This is a simple library for differnent types of 1-D Splines, written for the arduino environment.

Checkout the code

git clone git://github.com/kerinin/arduino-splines.git ~/sketchbook/libraries/

Add the library header to your code

#include <spline.h>

There are currently 4 types of spline interpolation available:

1. Degree 0: This generates a step function. Between any two points the spline evaluates to the previous point

2. Degree 1: Linear interpolation. Between any two points the spline returns the value of a straight line connecting the bounding points

3. Hermite: Uses a Hermite spline to interpolate between the points. This method requires that you specify an array of tangent values m as well as the point arrays x and y.

4. Catmull: Uses a Catmull-Rom spline to interpolate between the points. This is an easy way to obtain smooth interpolation - you don't need to specify the tangent points.

Be aware that when using Catmull-Rom splines, the first and last points are not part of the spline - they are used to determine the tangency of the start and end of the spline. The spline itself starts at the second and second-to-last point.

For all splines, values requested outside the defined spline bounds will return the value of either the start or end point.

Using the library is fairly straightforward, simply pass it an array of points and use the value() function to interpolate between them. The spline points can be specified either when you instantiate the class or using the setPoints() and setDegree() functions.

double x[10] = {0,1,2,3,4,5,6,7,8,9};
double y[10] = {0,0,5,5,0,0,3,4,5,6};
doulbe m[10] = {0,.5,.5,.5.,.25,.25,.75,1,1,1}

Spline stepSpline(x,y,10,0);
Spline linearSpline(x,y,10,1);
Spline hermiteSpline(x,y,m,10);       // No neet to specify type since m passed
Spline catmullsSpline(x,y,10,Catmull);

stepSpline.value(5.5);    // => 0
linearSpline.value(5.5);  // => 1.5

Spline mySpline();
mySpline.setPoints(x,y);
mySpline.setDegree(1);

mySpline.value(5.5);      // => 1.5