a point inside polygon

[rolz]

I've got stuck with a math question.

How to determine Z coordinate for a point inside a polygon with given x and y coordinates ?

Assume we have SimpleVector p1, p2, p3 - vertices of the polygon.
then we have float x, float y - coordinates of point inside this polygon. How do we find Z coordinate that belongs to this polygon ?

Spent 30 minutes trying to figure this out and finally gave up. .. any suggestions ?

[EgonOlsen]

Maybe like so...(but i'm not sure as i don't have a valid test case for this. I've just done this on paper and i can hardly read my own writings...:wink: ):

Code Select Expand

import com.threed.jpct.*;

public class TestPoint {
 public static void main(String[] args) {

   // The vertices
   SimpleVector p0=new SimpleVector(10,10,40);
   SimpleVector p1=new SimpleVector(0,10,20);
   SimpleVector p2=new SimpleVector(10,0,10);

   // The "target" vertex
   SimpleVector px=new SimpleVector(10,0,0);

   // The vectors from p0 to the other vertices
   SimpleVector a=p1.calcSub(p0);
   SimpleVector b=p2.calcSub(p0);

   float d=0.00000000001f;
   float div=(b.y*a.x-b.x*a.y);
   float div2=a.y;
   if (div==0) {
     div=d;
   }

   if (div2==0) {
     div2=d;
   }

   // Some linear algebra...could be just plain wrong...:-)
   float y=((-p0.y+px.y)*a.x+(p0.x-px.x)*a.y)/div;
   float x=(-p0.y+px.y-y*b.y)/div2;

   px.z=p0.z+x*a.z+y*b.z;

   System.out.println(px);
 }
}


[EgonOlsen]

Have you tried it? Did it work?

[rolz]

Sorry for late response. Nope, it didnt worked. Sometimes player flies over the ground, sometimes falls through.

[rolz]

My bad, i was putting vertices in wrong order. It works now Thanks !