[GRASS-user] nviz - thematic mapping for vector points

Nikos Alexandris nikos.alexandris at felis.uni-freiburg.de
Mon Jul 27 15:42:58 EDT 2009

I have problem understanding nviz settings for 3d vector points (Vector
Points Panel).

I have some point data (converted to 3D vector) and columns x, y, z,
annual (fp precipitation values), annual_int (integer precipitation
values), etc.

I want to get the spheres coloured based on z (elevation) and sized
(=volume) based on the precipitation values upon the srtm3_dem. Hence, I
use the "thematic mapping for vector points". No matter what I try, I
don't it right.

Color(s) - The colors do not correspond to the ones that the "Auto" &
"Apply" is supposed to set. I get sometimes black spheres although there
is no black color defined.

Size - Some spheres just dissapear. But I checked the values from the
column I use and I don't find that they so much different. And I though
that setting the "icon size" is some kind of scaling.

Is there anything special that I have to check? BTW, the documentation
of nviz looks outdated (?). Below some code.


# check range of srtm3
r.info srtm3_for_global_rad -r


# set region
g.region rast=srtm3_for_global_rad b=-10 t=2503 tbres=10 res3=0:00:03

projection: 3 (Latitude-Longitude)
zone:       0
datum:      wgs84
ellipsoid:  wgs84
north:      39:05:38.098741N
south:      38:23:35.098741N
west:       21:21:01.344612E
east:       22:26:13.344612E
top:        2510.00000000
bottom:     -10.00000000
nsres:      0:00:03
nsres3:     0:00:03
ewres:      0:00:03
ewres3:     0:00:03
tbres:      10
rows:       841
rows3:      841
cols:       1304
cols3:      1304
depths:     252
cells:      1096664
3dcells:    276359328

  ## even if working in WGS84, is the top, bottom to be defined
(always?) in metres?

  ## does, and how, the top-bottom and res3 resolution definitions
affect nviz?

# converting 2D points to 3D:
v.drape input="precipitation" rast="srtm3_for_global_rad"
output="precipitation_3d" method="bilinear"

# check for 3D-ness
v.info precipitation_3d | grep 3D

| Map is 3D: Yes |

# launch nviz
nviz elev=srtm3_for_global_rad points=precipitation_3d

  ## first image looks ok. Now working on colors/sizes is a mess :-?

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