PDL-2.4.10 and later include a pnpoly routine which may
be of use:
pdldoc pnpoly
Module PDL::Image2D
pnpoly
'points in a polygon' selection from a 2-D piddle
$mask = pnpoly($x, $y, $px, $py);
For a closed polygon determined by the sequence of points in {$py,$py}
the output of pnpoly is a mask corresponding to whether or not each
coordinate (x,y) in the set of test points, {$x,$y}, is in the interior
of the polygon. This is the 'points in a polygon' algorithm from
<http://www.ecse.rpi.edu/Homepages/wrf/Research/Short_Notes/pnpoly.html>
and vectorized for PDL by Karl Glazebrook.
# define a 3-sided polygon (a triangle)
$px = pdl( 3, 20, 34 );
$py = pdl( 3, 20, 3 );
$img = zeros(40, 40); # create test image
$x = $img->xvals; # get x pixel coords
$y = $img->yvals; # get y pixel coords
# $tri is 0 everywhere except for points in polygon interior
$tri = pnpoly($x,$y,$px,$py);
As for more, PDL has a lot of tools to make such
computations work (implementable and with good
performance). The PDL home page is a good place
to start for more information: http://pdl.perl.org
--Chris
On Wed, May 2, 2012 at 2:49 PM, Craig DeForest
<[email protected]> wrote:
> There is a very nice algorithm in Preparata and Shamos ("Computational
> Geometry"). I, for one, would love to have a PDL::PlanarGeometry package
> built, to treat 2xN PDLs as collections of points on the plane. Nice
> algorithms to start with would include:
>
> - area
> - hull
> - Voronoi
> - delaunay
> - polygon union
> - polygon intersection
> - polygon clean
>
>
>
> On May 2, 2012, at 12:33 PM, Steven Lembark wrote:
>
>>
>> The nice people at Oracle implement all of their OpenGIS
>> "contained within" geometry operators using bounding boxes
>> only. This makes it impossible to select non-rectangular
>> areas from a map.
>>
>> Google has gotten me nowhere looking for a PDL geometric
>> operator library that (ideally) works on OpenGIS format
>> data (WKB, WKT) or at least implements a "contains"
>> operator suitable for a point and polygon.
>>
>> I am not trying to plot anything, just get a boolean
>> outcome for, say, which state contains a given lat+long
>> or which hospital is closesest to a given point.
>>
>> Checking CPAN for PDL+GIS gives me PDL::GIS::Proj, which
>> isn't about GIS and is also pretty much dead.
>>
>> Q: Any suggestions for an implemention for selecting
>> which of a (largeish) list of polygons contain a
>> given point?
>>
>> thanks
>>
>> --
>> Steven Lembark 3646 Flora Pl
>> Workhorse Computing St Louis, MO 63110
>> [email protected] +1 888 359 3508
>>
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>>
>
>
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