a slightly earlier version, I made a second package with all
functionality minus transparency. Here are the links.

New GIS Manager files

<http://www.public.asu.edu/~cmbarton/files/grass_gismgr/gism_rc4_20060307.tg
z>

New GIS Manager files for people with recent, but pre-21 February 2006
binaries.

<http://www.public.asu.edu/~cmbarton/files/grass_gismgr/gism_rc4_20060307pre
_02-21.tgz>

Enjoy
Michael

______________________________
Michael Barton, Professor of Anthropology
School of Human Evolution and Social Change
Arizona State University
Tempe, AZ  85287-2402
USA

voice: 480-965-6262; fax: 480-965-7671
www: http://www.public.asu.edu/~cmbarton

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