[GRASSLIST:7427] Re: [GRASS5] Voxels/3D rasters in GRASS 6.1

[Michael Barton]

Benjamin,

I got 3-D points to display in NVIZ pretty readily. I was testing this out
several months ago. I suppose that it still works OK, but haven't tested it
lately. The thing that tripped me up for awhile was the fact that my z-scale
(total range of a couple meters) was much less than my xy scale (range of a
couple hundred meters). I had to greatly increase the z exaggeration to see
the 3D points.

For voxels, I had more trouble. I got the Slovakia dataset to work well
once, but not a second time. However, this was several months ago and it may
work better now. Again, there are some tricks. In the case of voxels, you
need to set the isosurfaces to values that actually show something. I did
this by trial and error, but you should be able to do this more
intelligently with some practice.


(Without checking) I think that all voxel commands are now under the r3.*
designation. I don't know why the information you are seeking is missing,
except to say that the true 3D functions are still relatively rough and
experimental compared with the 2D/2.5D in GRASS (as they are in other GIS's
if they are even present at all).

Hope this is helpful.

Michael


On 7/1/05 2:50 AM, "benducke at compuserve.de" <benducke at compuserve.de> wrote:

> This is another mail in my desperate quest for handling 3D data
> in GRASS. I am trying voxels this time and got stuck just as
> quickly as with 3D vectors.
> Maybe someone could answer some of the questions I have.
> I am using GRASS 6.1 CVS (about 2 weeks old).
> 
> 1. Do all commands that relate to voxels have r3. prefix now? Which
> other commands relate to voxels?
> 
> 2. r3.in.ascii mentions s.to.rast3 is there an equivalent command for
>    this in 6.1?
> 
> 3. When trying to visualise a voxel in nviz, I get:
> 
>   Illegal filename. character <> not allowed.G__open(r): mapset (benni)
> doesn't    match xmapset (ô¯@DHäÿ¿|v at 5&òr@ÿÿÿÿ@äÿ)
> 
>   on the console. Am I using a broken version of nviz?
> 
> 4. Why does r3.info not give information about the data range?
> 
> 5. How do I get actual volume information, do I have to count the
>    non NULL cells in the voxel map, then add them up? Is there
>    any command that can give me 3D raster voxel statistics?
> 
> 6. Is there any CURRENT information about voxels and GRASS on the
>    web?
> 
> I would be very happy indeed about any information on this subject!
> 
> Cheers,
> 
> Benjamin
> 
> 
> 
> 

____________________
C. Michael Barton, Professor of Anthropology
School of Human Evolution and Social Change
PO Box 872402
Arizona State University
Tempe, AZ  85287-2402
USA

Phone: 480-965-6262
Fax: 480-965-7671
www: <www.public.asu.edu/~cmbarton>