Paul,
Paul Meems wrote:
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?
If you do not provide a GeoTransform to the png file then it is "upside
down" as the default coefficient for y_line is 1 and not -1. It can be
set from a world file as explained here:
http://www.gdal.org/frmt_various.html
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?
Maybe the png file contains many 8-connected features? Polygonize uses
4-connectness. Polygonize method doesn't seem to have connectedness
parameter, which is a pity IMHO(*).
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.
I'm not aware of vectorize method in GDAL, which produces polylines.
Best regards,
Ari
(*) maybe we could use the Options list for that?
Thanks in advanced for any advice.
Paul
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