Micha Silver wrote:
On 07/12/2012 05:23 PM, David M. Lawrence wrote:
Dear all:
I tried all of this -- contour does work on my machine with a dataset
I downloaded from an online tutorial, so I think the problem may be
with my data instead. The tutorial's data were obtained from an
evenly spaced grid.
My data are not evenly spaced. They are soundings (depth
measurements) from a quarry linked to geographic data obtained via a
GPS receiver. The measurements are irregularly spaced.
In that case I'd definitely suggest you first create an interpolated
raster (DEM) from the points. Then use that raster to extract contour
lines. GRASS is one possible tool for this. The relevant modules would
be:
v.in.ascii (to get your points into a GRASS point vector)
g.region (to set the region to the area covered by the points, and
choose a suitable resolution)
v.surf.rst (to interpolate the points and create a DEM raster)
r.contour (to delineate vector contour lines from the DEM )
v.out.ogr (if you need to export the GRASS contour vector to other
formats)
WIth only 900 points the above should be no more than a few minutes...
I've had trouble using grass (my fault not grass's:) but once you have
your vector layer in qgis you can also use the Raster/Analysis/Grid tool
to create the raster (this uses the gdal tool gdal_grid) and then use
the Raster/Extraction/Contour (again this uses another gdal tool). I've
had pretty good luck with this method. You probably have to save your
vector data as a shapefile first but gdal also has direct support for
csv so maybe not.
HTH,
Micha
The latest version of the data set has more than 900 points covering
75 percent of the aerial extent of a quarry. I've been running the
contour procedure for 12 hours now. The contour dialog box indicates
it is "not responding," but I know from other software that that may
mean the contour procedure is actually thinking.
Every time I check Task Manager (I'm running QGIS Wroclaw on Windows
7-64) the number of processes seems to fluctuate around 50, with an
observed range of 42 to 52. The amount of memory consumed ranges
from 68,000 Kb to a little more than 100,000 Kb.
From this, I consider the hypothesis that contour is working more
likely than the hypothesis that it has frozen. Comments, anyone?
Thanks again for your time.
Sincerely,
Dave Lawrence
On 7/10/2012 3:58 AM, Alister Hood wrote:
Anyway, since you seem to be able to start the plugin, your problem
doesn't appear to be with getting it all installed. Some ideas:
- Try the plugin on an even smaller dataset to see if it works (If
I remember correctly, I think it might be quite slow, but several
hours for 400 points does seem like a very long time).
- When the plugin appears to be frozen, can you look in the windows
process manager to see if it is actually doing any work?
- Remove the separate Python and all the associated junk to see if
that is affecting QGIS. (But I doubt that it is)
- Provide your data for someone else to check that it works fine on
their system.
Also, I could be wrong, but I think I remember this plugin freezing
for me, and then somehow working fine when I tried it again with
exactly the same options... have you tried it a second time?
Regards,
Alister
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