[gdal-dev] Re: Open source API to convert raster to polygons?

Brent Fraser bfraser at geoanalytic.com
Fri Jun 6 11:07:39 EDT 2008


  I couldn't get Autotrace to give me what I wanted.  In the end I wrote some code using GDAL and OGR for the raster and vector I/O.

  Most raster-to-vector problems are far more difficult than mine; in those cases, the need is to re-constitute a scanned map (or drawing) to it's original "vector" format.  For my simple problem, I just needed to connect adjacent pixels with line segments.


Klokan Petr Přidal wrote:
> Hi Brent,
> have you tried "autotrace"? It has the centerline functionality and
> several parameters to tweek the result.
> To a shapefile you will have to go trough DXF, probably. And you need
> to correctly handle conversion from raster coordinates to a map one.
> http://autotrace.sourceforge.net/
> Autotrace is open-source, are the algorithms interesting (and useful)
> for GIS tools as well?
> Another program, which came to my mind is "potrace". There is a list
> of "Similar Projects:" on the autotrace website.
> Can you later on post a note about the toolchain you have choosen?
> Klokan
> On Wed, Jun 4, 2008 at 11:17 PM, Brent Fraser <bfraser at geoanalytic.com> wrote:
>> Dan (and others),
>> I've compiled your gdal_trace_outline code on Windows XP / VS2003.NET with
>> only a few minor problems (I can send details if you are interested).
>> Unfortunately I've got a bunch (56) 1-bit tiff files generated from an image
>> segmentation process I want lines (ok, polygons) for.  So I really want to
>> vectorize the centerline of the pixels, not their outlines.  How hard would
>> it be to modify gdal_trace_outline to do this?
>> To others interested:          I've experimented with ras2vec
>> (http://www.xmailserver.org/davide.html) and had some success, but it misses
>> generating a few line segments where the "edge" pixels are adjacent. I've
>> been able to use OpenJump to polygonize the lines (after bumping up the
>> allocated memory on startup), so that part is ok.
>>        I plan on looking into Grass too...
>> Thanks!
>> Brent Fraser
>> GeoAnalytic Inc.

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