[GRASS5] Gaussian filter for GRASS -- second service

Jachym Cepicky jachym.cepicky at centrum.cz
Fri Apr 22 10:00:42 EDT 2005

Hallo developers,
so I gave it some more time and tryed to work in all the comments from Glynn
and I hope, I can say, GRASS has its own Gaussian filter.

The module handels all the maps as DCELL map, it uses scrolling window
(scrolling rows), like r.neighbors or r.grow2 and it hopefully frees all the

The first version, I posted into this list, is really bad and I would suggest
all of you, not to look at the code, it could hurt to your electronic cardiac

I would like, if some one could have a look at the code, like Glynn did, and to
tell me, what one (me) could do better or if there is no bigger bug. It would
be very important for me, as this is the first modul, I wrote, and even first

Comparison with r.mapcalc implementation:
nsres:      0.5
ewres:      0.5
rows:       3332
cols:       3413

r.mapcalc                           |
(gaussian.pl at GRASS add-ons site):| r.gauss:
real    0m26.534s                   | real    0m8.482s
user    0m24.281s                   | user    0m7.787s
sys     0m0.898s                    | sys     0m0.437s

Which means, it is really faster :-)

Why did I write standalone module and why didn't I merge it with e.g.

1) I wanted to learn, how to write own modules in GRASS (this was the most
   importand for me)

2) Gaussian filter needs parametr sigma on it's input - none of methods from
   r.neighbors needs any other parametr - it would be unconsistent.
3) I hope to write some other tools for remote sensing. All the filters need
   special parametres, so I personaly don't see the way, how to merge them into
   one (two) big module(s) :-/
   Gaussian filter is the simplest filter. I wrote it more from study reasons,
   as that I would really need it for my work. But it is mentioned, as the
   basic low pass filter.

I don't stand on, put my r.gaussian into CVS-tree. It can live on the GRASS
add-ons site (if not somewhere else). I would just please someone to check
my work, if there is someone who could give it some time ... sometimes :-)

Thank you

Jachym Cepicky
e-mail: jachym.cepicky at centrum.cz
URL: http://les-ejk.cz
GPG: http://www.fle.czu.cz/~jachym/gnupg_public_key/
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