[GRASSLIST:5626] Re: Creating DTM from shapefiles

[Maciek Sieczka]

From: "Maris Nartiss" <maris.nartiss at gmail.com>
> Hi,
>
> I'm beginner with Grass and I have beginners problems :)
>
> I have 2 shape files one with lines and second with points. Both of
> them have HEIGHT parameter in attribute tables (lines - int, points -
> float (double precision)). To do some modeling, I need to create
> surface from those files.
> I read some docs and understood, that best surface creation algorithm
> in Grass it RST.
> Now I have Q - how to combine both source vector data layers to feed
> them to v.surf.rst?
> I was trying 2 solutions, but, due to lack of knowledge, both of them
> where dead ends.
> 1) Using v.patch to combine both vector data sources

v.patch in 5.7/6.0 is not operational yet. You'll find some workarounds in 
recent archives of grass5 list. You can also try patching two such vector 
layers (points and lines) with v.patch in Grass 5.4/5.5. It should preserve 
labels of both input layers properly. But always check whether the labels 
were really preserved as they should. It happened to me with one particular 
dataset that they were not for some reason (though maybe it was the dataset 
fault). If all is ok then import into 6.0 with v.convert.

> 2) Convert lines to points and then combine them with v.patch
> both worked fine but when I used d.what.vect I got only "Database
> connection not defined".

v.patch doesn't output any database - so there is nothing to be connected. 
Moreover the vector layer resulting from v.patch in 5.7/6.0 has all the cats 
of the input layers preserved, so you result in having lots of features with 
the same cat, thus it is not virtually possible to prepare an appropriate 
database manually. All you get in an output of that v.patch is a vectorial 
drawing actually.

> Any ideas, links to howtos etc. welcome.
>
> Maybe as a newbie with some ArcView background I'm unable to
> understand some Grass specific things, who cause my problems, but
> currently Grass docs aren't very helpful, mainly cuz they a bit
> outdated :(

v.patch manual should contain some remarks on these issues until it's fixed 
IMHO.

> TNX for reading this,
> Maris.

Cheers
Maciek