[RNFdev] Not a pretty picture

[Frank Warmerdam]

Dan Putler wrote:
> Well, I've created a well behaved radial sort program in R. 
> Unfortunately, it doesn't completely solve the scrambled vertices 
> problem when the road segments are used as the basis of creating the FSA 
> polygons. Below is a screen shot of what I'm getting after the radial 
> sorting of the vertices, while the second one shows what I get without 
> sorting the vertices. Both of these are for FSA K2W. The last thing I 
> could do is take the convex hull of the vertices, but this would also 
> have problems as well. Based on this exercise, I don't know whether it 
> is practical to use the FSA boundary road segments directly in forming 
> FSA boundaries. Frank, any ideas other than using a radial sort or a 
> convex hull to get the vertices in the correct order?

Dan,

Is the problem that you are assembling a polygon from a set of linear
features (roads) without any direct information on how they should be
stitched together?  I have code for assembling polygons from a set of
linestrings but it depends on the end of line line string matching only
one other line string end.

But I got the impression you are starting with a randomly ordered set of
points that define the polygon border.  If this is the case, it seems you
don't have enough information to create the polygon in cases less than
perfectly conditioned situations.

If you can provide some input data in a reasonable accessable format, I
could look at whether it is easily assembled.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | President OSGeo, http://osgeo.org