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75 lines
2.1 KiB
75 lines
2.1 KiB
2 years ago
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C Copyright(C) 1999-2020 National Technology & Engineering Solutions
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C of Sandia, LLC (NTESS). Under the terms of Contract DE-NA0003525 with
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C NTESS, the U.S. Government retains certain rights in this software.
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C
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C See packages/seacas/LICENSE for details
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SUBROUTINE VINTER (MXND, XN, YN, N1, N2, N3, XOLD, YOLD,
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& XNEW, YNEW, VCROSS)
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C***********************************************************************
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C SUBROUTINE VINTER = FINDS WHERE A VECTOR FROM N1 TO N2
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C INTERSECTS THE VECTOR FROM N3 TO (XOLD, YOLD)
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C***********************************************************************
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C NOTE: THIS INTERSECTION ROUTINE IS BASED ON AN ALGORITHM GIVEN
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C IN THE BOOK "GEOMETRIC MODELING" BY MICHAEL E. MORTENSON ON
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C PAGES 319 - 320.
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C***********************************************************************
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DIMENSION XN (MXND), YN (MXND)
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LOGICAL VCROSS
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VCROSS = .FALSE.
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C SET UP THE FIRST LINE'S VECTORS (A AND B)
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XA = XN (N1)
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YA = YN (N1)
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XB = XN (N2) - XN (N1)
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YB = YN (N2) - YN (N1)
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C SET UP THE SECOND LINE'S VECTORS (C AND D)
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XC = XN (N3)
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YC = YN (N3)
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XD = XOLD - XN (N3)
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YD = YOLD - YN (N3)
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C NOW USE THE VECTORS AND SOLVE FOR W.
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C W IS THE PROPORTION OF THE DISTANCE ALONG THE VECTOR D
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C WHERE THE INTERSECTION OCCURS. LIKEWISE U IS THE PROPORTIONAL
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C DISTANCE ALONG THE VECTOR B FOR THE INTERSECTION.
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DENOM = (YB * XD) - (XB * YD)
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C CHECK FOR SPECIAL PARALLEL CASE - THE DENOMINATOR IS EQUAL TO ZERO.
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IF (DENOM .NE. 0.) THEN
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C GET INTERSECTION LOCATION
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W = ( (YC * XB) - (XB * YA) - (XC * YB) + (YB * XA) ) / DENOM
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C GET THE U VALUE TO CONFIRM.
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IF (XB .NE. 0.) THEN
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U = ( XC + (W * XD) - XA ) / XB
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ELSE
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U = ( YC + (W * YD) - YA ) / YB
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ENDIF
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C CALCULATE THE INTERSECTION POINT BASED ON SIMILAR TRIANGLES
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XNEW = ( (XA + (XB * U)) + (XC + (XD * W)) ) * .5
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YNEW = ( (YA + (YB * U)) + (YC + (YD * W)) ) * .5
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VCROSS = .TRUE.
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ENDIF
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RETURN
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END
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