Hi all GRASS users,
I have used r.surf.contour for the first time to create a raster elevation
map from a rasterized contour map. The original map had only 30 lines and
the surface it was quite small (about 50 hectars). To calculate the raster
map which is made of 780 cols by 530 rows my computer worked more than 4.30
hours. Something wrong ? Is there exist a more quick way to obtain the same
result? If not, how many times I need in case of 500 or more hectars with
same resolution?
Is my computer too old for these jobs ?
I used a Pentium 166 with 64MB of RAM, with linux RH 6.2, and GRASS 5beta6
version.
Thanks in advance
Stefano
*************************************
Stefano De Felici
Via Gioberti, 32
I - 00044 Frascati
(Roma)
ITALY
E-mail s.defelici@tin.it
s.defelici@tiscalinet.it
tel./fax ++39 - 069419651
Hello Stefano
I don't know if this will help you or not but the following comes from
the man page for r.surf.contour. It notes the conditions that are
required for r.surf.contour to run well.
===================================================================
r.surf.contour works well under the following circumstances: 1) the
contour lines extend to the the edge of the current region, 2) the
program is run at the same resolution as that of the input map, 3) there
are no disjointed contour lines, and 4) no spot elevation data BETWEEN
contour lines exist. Spot elevations at the tops of hills and the
bottoms of depressions, on the other hand, improve the output greatly.
Violating these constraints will cause non-intuitive anomalies to appear
in the output map. Run r.slope.aspect on r.surf.contour results to
locate potential anomalies.
The running of r.surf.contour is very sensitive to the resolution of
rasterized vector map. If multiple contour lines go through the same
raster, slight anomalies may occur. The speed of r.surf.contour is
dependent on how far "apart" the contour lines are from each other (as
measured in rasters). Since a flood fill algorithm is used, the
program's running time will grow exponentially with the distance between
contour lines.
===================================================================
This will only help if your data does not conform to one or more of
these conditions.
I hope this at least gave you some ideas.
--
Sincerely,
Jazzman (a.k.a. Justin Hickey) e-mail: jhickey@hpcc.nectec.or.th
High Performance Computing Center
National Electronics and Computer Technology Center (NECTEC)
Bangkok, Thailand
People who think they know everything are very irritating to those
of us who do. ---Anonymous
Jazz and Trek Rule!!!
Oops! Most of those conditions are for accuracy not speed. The distance
between contour lines is a factor though.
--
Sincerely,
Jazzman (a.k.a. Justin Hickey) e-mail: jhickey@hpcc.nectec.or.th
High Performance Computing Center
National Electronics and Computer Technology Center (NECTEC)
Bangkok, Thailand
People who think they know everything are very irritating to those
of us who do. ---Anonymous
Jazz and Trek Rule!!!
Hello Stefano,
just a hint: The current GRASS 5 version in CVS (not yet
released in a package) contains an updated version of
v.surf.rst
which can be used to interpolate raster surfaces from contours
using a Spline algorithm. The results will be better than from
r.surf.contour (probably it's not faster...).
Kind regards
Markus Neteler
Hi, grass users...
I'm a new grass user and I'm also going to start the work at Perugia
University as PhD student....
My professor ask me to study Debris Flow, but instead I'm really interested
about gis and particulary about Grass....
Do you know some experiences about the use of grass concerning debris flow, or
landslide???
Best Regards...
Ivan
--
*************************************************
Ivan Marchesini
PhD Student in Applied Geology, Hydrogeology, Geomorphology
Civil and Environmental Engineering
Perugia University
Via G. Duranti, 6/A
06125 PERUGIA
Italy
Tel: 075/5853760
Cell: 0349/6419338
E-Mail: marchesini@unipg.it
ivanm@mailroom.com
ivan@flintstones.sct.unipg.it
*************************************************