Smathermather's Weblog

Remote Sensing, GIS, Ecology, and Oddball Techniques

What is the center line of a complex polygon? New approach.

Posted by smathermather on January 17, 2012

Today, I just show pictures of my process for filtering the medial axis of extraneous elements. I’ll let the pics tell the story for now:

Original Geometry, with ST_Segmentize run to densify the vertices

Medial Axis (Calculated outside PostGIS... at this time)

Density of vertex points in Medial Axis-- proportional to how closely it matches the direction of the local geometry

Medial Axis filtered based on density of vertices. Red segments are the removed ones, blue are the retained. It's not perfect, but it's very cheap computationally... .

scale axis transform 3

scale axis transform 2
scale axis transform 1

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3 Responses to “What is the center line of a complex polygon? New approach.”

  1. Nathan Hopper said

    I found your post today and I’m very interested in your techniques. I’m conducting some research on river depth probabilities from belief networks but one of my main inputs is the centerline of the river polygon. I already have geoprocessing tools to derive the river polygon quickly but now I need a way to derive the centerline. I found some GP tools but they require ArcInfo and I only have acess to Editor. I’m not that familiar with other GIS softwares do most of my work through the geoprocessor or python. Any help or suggestions would be greatly appreciated.

    Thanks,
    Nate

  2. […] had a series of posts (including this one) on finding the center line of a complex polygon– especially with an interest in finding the […]

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