isintriangle

  determine if point (x0,y0) is in triangle defined by nodes (xt(3),yt(3))    

  function res = isintriangle(xt,yt,x0,y0)

  determine if point (x0,y0) is in triangle defined by nodes (xt(3),yt(3))    |
  using algorithm used for scene rendering in computer graphics               |
  algorithm works well unless particle happens to lie in a line parallel      |
  to the edge of a triangle.                                                  |
  This can cause problems if you use a regular grid, say for idealized        |
  modelling and you happen to seed particles right on edges or parallel to    |
  edges.                                                                      |
==============================================================================|

0001 function res = isintriangle(xt,yt,x0,y0)
0002 %  determine if point (x0,y0) is in triangle defined by nodes (xt(3),yt(3))
0003 %
0004 %  function res = isintriangle(xt,yt,x0,y0)
0005 %
0006 %  determine if point (x0,y0) is in triangle defined by nodes (xt(3),yt(3))    |
0007 %  using algorithm used for scene rendering in computer graphics               |
0008 %  algorithm works well unless particle happens to lie in a line parallel      |
0009 %  to the edge of a triangle.                                                  |
0010 %  This can cause problems if you use a regular grid, say for idealized        |
0011 %  modelling and you happen to seed particles right on edges or parallel to    |
0012 %  edges.                                                                      |
0013 %==============================================================================|
0014 
0015  res = 0;
0016  f1 = (y0-yt(1))*(xt(2)-xt(1)) - (x0-xt(1))*(yt(2)-yt(1));
0017  f2 = (y0-yt(3))*(xt(1)-xt(3)) - (x0-xt(3))*(yt(1)-yt(3));
0018  f3 = (y0-yt(2))*(xt(3)-xt(2)) - (x0-xt(2))*(yt(3)-yt(2));
0019  if(f1*f3 >= 0.0 & f3*f2 >= 0.0) 
0020    res = 1;
0021  end;
0022 
0023  return
0024