[2] | 1 | ;+ |
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| 2 | ; NAME:definetri |
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| 3 | ; |
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| 4 | ; PURPOSE:Define a triangulation array like TRIANGULATE. |
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| 5 | ; But in a VERY SIMPLE CASE: |
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| 6 | ; the points are regulary-gridded on nx*ny array. |
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| 7 | ; Find a Delaunay triangulation for this set of points is easy: |
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| 8 | ; Points define (nx-1)*(ny-1) rectangles which we can cut in 2 |
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| 9 | ; triangles. cf. figure above |
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| 10 | ; |
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| 11 | ; |
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| 12 | ; ny-1*---*---*. . . . . .*---*---* |
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| 13 | ; | /| /| | /| /| |
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| 14 | ; | / | / | | / | / | |
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| 15 | ; |/ |/ | |/ |/ | |
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| 16 | ; ny-2*---*---*. . . . . .*---*---* |
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| 17 | ; . . . . |
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| 18 | ; . . . . |
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| 19 | ; . . . . |
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| 20 | ; 1*---*---*. . . . . .*---*---* |
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| 21 | ; | /| /| | /| /| |
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| 22 | ; | / | / | | / | / | |
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| 23 | ; |/ |/ | |/ |/ | |
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| 24 | ; 0*---*---*. . . . . .*---*---* |
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| 25 | ; 0 1 2 nx-3 nx-2 nx-1 |
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| 26 | ; |
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| 27 | ; You have 2 ways to cut a rectangle: |
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| 28 | ; 1) the upward diagonal 2) the downward diagonal |
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| 29 | ; |
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| 30 | ; *---* *---* |
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| 31 | ; | /| |\ | |
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| 32 | ; | / | | \ | |
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| 33 | ; |/ | | \| |
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| 34 | ; *---* *---* |
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| 35 | ; |
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| 36 | ; |
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| 37 | ; CATEGORY: to understand how TRIANGULATE and TRIANGULATION work! |
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| 38 | ; |
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| 39 | ; CALLING SEQUENCE:triangles=definetri(nx, ny [,downward]) |
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| 40 | ; |
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| 41 | ; INPUTS: nx and ny are the array dimensions |
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| 42 | ; |
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| 43 | ; OPTIONAL INPUTS: |
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| 44 | ; |
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| 45 | ; downward: When downward is undefine all rectangles are cut |
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| 46 | ; in using the upward diagonal. Downward is a vector which |
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| 47 | ; contains the rectangles numbers which are cut in using the |
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| 48 | ; downward diagonal. |
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| 49 | ; The rectangle number is define by the index (in a nx*ny |
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| 50 | ; vector) of the lower-left corner of the rectangle. |
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| 51 | ; |
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| 52 | ; KEYWORD PARAMETERS: |
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| 53 | ; |
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| 54 | ; OUTPUTS: |
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| 55 | ; triangles is a 2d array and is dimensions are 3 and |
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| 56 | ; 2*(nx-1)*(ny-1) |
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| 57 | ; triangles is define like in the TRIANGULATE procedure. |
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| 58 | ; |
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| 59 | ; |
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| 60 | ; OPTIONAL OUTPUTS: |
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| 61 | ; |
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| 62 | ; COMMON BLOCKS: |
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| 63 | ; |
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| 64 | ; SIDE EFFECTS: |
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| 65 | ; |
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| 66 | ; RESTRICTIONS: |
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| 67 | ; |
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| 68 | ; PROCEDURE: |
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| 69 | ; |
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| 70 | ; EXAMPLE: |
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| 71 | ; |
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| 72 | ; triangles=definetri(3,3,[1,3]) |
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| 73 | ; triangles will be a this kind of triangulation: |
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| 74 | ; |
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| 75 | ; *---*---* |
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| 76 | ; |\ | /| |
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| 77 | ; | \ | / | |
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| 78 | ; | \|/ | |
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| 79 | ; *---*---* |
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| 80 | ; | /|\ | |
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| 81 | ; | / | \ | |
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| 82 | ; |/ | \| |
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| 83 | ; *---*---* |
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| 84 | ; |
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| 85 | ; |
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| 86 | ; MODIFICATION HISTORY: sebastien Masson (smlod@ipsl.jussieu.fr) |
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| 87 | ; 4/3/1999 |
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| 88 | ; |
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| 89 | ;- |
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| 90 | FUNCTION definetri, nx, ny, downward |
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[114] | 91 | ; |
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| 92 | compile_opt idl2, strictarrsubs |
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| 93 | ; |
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[2] | 94 | nx = long(nx) |
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| 95 | ny = long(ny) |
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| 96 | if n_elements(downward) NE 0 THEN BEGIN |
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| 97 | if n_elements(downward) GT (nx-1)*(ny-1) then begin |
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| 98 | print, 'downward a trop d''elements par rapport a nx et ny!' |
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| 99 | return, -1 |
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| 100 | endif |
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| 101 | downward = long(downward) |
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| 102 | ENDIF |
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| 103 | ; we define triangles |
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| 104 | triangles = lonarr(3, 2*(nx-1)*(ny-1)) |
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| 105 | ;---------------------------------------------------------------------------------- |
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| 106 | ; we cut the rectangles with the upward diagonal |
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| 107 | ;---------------------------------------------------------------------------------- |
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| 108 | if n_elements(downward) NE (nx-1)*(ny-1) then BEGIN ; there is some rectangle to cut. |
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| 109 | ; we define upward: upward is a vector which contains the rectangles |
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| 110 | ; numbers which are cut in using the upward diagonal. |
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| 111 | ; The rectangle number is define by the index (in a nx*ny vector) of |
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| 112 | ; the lower-left corner of the rectangle. |
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| 113 | upward = bytarr(nx, ny)+1 |
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[114] | 114 | upward[*, ny-1] = 0 |
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| 115 | upward[nx-1, *] = 0 |
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[2] | 116 | if n_elements(downward) NE 0 then upward[downward] = 0 |
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| 117 | upward = where(upward EQ 1) |
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| 118 | n1 = n_elements(upward) |
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| 119 | ; |
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| 120 | ; 4 corners indexes of a rectangle number i are |
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| 121 | ; |
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| 122 | ; i+nx i+nx+1 |
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| 123 | ; *---* |
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| 124 | ; | /| |
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| 125 | ; | / | |
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| 126 | ; |/ | |
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| 127 | ; *---* |
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| 128 | ; i i+1 |
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| 129 | ; |
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| 130 | trinumber = 2*(upward-upward/nx) |
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| 131 | ;; we define the right triangles |
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| 132 | triangles[0, trinumber] = upward |
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| 133 | triangles[1, trinumber] = upward+1 |
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| 134 | triangles[2, trinumber] = upward+1+nx |
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| 135 | ; we define the left triangles |
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| 136 | triangles[0, trinumber+1] = upward+1+nx |
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| 137 | triangles[1, trinumber+1] = upward+nx |
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| 138 | triangles[2, trinumber+1] = upward |
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| 139 | ENDIF ELSE n1 = 0 |
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| 140 | ;---------------------------------------------------------------------------------- |
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| 141 | ; we cut the rectangles with the downward diagonal |
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| 142 | ;---------------------------------------------------------------------------------- |
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| 143 | if n_elements(downward) NE 0 then BEGIN |
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| 144 | n2 = n_elements(downward) |
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| 145 | trinumber = 2*(downward-downward/nx) |
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| 146 | ; we define the right triangles |
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| 147 | triangles[0, trinumber] = downward+1 |
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| 148 | triangles[1, trinumber] = downward+nx+1 |
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| 149 | triangles[2, trinumber] = downward+nx |
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| 150 | ; we define the left triangles |
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| 151 | triangles[0, trinumber+1] = downward+nx |
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| 152 | triangles[1, trinumber+1] = downward |
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| 153 | triangles[2, trinumber+1] = downward+1 |
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| 154 | endif |
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| 155 | |
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| 156 | return, triangles |
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| 157 | end |
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