[HOT] Advice tracing footprints with poor imagery in Kathmandu, Nepal

Paul Norman penorman at mac.com
Fri Feb 8 07:38:56 GMT 2013


> From: maning sambale [mailto:emmanuel.sambale at gmail.com]
> Subject: Re: [HOT] Advice tracing footprints with poor imagery in
> Kathmandu, Nepal
> 
> There are opensource tools that can extract features from hires imagery,
> an example is GRASS, see this sample process (ignore the subjectline :))
> 
> http://lists.osgeo.org/pipermail/grass-user/2007-August/040808.html
> 
> But this requires, that you have direct access to the imagery (which
> isn't legally allowed with Bing)
> 
> Another option for small areas is to try balloon/kite mapping:
> 
> http://grassrootsmapping.org/
> 
> In my experience, the most effective way is by manually tracing in JOSM
> (no computer algorithm can do what a human can see, at least not
> yet) and of course ground validation.

The last time someone proposed importing automatically generated building
outlines[1] the consensus was against it. They used multispectral imagery
and LIDAR coverage and there were still significant concerns about the
quality. One of the basic problems with automatic building detection is that
buildings tend to consist of right angles but automatic detection methods
tend be better with irregularly shaped areas like tree coverage. I imagine
any proposed import would run into similar issues, particularly since the
imagery in Nepal is likely not as good as the multispectral+lidar that
vtcraghead had.

[1]: http://lists.openstreetmap.org/pipermail/imports/2012-March/001267.html




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