<blatant lie>Yeah, me too. I was just about to do that! </blatant lie> Fantastic!
----- Original Message ----- From: "Graham Jones" To: TimSC Cc: talk-gb@openstreetmap.org Subject: Re: [Talk-GB] building shapes from OS Street View Date: Fri, 9 Apr 2010 22:32:40 +0100 Hi Tim,That is exactly the sort of thing I had envisaged writing - you have nearly finished before I got started - well done! Graham. On 9 April 2010 22:25, TimSC <mapp...@sheerman-chase.org.uk> wrote: Hi again, I have been working on auto tracing buildings and I'm making progress. I was slightly encouraged by Ed Avis's comments. I think one underlying difference is peoples attitude to omissions in map data. Many people think they are a good thing, particularly since they encourage the community to do high quality surveying. But I think omissions are bad in terms of actually using the map. I don't think we should be using the main map to gauge our progress. I suspect what we need is good meta data - how and when data is sourced. Anyway enough rambling... Tracing buildings. I have been using the original images, since image transformations tend to introduce degradation of quality. I use colour to select building pixels, then form edge fragments, then form polygons, then simplify the polygons using the Douglas-Peucker algorithm, then group them so we get inner and outer edges, then tranform image coordinates to GBOS then to WGS84 via OSTN02 (I ported the perl code to python), then save as OSM format and load back into JOSM. Screenshot: http://timsc.dev.openstreetmap.org/dev/josm-building-outlines.png The next steps are to improve the quality of the polygon shapes, possibly by checking if the edges are nearly orthogonal, and if so making them completely orthogonal. Also I need to write a filter to check for buildings in the area, to avoid importing duplicate buildings. I need to look at the simplification, as sometimes an extra node is added to a polygon (the initial node used as the start of the algorithm). I am also considering detecting roads that overlap buildings in the source images, since this is probably the biggest loss of quality. The result I am getting is already more spatially detailed than my own survey of the University of Surrey campus (although not as rich in information). In the medium term, I will import some buildings once I have the quality I want. I want to minimise manual work in JOSM but I don't rule it out. I will only be working in the Guildford area - it's my data to gamble around there :) TimSC _______________________________________________ Talk-GB mailing list Talk-GB@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-gb -- Dr. Graham Jones Hartlepool, UK email: grahamjones...@gmail.com _______________________________________________ Talk-GB mailing list Talk-GB@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-gb -- _______________________________________________ Surf the Web in a faster, safer and easier way: Download Opera 9 at http://www.opera.com Powered by Outblaze
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