RE: [Mesa3d-dev] Seriously off-topic question...

[<her...@ru...>]

Thank everyone for the quick answers... they helped a lot!

- Heriberto Delgado
  (her...@ru...)

-----Original Message-----
From: mes...@li...
[mailto:mes...@li...]On Behalf Of Stephen J
Baker
Sent: Jueves, 22 de Marzo de 2001 12:49 p.m.
To: io...@cr...
Cc: mes...@li...
Subject: Re: [Mesa3d-dev] Seriously off-topic question...


Oe Thu, 22 Mar 2001 her...@ru... wrote:

> 
> Hello! I'm really sorry if this question bothers you in any way, but it
> seems this
> is the only place I can ask it and actually receive a reasonable answer.

You'd stand a VERY good chance of getting an answer if you posted it to
the 'gdalgorithms' list.  They *thrive* on questions like this.

  gda...@li...

Subscribe at Sourceforge.

> Is there any way I can calculate the area of a triangle defined by his
> vertices  (x1,y1) - (x2,y2) - (x3,y3) WITHOUT the use of SQRT() in any
> part of the formula?

Yes.  (That was easy!)

...oh - you want to know *HOW* as well...OK.

Here are the steps needed to calculate the area of a 2D polygon. It
doesn't matter if the polygon is listed in a clockwise or
counter-clockwise order, it can be convex or concave, or even
self-intersect.

  /*
    x & y are arrays containing the x and y coordinates
    of the polygon vertices.

    npoints is the number of points in each list.
  */

  double area ( int npoints, double *x, double *y )
  {
    double area = 0.0 ;

    for ( int i = 0 ; i < npoints ; i++ )
    {
      int ii = (i+1) % npoints ;

      area += x[i] * y[ii] - x[ii] * y[i] ;
    }

    return fabs ( area / 2.0 ) ;
  }

----
Steve Baker                      (817)619-2657 (Vox/Vox-Mail)
L3Com/Link Simulation & Training (817)619-2466 (Fax)
Work: sj...@li...           http://www.link.com
Home: sjb...@ai...       http://web2.airmail.net/sjbaker1


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