[Talk-us] UVM-SAL Buildings
penorman at mac.com
Fri Jun 1 03:39:28 BST 2012
I have a few specific comments, and some more general ones
> From: William Morris [mailto:wboykinm at geosprocket.com]
> Subject: [Talk-us] UVM-SAL Buildings
> Howdy Folks,
> Trying this again, after a hiatus, here is a sample of a few hundred
> buildings from a UVM-SAL land use classification. In this case it's for
> an area just west of D.C. in Montgomery County, MD. I offer it for your
> consideration before I pull the import trigger:
Before importing, don't forget to follow the other steps in the import
guidelines about documenting it on the wiki.
> Some steps I've taken to make it community-friendly include:
> - Removed all buildings that intersected existing OSM features
> - Removed all buildings smaller than 5000 square meters in area, since
> those residential structures weren't being very well-detected anyway
> - I hopehopehopehope the footprints survived their trip from QGIS
> through ogr2osm to JOSM (If there's anything wrong with the tags please
> let me know so I can solidify the process)
> Thanks again to Andrew Guertin for adapting ogr2osm so perfectly.
> Python has never been so easy.
I noticed the following issues:
The AREA and PERIMETER tags are superfluous - the area and perimeter can be
trivially computed from the geodata.
The LandCover tag also doesn't seem to serve any purpose as it only ever has
There are building=yes tags on ways in multipolygons - these should be on
the MP, not on the ways. Did you run it through ogr2osm and then select
type:way in JOSM by any chance? It would be better to write a translation
file to apply the appropriate tags to the appropriate objects. If you did
this, try my version of ogr2osm at https://github.com/pnorman/ogr2osm and
let me know if the problem still occurs, since then it would be a bug.
The detection seems pretty good. I was only able to find one false-positive
and a couple places where buildings had merged together, as well as a couple
of places where one building ended up split.
Some of the ways seem a bit over-noded. Normally I'd suggest JOSM's simplify
way tool but I'm guessing there might be a more effective point in the
workflow to do this.
Buildings tend to be rectangular and have a lot of straight lines so it's
really noticeable where these don't. Errors which would not be particularly
noticeable on a forest or a lake become more so on buildings. I'm hesitant
to suggest a fix for this.
I'm also not sure about the usefulness of the data. If a user later comes
along and wants to improve it, it'd be faster to delete and recreate it than
to improve the ways.
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