OpenEuphoria

Re: finding if point is inside irregular rectangle

• Posted by cetaylor at compuserve.com Feb 25, 2002
• 427 views

This is one way of doing it:

1. imagine a horizontal line through the Point
2. compute the x-value where any polygon side crosses the imaginary line
(simple geometry using the slope of the side)
3. if the x-coordinate of the Point is greater than an odd number of
x-values then the Point is inside the polygon.  If it is less than the
lowest x-value or greater than an even number of x-values, then it is
outside the polygon

Colin Taylor

----- Original Message -----
From: "Al Gonzalez" <alg at nomscon.com>
To: "EUforum" <EUforum at topica.com>
Sent: Monday, February 25, 2002 4:52 PM
Subject: RE: finding if point is inside irregular rectangle


>
> "far from trivial" maybe an understatement unless you are up on all of
> your geometry.
>
> Have a look here:
> http://www.acm.org/tog/resources/RTNews/html/rtnv5n3.html#art3
>
> There is some discussion and sample code in C
>
> gwalters at sc.rr.com wrote:
> > then it's a polygon...and it's far from trivial to find if a point is
> > inside.
> >
> > george
> > ----- Original Message -----
> > From: <tone.skoda at siol.net>
> > To: "EUforum" <EUforum at topica.com>
> > Sent: Monday, February 25, 2002 4:05 PM
> > Subject: Re: finding if point is inside irregular rectangle
> >
> >
> > > No I don't mean that. It can have angles which are not 90 degree.
> > >
> > > ----- Original Message -----
> > > From: <bensler at mail.com>
> > > To: "EUforum" <EUforum at topica.com>
> > > Sent: Monday, February 25, 2002 9:57 PM
> > > Subject: RE: finding if point is inside irregular rectangle
> > >
> > >
> > > > He means a rectangle that is not exactly horizontal and vertical.
It's
> > > > still a rectangle, but on an angle, like a diamond with 90 degree
> > > > corners.
> > > >
> > > > Chris
> > > >
> > > > Brian Broker wrote:
> > > > > Hate to be a stickler here but "irregular rectangle" sounds like
an
> > > > > oxymoron.  A rectangle is a four-sided polygon having all right
> > angles.
> > > > >
> > > > > Perhaps you mean "irregular quadrilateral"...
> > > > >
> > > > > -- BB
> > > > >
> > > > >
> > > > > tone.skoda at siol.net wrote:
> > > > > > Here's another problem: I need to find out if point lies inside
> > > > > > an irregular rectangle. Irregular rectangle has
> > > > > > 4 corners but they don't need to be 90 degree, although they can
> > still
> > > > > > be.
> > > > > >
> > > > > > Example of irregular rectangle:
> > > > >
> > > > >