[GRASS-user] dems from coordinate lists

[Hanlie Pretorius]

Hi Micha,

I tried your suggestion after setting the region to 20m instead of the
raster DEM's 25m.:

v.surf.rst input="dem_2628cc_25m at C83" layer=0
elev="dem_2628cc_rst_elev" tension=40. segmax=40 npmin=120
dmin=9.998022 dmax=49.990111 zm  ult=1.0

This worked, but the differences between the raster DEM that I created
with r.in.xyz and the rst interpolated results are quite big - ranging
from -6.882202m  to +7.864258m.

It also ran fairly slowly. Without adjusting the npmin paramter from
the default (300) to 120 it literally ran for hours (Win XP, 3GHz CPU,
1GB RAM). Adjusting npmin to 120 didn't seem to affect the error range
of the outcome much.

Is there a reason why I should use r.surf.rst instead of v.surf.rst?

Or perhaps I should just import the points with r.in.xyz and leave the
DEM in this format for further applications (hydrological modelling)?

Regards
Hanlie

2010/5/13, Micha Silver <micha at arava.co.il>:
> MS wrote:
>
>> If I follow correctly, instead of v.to.rast, you need to interpolate a
>> raster DEM from the points.   v.surf.rst produces nice results, but
>> there are other interpolation modules as well in the raster category.
>>
> That's the method I use also.
> I start with:
> v.in.ascii -z in=<ascii_file> z=3 out=vect_pts
> This creates a 3D vector using the z column as the height values.
> Now set the desired region:
> g.region vect=vect_pts res=xxx
> Choose the raster resolution that suits your needs. If the points in the
> ascii file are at 25 m spacing, then you probably could interpolate at
> 10m-20m resolution (or better) with no problems.
> Then:
> v.surf.rst in=vect_pts layer=0 elev=dem ...
> The layer=0 parameter indicates that you're using the 3D vector's z
> value for elevation.
> --
> Micha