/* Subroutine to calculate parameter values based on chord distances.

    C code for An Introduction to NURBS
    by David F. Rogers. Copyright (C) 2000 David F. Rogers,
    All rights reserved.
    
    Name: param.c
    Language: C
    Subroutines called: none
    Book reference: Alg. p. 295

    d[]        = array containing the data points
    dpts       = number of data points
    isum       = incremental sum of the chord distances 
    sum        = sum of all the chord distances
    tparm[]    = array containing the parameter values
*/

#include <math.h>

param(dpts,d,tparm)

int dpts;

float d[];
double tparm[];

{
    int i;
    int icount;

    float sum;
    float isum;
	float tempdx;
	float tempdy;
	float tempdz;

    sum = 0.;
    isum = 0.;
    tparm[1] = 0.;

/*    calculate the sum of the chord distances for all the data points */

    for (i = 1; i < 3*(dpts-1); i=i+3){
        tempdx = (d[i+3] - d[i])*(d[i+3] - d[i]);
        tempdy = (d[i+4] - d[i+1])*(d[i+4] - d[i+1]);
        tempdz = (d[i+5] - d[i+2])*(d[i+5] - d[i+2]);    
        sum = sum + sqrt(tempdx+tempdy+tempdz);
    }

/*    calculate the parameter values */

	icount = 2;

	for (i=1; i< 3*(dpts-1); i=i+3){
        tempdx = (d[i+3] - d[i])*(d[i+3] - d[i]);
        tempdy = (d[i+4] - d[i+1])*(d[i+4] - d[i+1]);
        tempdz = (d[i+5] - d[i+2])*(d[i+5] - d[i+2]);
        isum = isum + sqrt(tempdx+tempdy+tempdz);
        tparm[icount] = isum/sum;
		icount = icount + 1;
    }
}