[GRASS-user] topo map to dem

GRASS GRASS user
1

Hi,

I apologize if this question has been posted before, but I couldn't find something searching through the mailing list.

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.

TIA

Antonio

2

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

3

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