All Identifiers

 THE IDTANG SUBROUTINE PERFORMS TRIANGULATION.  IT DIVIDES THE X-Y
 PLANE INTO A NUMBER OF TRIANGLES ACCORDING TO GIVEN DATA
 POINTS IN THE PLANE, DETERMINES LINE SEGMENTS THAT FORM THE
 BORDER OF DATA AREA, AND DETERMINES THE TRIANGLE NUMBERS
 CORRESPONDING TO THE BORDER LINE SEGMENTS.
 AT COMPLETION, POINT NUMBERS OF THE VERTEXES OF EACH TRIANGLE
 ARE LISTED COUNTER-CLOCKWISE.  POINT NUMBERS OF THE END POINTS
 OF EACH BORDER LINE SEGMENT ARE LISTED COUNTER-CLOCKWISE,
 LISTING ORDER OF THE LINE SEGMENTS BEING COUNTER-CLOCKWISE.
 THIS SUBROUTINE CALLS THE IDXCHG FUNCTION.

 THE INPUT PARAMETERS ARE
     NDP = NUMBER OF DATA POINTS,
     XD  = ARRAY OF DIMENSION NDP CONTAINING THE
           X COORDINATES OF THE DATA POINTS,
     YD  = ARRAY OF DIMENSION NDP CONTAINING THE
           Y COORDINATES OF THE DATA POINTS.
 THE OUTPUT PARAMETERS ARE
     NT  = NUMBER OF TRIANGLES,
     IPT = INTEGER ARRAY OF DIMENSION 6*NDP-15, WHERE THE
           POINT NUMBERS OF THE VERTEXES OF THE (IT)TH
           TRIANGLE ARE TO BE STORED AS THE (3*IT-3)ND,
           (3*IT-2)ST, AND (3*IT-1)TH ELEMENTS,
           IT=1,2,...,NT,
     NL  = NUMBER OF BORDER LINE SEGMENTS,
     IPL = INTEGER ARRAY OF DIMENSION 6*NDP, WHERE THE
           POINT NUMBERS OF THE END POINTS OF THE (IL)TH
           BORDER LINE SEGMENT AND ITS RESPECTIVE TRIANGLE
           NUMBER ARE TO BE STORED AS THE (3*IL-2)ND,
           (3*IL-1)ST, AND (3*IL)TH ELEMENTS,
           IL=1,2,..., NL.

 THE OTHER PARAMETERS ARE
     IWL = INTEGER ARRAY OF DIMENSION 18*NDP USED
           INTERNALLY AS A WORK AREA,
     IWP = INTEGER ARRAY OF DIMENSION NDP USED
           INTERNALLY AS A WORK AREA,
     WK  = ARRAY OF DIMENSION NDP USED INTERNALLY AS A
           WORK AREA.