Smathermather's Weblog

Remote Sensing, GIS, Ecology, and Oddball Techniques

What is the center line of a complex polygon? (cont.)

Posted by smathermather on September 26, 2011

If we try to extract the centerline of a polygon using Voronoi polygons, like in my previous post, it works pretty well for hydrologic cases, like extracting a stream centerline from stream banks, e.g.:

Stream/River with digitized banks

Stream/River centerline extracted from stream banks

We’ll use this to extract flow lines, in order to build out a better hydrologic network, but also use it to update property boundaries based on deed descriptions which may alternately follow distances and bearings, or banks and centerlines of streams and rivers.

But, I was still curious to see how well it does on smaller polygons, e.g. does it help with labeling of parcel polygons:

Not perfect, but not bad.   Looks like developing a special case for equilateral triangle, circular, and square shaped polygons (etc) might be in order, as these are probably best labeled in a more simple fashion (see northeast corner of this map, parcel 48517140)… .

2 Responses to “What is the center line of a complex polygon? (cont.)”

  1. The Geotools/GeoiServer built-in labelleler has an option to use the “minimum bounding rectangle”, might give good results for parcels:
    mbr

    http://docs.geoserver.org/latest/en/user/styling/sld-reference/labeling.html#polygon-alignment

  2. Admittedly, the fit from mbr would probably give a better result in this case, since the polygons are not long– that “forking” effect of the Voronoi polygons really gets in the way for this size. It works really nicely for the long, skinny, curvy ones though… .

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