# Get smoothing point using B-spline curve C++

I'm working on video stabilization topic. At the smoothing part, I need smooth parameters (translation, rotation+scale) by using B-spline curve for warping in order to create stabilized video.

Now, I am testing on some points. For example, I have 4 points (control points) with degree = 2, after using b-spline I wanna obtain 4 smoothed points. But when I use B-spline curve sample code in below, it created more than 4 points. I can not understand exactly that those results points which are belong to original points (control points). If I only get 4 points, the results is like as 4 original points (4 control points).How to get 4 smoothed points by using B-Spline curve?

Hope you guys help me to show this problem.

Here is the code.

```
#include "stdafx.h"
#include <stdio.h>
#include <conio.h>
/*
Subroutine to generate a B-spline open knot vector with multiplicity
equal to the order at the ends.
c = order of the basis function
n = the number of defining polygon vertices
nplus2 = index of x() for the first occurence of the maximum knot vector value
nplusc = maximum value of the knot vector -- $n + c$
x() = array containing the knot vector
*/
void knot(int n, int c, int x[])
{
int nplusc,nplus2,i;
nplusc = n + c;
nplus2 = n + 2;
x[1] = 0;
for (i = 2; i <= nplusc; i++){
if ( (i > c) && (i < nplus2) )
x[i] = x[i-1] + 1;
else
x[i] = x[i-1];
}
}
/* Subroutine to generate B-spline basis functions for open knot vectors
C code for An Introduction to NURBS
by David F. Rogers. Copyright (C) 2000 David F. Rogers,
All rights reserved.
Name: basis.c
Language: C
Subroutines called: none
Book reference: p. 279
c = order of the B-spline basis function
d = first term of the basis function recursion relation
e = second term of the basis function recursion relation
npts = number of defining polygon vertices
n[] = array containing the basis functions
n[1] contains the basis function associated with B1 etc.
nplusc = constant -- npts + c -- maximum number of knot values
t = parameter value
temp[] = temporary array
x[] = knot vector
*/
void basis(int c,float t, int npts,int x[],float n[])
{
int nplusc;
int i,k;
float d,e;
float temp[36];
nplusc = npts + c;
/* calculate the first order basis functions n[i][1] */
for (i = 1; i<= nplusc-1; i++){
if (( t >= x[i]) && (t < x[i+1]))
temp[i] = 1;
else
temp[i] = 0;
}
/* calculate the higher order basis functions */
for (k = 2; k <= c; k++){
for (i = 1; i <= nplusc-k; i++){
if (temp[i] != 0)/* if the lower order basis function is zero skip the calculation */
d = ((t-x[i])*temp[i])/(x[i+k-1]-x[i]);
else
d = 0;
if (temp[i+1] != 0) /* if the lower order basis function is zero skip the calculation */
e = ((x[i+k]-t)*temp[i+1])/(x[i+k]-x[i+1]);
else
e = 0;
temp[i] = d + e;
}
}
if (t == (float)x[nplusc]){ /* pick up last point */
temp[npts] = 1;
}
/* put in ...
```