[gdal-dev] Re: Countour polygons instead of lines
timmichelsen at gmx-topmail.de
Tue Sep 9 16:37:19 EDT 2008
Although your message is already some days old I wanna respond.
> Did you ever want gdal_contour to produce polygons instead of lines?
> 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:
> The code is also at http://map.hut.fi/files/misc/
> I found this by googling:
> 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:
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: ).
* plotting programs do an inaccurate interpolation
* the GRASS approach is too complicated that even experience users don't
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