Using Math::Polygon to determine if point is inside a polygon. Not working

0
votes

I am trying to determine if a certain point is inside of a polygon. Trying to use Math::Polygon. I have the boundary of the polygon in a mySQL table as one record per point for the polygon: example:
1,38.33208,-75.51919
2,38.33286,-75.52265
etc.
38,38.33208,-75.51919

No matter what I do, the routine will not show the point inside the polygon despite the fact that the point would be truly inside the polygon.

Here's the relevant code

use Math::Polygon;

my @poly = ();
$sqlc = "SELECT segment,lat,lon FROM boundary WHERE xxxxxxx ";
my $stcc = $dbh->prepare(qq{$sqlc});
$stcc->execute();
while(($seg,$slat,$slon) = $stcc->fetchrow_array())
{
    $poly[$seg] = ([$slat,$slon]);
}
my $bound = Math::Polygon->new(points => @poly);
my @this_loc = ([$lat2,$lon2]);

if($bound->contains( $this_loc ))
{
    # never reaches this point. 
}

No matter what, I can't get the ->contains() routine to ever return true.

Any thoughts would be appreciated. Thanks.

1
perlpolygoncpan
Are you using use strict; use warnings;? If not, you should. - melpomene

1 Answers

1
votes

There seems to be (at least) two errors:

my $bound = Math::Polygon->new(points => @poly);

the constructor takes a reference to an array, not an array. So it should be:

my $bound = Math::Polygon->new(points => \@poly);

Second, $bound->contains( ) takes a reference to a point array, so it should be:

if($bound->contains( \@this_loc )) { ... }