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#ifndef lint
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static const char RCSid[] = "$Id: hermite3.c,v 2.3 2003/06/08 12:03:09 schorsch Exp $";
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#endif
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/*
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* hermite.c - routines for 3D hermite curves.
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*
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* 10/29/85
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*/
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#include <stdio.h>
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void
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hermite3( /* compute point on hermite curve */
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double hp[3], /* returned hermite point */
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double p0[3], /* first endpoint */
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double p1[3], /* second endpoint */
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double r0[3], /* tangent at p0 */
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double r1[3], /* tangent at p1 */
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double t /* position parameter */
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)
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{
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register int i;
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double tmh[4];
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tmh[0] = (2.0*t - 3.0)*t*t + 1.0;
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tmh[1] = (-2.0*t + 3.0)*t*t;
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tmh[2] = ((t - 2.0)*t + 1.0)*t;
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tmh[3] = (t - 1.0)*t*t;
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for (i = 0; i < 3; i++)
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hp[i] = p0[i]*tmh[0] + p1[i]*tmh[1] +
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r0[i]*tmh[2] + r1[i]*tmh[3];
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}
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void
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htan3( /* compute tangent on hermite curve */
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double ht[3], /* returned hermite tangent */
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double p0[3], /* first endpoint */
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double p1[3], /* second endpoint */
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double r0[3], /* tangent at p0 */
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double r1[3], /* tangent at p1 */
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double t /* position parameter */
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)
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{
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register int i;
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double tpmh[4];
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tpmh[0] = (6.0*t - 6.0)*t;
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tpmh[1] = (-6.0*t + 6.0)*t;
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tpmh[2] = (3.0*t - 4.0)*t + 1.0;
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tpmh[3] = (3.0*t - 2.0)*t;
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for (i = 0; i < 3; i++)
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ht[i] = p0[i]*tpmh[0] + p1[i]*tpmh[1] +
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r0[i]*tpmh[2] + r1[i]*tpmh[3];
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}
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