User talk:TomChance/VectorisingStreetView

From OpenStreetMap Wiki
Jump to: navigation, search

how do the borders of "important" buildings affect their size? Ojw 12:48, 28 June 2010 (UTC)

I'm not sure whether the red/brown borders should be considered part of the building. However, the StreetView buildings aren't particularly accurate, and the steps I have taken aren't a particularly accurate vector trace of the StreetView raster images. So I wouldn't think that the borders add any significant extra margin of error. Given the inaccuracy of StreetView I think it is only useful to get a rough approximation of buildings into OSM that can be tidied up later on with ground surveys and high quality aerial photography. TomChance 13:03, 28 June 2010 (UTC)

Potrace comments

I'm the author of Potrace, and I have a few comments on the article. This is a really cool application of Potrace!

  • Starting from version 1.10, Potrace has a DXF backend, so you can probably skip the part where you use pstoedit to convert from EPS to DXF.
  • You can tell Potrace to produce a polygon, rather than Bezier curves, by setting the alphamax parameter negative (options -a -1).
  • Probably the reason the file was smaller than you expected was that the default behavior of the EPS backend (until version 1.9) was to shrink the image to fit on a letter-sized page for printing. That behavior changed in 1.10; the new default is to scale to 72dpi. In either case, the -r option can and should be used to set a fixed resolution if you need input and output coordinates to be related in some fixed way.