[GRASS-user] Making fake dem's

GRASS GRASS user
1

Hello Markus and Wolfgang,

Thanks for your responses.

why not takeing real DEMs? The SRTM dataset is for free and can be used
with grass.

Because I want to make specific landscape shapes. It would be an
immense labour to search the archive of DEM's to find what I want.

take a look at r.surf.fractal which is creating synthetic DEMs
for you.

I have GRASS installed on two machines. r.surf.fractal worked fine on
my machine at home (6.2.1) but does not exist on my work machine (also
6.2.1). In both cases GRASS was installed from source. Can you tell
me what libraries r.surf.fractal depends on so I can figure out how to
re-configure and re-build?

Thanks,

Roger

2

Roger Mason wrote:

> why not takeing real DEMs? The SRTM dataset is for free and can be
> used with grass.

Because I want to make specific landscape shapes. It would be an
immense labour to search the archive of DEM's to find what I want.

Another idea is to use r.mapcalc to make a gaussian bell etc.

> take a look at r.surf.fractal which is creating synthetic DEMs
> for you.

I have GRASS installed on two machines. r.surf.fractal worked fine on
my machine at home (6.2.1) but does not exist on my work machine (also
6.2.1). In both cases GRASS was installed from source. Can you tell
me what libraries r.surf.fractal depends on so I can figure out how to
re-configure and re-build?

GRASS needs to be built with FFTW support for r.surf.fractal to work.
Note about that just added to the help page.

dev:
I notice frac.h still defines prototypes for some fns which are now taken
from the fftw lib, and does not #include any fftw headers, or even
<grass/gmath.h>. ??

CVS log of switch to FFTW:
http://freegis.org/cgi-bin/viewcvs.cgi/grass/src/raster/r.surf.fractal/Attic/fft.c

Hamish

3

Hamish wrote on 07/04/2007 08:04 AM:

Roger Mason wrote:

why not takeing real DEMs? The SRTM dataset is for free and can be
used with grass.
      

Because I want to make specific landscape shapes. It would be an
immense labour to search the archive of DEM's to find what I want.
    
Another idea is to use r.mapcalc to make a gaussian bell etc.
  

See testsuite/raster/rhemisphere.sh for example in the source code.

Markus

------------------
ITC -> dall'1 marzo 2007 Fondazione Bruno Kessler
ITC -> since 1 March 2007 Fondazione Bruno Kessler
------------------

4

Hello Hamish,

Hamish <hamish_nospam@yahoo.com> writes:

Roger Mason wrote:

> why not takeing real DEMs? The SRTM dataset is for free and can be
> used with grass.

Because I want to make specific landscape shapes. It would be an
immense labour to search the archive of DEM's to find what I want.

Another idea is to use r.mapcalc to make a gaussian bell etc.

Thank you, I'll give that a try.

> take a look at r.surf.fractal which is creating synthetic DEMs
> for you.

I have GRASS installed on two machines. r.surf.fractal worked fine on
my machine at home (6.2.1) but does not exist on my work machine (also
6.2.1). In both cases GRASS was installed from source. Can you tell
me what libraries r.surf.fractal depends on so I can figure out how to
re-configure and re-build?

GRASS needs to be built with FFTW support for r.surf.fractal to work.
Note about that just added to the help page.

Yes, after poking around I guessed that might be the case and rebuilt
with fftw support but have not tested yet. Thanks for confirming my suspicions.

Many thanks for your help.

Roger