Tim,
I got a bit swamped into the polygonize thing, which is at the heart of
what the GRASS people suggested to me. There's now a polygonize method
in GDAL too (thanks to Frank), with which one can create those
pixel-edged polygons of reclassed rasters. I haven't yet looked into the
smoothing much yet but GRASS seems to have some kind of simple smoothing
built-in into its polygonize method. GEOS has smoothing and simplifying
methods, even such that keep topology correct, but I don't believe they
would be easy to use for the complex polygons one gets from the polygonize.
There are some bugs in my contour -> polygon Perl code and it produces
overlapping polygons so it's far from perfect, but may produce nicer
results.
Ari
Tim Michelsen kirjoitti:
Hello!
Although your message is already some days old I wanna respond.
Did you ever want gdal_contour to produce polygons instead of lines?
Yes!
I made a small Perl program that uses the Perl bindings to GDAL and
which converts the lines into polygons. The polygons represent
"plates" of equal elevation and thus overlap. The polygons are stored
into a new layer in such an order that ordered rendering of them
produces a nice visualization. Visualization is my main goal here - I
want to get a similar effect as in some weather forecasts. However,
transparency does not work as expected in standard viewers because of
overlapping polygons. Here's an example created from DEM:
http://map.hut.fi/files/misc/contour_polygons.png
The code is also at http://map.hut.fi/files/misc/
I found this by googling:
http://lists.maptools.org/pipermail/fwtools/2005-November/000199.html
I wonder what's the current situation. Does GRASS do this?
It seems that GRASS cannot do this in a satisfying way. Or at least it
appears to be (don't wanna offend any GRASS dev/user).
Here I asked fro something similar:
http://thread.gmane.org/gmane.comp.gis.grass.user/24889
The maps I created with the suggested approach looked exactly as your
screenshots. The converted vectors didn't follow the countourlines
smouthly. Instead, the borders retraind the pixel-like raster outline.
Matplotlib and other plotting programs (matlab, IDL) can do this (see
the examples here: ).
So either
* plotting programs do an inaccurate interpolation
or
* the GRASS approach is too complicated that even experience users
don't find it.
Kind regards,
Timmie
--
Prof. Ari Jolma
Environmental Management Information Technology
Teknillinen Korkeakoulu / Helsinki University of Technology
tel: +358 9 4511 address: POBox 5300, 02015 TKK, Finland
Email: ari.jolma at tkk.fi URL: http://geoinformatics.tkk.fi
_______________________________________________
gdal-dev mailing list
[email protected]
http://lists.osgeo.org/mailman/listinfo/gdal-dev
