OpenEuphoria

Re: finding if point is inside irregular rectangle

• Posted by Derek Parnell <ddparnell at bigpond.com> Feb 25, 2002
• 429 views

Not sure if this works for concave polygons.

26/02/2002 10:37:49 PM, cetaylor at compuserve.com wrote:

>
>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:
>> > > > >
>> > > > >
>
>
>
---------
Cheers,
Derek Parnell