On Friday, August 26, 2011, Stan West <stan.w...@nrl.navy.mil> wrote:
> From: Benjamin Root [mailto:ben.r...@ou.edu]
> Sent: Friday, August 19, 2011 13:43
>
> I have an arbitrary list of coordinates that I know represent the boundary
of a polygon. Is there some sort of function from the contouring or path
codes that would allow me to pass in that list and get back the resorted
list with the path codes with it?
>
> Hi, Ben. Is it the order of the points around the polygon that is unknown,
and is it unambiguous because the polygon is known to be convex? If so, I
believe you could use part of the Graham scan [1] convex hull algorithm. The
function you need would find the point P with the lowest Y coordinate, then
sort the remaining points by the cosine of the angle they and P make with
the X axis. After that, the list comprising P and the sorted points would
need the path codes.
>
> If the polygon is concave but the order is somehow clear (e.g., a radial
progression about the average coordinate), you might be able to adapt the
method. I hope I understood your problem correctly and that this helps.
>
> [1] http://en.wikipedia.org/wiki/Graham_scan
Actually, that might be useful. The current solution I have is to use the
core contouring function in mpl to generate paths, but they doesn't seem to
guarantee either clockwise or counter-clockwise traversals.
Does graham scan guarantee something like that? I need to calculate
outward-facing normal vectors.
Ben Root
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