[GRASSLIST:9494] Re: dem from vector files...help...

[Hamish]

> I'm harris, i'm a student and I'm a new user of Grassgis 6.0. I
> started using Grass because of an essay and i have to finish it to get
> my degree...So i have to make a digital elevation model from some
> vector files.The vectors are containing elevation info and was
> digitized to arcmap.So i followed the following method : I imported
> the ersi .shp,I had 4  shp files so i made  4 vector files.Then I 
> combined the 4 vector files to make them one. i used the v.patch
> command. Then i think that i used v.clean to snap the common vector
> lines but i not so sure if that was neccessary.was it? what other
> steps i must do? Then i tried to connect from another esri shp (that
> was containing all the vectors together from the begging) the dbf .i
> managed to connect the tables. My next step was to make vector to
> raster so i used v.to.rast. an my command was
>  v.to.rast input=string [layer=1] output=string [use=att]
>  [column=elevation (the column that contains elevation info iin my
> case.) is this correct? When i did that i finally used v.surf.contour
> to make my dem. So i'm waiting for hours for my dem to be done but
> it's procceding very slowly.
> Is that the right way to combine vectors?Cause the first time i tried
> to make my dem throught that way i got a very bad dem...V.patch
> combines the dbf of each vector?i think that it isn't. 
> 
> That's all, i not so sure if i did the right steps in general and
> that's why i need your help anyway.If anyone could help me id be very
> grateful.


That all seems ok. (except the module is called r.surf.contour)

One change I might make: don't bother with v.patch, just do v.to.rast on
the four component vectors and then use r.patch to combine the parts.

r.surf.contour will take a long time if there are large gaps without
contours (e.g. a flood plain) as for each cell it has to look a long way
for data. Rather inefficient algorithm, maybe r.cost's approach could help?
Let it run over night. It will get there in the end.



Hamish