[GRASS-user] topo map to dem

[antonio rodriguez]

Hamish escribió:
> antonio rodriguez wrote:
>   
>> I apologize if this question has been posted before, but I couldn't
>> find something searching through the mailing list.
>>     
>
> it helps if you know the secret words, try searching for "r.thin".
>
>
>   
>> Is it posible to perform the task of extracting a DEM from a scanned 
>> topographic map in GRASS? I mean like Autodem or R2V programs.
>>     
>
> using r.resample or r.mapcalc, or maybe with "select by color" in a
> graphics program, select only the lines you are interested in, make
> every thing else white/NULL. You might have to use v.mkgrid + v.buffer
> to get rid of any lat/lon grid lines the same color as isolines.
>
> Once you only have raster versions of the isolines, run r.thin to get
> rid of noise, then run "r.to.vect feature=line".
>
> then add an elevation column to the vector map (v.db.addcol), v.digit or
> QGIS to clean out junk, and "d.what.vect -e" to label lines with
> elevation values.
>
> Finally use v.surf.* or r.surf.contour to convert into a DEM.
>
>
> I've done this with bathymetry charts and it takes some manual labor but
> works pretty well.
>
>
> Hamish
>
>   
Thanks for the advice! I will try to do it this way

Cheers,

Antonio