[GRASS-user] r3.in.ascii - Difficulties understanfing format

[Nikos Alexandris]

Tom, my apologies for writing something long, and repeat within the text
some times things already mentioned or known. I did so on purpose --
just to practice and see if I understand the concept myself.

Ah, please keep in your posts Cc to the grass-user mailing list. Others
will definitely benefit from our mistakes or the correct examples we
discuss.

On Tue, 2009-01-13 at 15:13 +0100, tom at vdputte.nl wrote:
> Hi Nikos,
> 
> Thanks for the quick response!
> So what I gather from your answer is that the region-definitions are
> set seperately (I'm guessing in the mapset?) and that you can only
> display data that falls within the boundaries of this region?

Correct. Just to make the big picture clear:

Location = One coordinate system > Many mapsets with separate region
settings for each.

In addition, an important and very useful characteristic of GRASS'
raster modules (r.*) is that they operate *only* within the defined
region.


> The my problem transforms a bit,in the sense that I want to display a
> 3D array/raster. Ultimately, this needs to be georeferenced, but for
> testing purposes I just want to display this raster in Nviz.

> So how can I create a general Mapset in which I can display a 3D
> raster with a resolution of 1 (e.g North-South, E-W and T-B all 3 - 0
> with a raster of 3x3x3)

If you have non-georeferenced spatial data you can create a generic XY
location and set the region to match the extent of your imported (in the
xy location) raster no-matter how big/small it is.

[see [1][2] and search on the mailing list [3] for how to create an xy
location -- it's a "standard" question when one starts to explore data
with grass]

# set region
g.region rast=YourRaster -p
# or: "g.region rast=YourRaster -pa" ## read "g.region help" for more

It should, I think, obtain automatically the required rows & columns
parameters which should correspond to the columns & rows of your raster.
If not just grab the resolution of your raster somehow (e.g. "gdalinfo
YourRaster) and set them manually.

I think that "south & north" should match columns & rows. "east & west"
are irrelevant and, I think, you can set the latter to 0.

Hmmm... talking about 3D I think the correct term is voxels, and hence
you can set the vertical resolution to 1 as well. But you can experiment
with whatever you think you need...

The important, in order to *see* your data is here the (x=)columns,
(y=)rows and (z=)levels.

Now, the *how* they will appear will be affected by the defined x,y,z
resolution.

Since the units in an XY location are pixels it's correct to set the
resolution to 1.


A few more notes concerning "georeferenced" maps/locations

While the resolution of the georeferenced map itself is as is (let's say
you have the CORINE land cover of some European country, the raster
version of 250m pixel size), and refers to the units used by the defined
coordinate system, the resolution you define with g.region will affect
the output of most raster processing modules.

# corine_250m
# match region-extent to the "corine_250m" map
g.region rast=corine_250 res=500 -pa

# produce a 500m corine map
r.mapcalc corine_500m=corine_250m
# so simple ;-)

> I hope you understand my problem. 
> Thanks, Tom
[...]

I hope I helped you with my bla-bla. Cheers, Nikos

---
[1] http://grass.itc.it/grass62/manuals/html62_user/helptext.html
[2] http://n2.nabble.com/Re%
3A-GRASS-user--Help-with-reprojection-td2104056.html#a2107019

[3] http://n2.nabble.com/Grass---Users-f1837860.html