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definetri.pro

Define a triangulation array like TRIANGULATE. But in a VERY SIMPLE CASE: the points are regulary-gridded on nx*ny array. Find a Delaunay triangulation for this set of points is easy: Points define (nx-1)*(ny-1) rectangles which we can cut in 2 triangles. cf. figure above
      ny-1*---*---*. . . . . .*---*---*
          |  +|  +|           |  +|  +|      
          | + | + |           | + | + |
          |+  |+  |           |+  |+  |
      ny-2*---*---*. . . . . .*---*---*   
          .       .           .       .
          .       .           .       .
          .       .           .       .
         1*---*---*. . . . . .*---*---*
          |  +|  +|           |  +|  +|
          | + | + |           | + | + |
          |+  |+  |           |+  |+  |
         0*---*---*. . . . . .*---*---*  
           0   1   2        nx-3  nx-2 nx-1
You have 2 ways to cut a rectangle: 1) the upward diagonal 2) the downward diagonal
          *---*                        *---*
          |  +|                        |+  |
          | + |                        | + |
          |+  |                        |  +|
          *---*                        *---*  

definetri Utilities

result = definetri(nx, ny[, downward])

Return value

triangles is a 2d array and is dimensions are 3 and 2*(nx-1)*(ny-1) triangles is define like in the TRIANGULATE procedure.

Parameters

nx        in required

The x dimension array

ny        in required

The y dimension array

downward        in optional

When downward is undefine all rectangles are cut in using the upward diagonal. Downward is a vector which contains the rectangles numbers which are cut in using the downward diagonal. The rectangle number is define by the index (in a nx*ny vector) of the lower-left corner of the rectangle.

Examples

triangles=definetri(3,3,[1,3]) triangles will be a this kind of triangulation: *---*---* |+ | +| | + | + | | +|+ | *---*---* | +|+ | | + | + | |+ | +| *---*---*

Version history

Version

$Id: definetri.pro 157 2006-08-21 09:01:50Z navarro $

History

sebastien Masson (smlod@ipsl.jussieu.fr) 4/3/1999

 


  Produced by IDLdoc 2.0 on Tue Aug 29 14:50:35 2006.