[gdal-dev] [GDAL 1.7] GDAL_Contour png file

Paul Meems bontepaarden at gmail.com
Mon Jun 7 07:49:18 EDT 2010

Hi List,

I'm trying to vectorize a png file to a shapefile.
This png file only contains lines with one color.
Using this command a nice shapefile is generated:
gdal_contour -a elev test.png contour.shp -i 10.0 -snodata 255

But the shapefile is the wrong size up.
Up and bottom are flipped.
How do I fix that?

The generated shapefile is huge: 97MB from a 205 kB png file (high
resolution: 6720 x 4984  Pixels)
The shapes created are all very small/short and should be chained together.
Can GDAL do that as well?

I tried gdal_polygonize.py already and that is looking better, but because
not all lines are correctly closed not all polygons are good.
I'm looking for something similar, but the output should be polylines
instead of polygons.

Thanks in advanced for any advice.

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