Package org.faceless.graph.math

Class Spline

  • public class Spline
extends FunctionCurve

    Create a Spline Curve, or more accurately a sequence of spline curves which can be used to interpolate or approximate, or just plain "Smooth" a DataCurve.

    Currently this class provides two pre-defined spline curves which can be mapped to a collection of data points.

    A Catmull-Rom spline is a spline curve which passes through every point on the DataCurve, guaranteed.
    A B-Spline is a spline curve which approximates the data points it's based on. A B-Spline may not pass through any of the points supplied, but will tend to lessen the influence of "spikes" in the data. B-Splines conventionally use the first and last points as control points only. This class generates useful values for the first and last points on the DataCurve by repeating the first and last values in the data set.

    The curves are defined by the basis matrix for the spline. If the basis matrix has less rows than the number of points in the datacurve, several curves are "patched" together, using the n points of the datacurve starting at point 0, then point 1, then point 2 and so on.

    If you haven't understood a word of this, you failed calculus at school, but you still still want your curves to be nice and smooth, just use a Catmull-Rom spline like this: 

       DataCurve data = new DataCurve();
   data.add(x,y);                       // Add data to the curve
     .
     .
   Curve smooth = new Spline(Spline.CATMULLROM, data);
    See Also:
    Matrix, DataCurve

    • Field Summary

      Fields 
      Modifier and Type Field Description
      static Matrix BSPLINE
      Defines the basis matrix for a B-spline
      static Matrix CATMULLROM
      Defines the basis matrix for a Catmull-Rom spline

    • Constructor Summary

      Constructors 
      Constructor Description
      Spline​(Matrix matrix, double[] x, double[] y)
      Return a new Spline curve of the specified type fitted to the array of X and Y values supplied.
      Spline​(Matrix matrix, DataCurve d)
      Return a new Spline curve of the specified type fitted to the supplied DataCurve.

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      double get​(double x)
      Return the value of the spline at the specified X value.
      double getMax()
      Return the maximum value that is defined for this curve.
      double getMin()
      Return the minimum value that is defined for this curve.
      boolean point​(double x)
      If a marker is to be placed at this point on the curve then return true, otherwise return false.
      double[] steps()
      Return the points on the curve that it should be sampled at to get an accurate picture of it.

      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

    • Field Detail

      • CATMULLROM

        public static final Matrix CATMULLROM
        Defines the basis matrix for a Catmull-Rom spline

      • BSPLINE

        public static final Matrix BSPLINE
        Defines the basis matrix for a B-spline

    • Constructor Detail

      • Spline

        public Spline​(Matrix matrix,
              DataCurve d)
        Return a new Spline curve of the specified type fitted to the supplied DataCurve.
        Parameters:
        matrix - The basis matrix for the curve. May be CATMULLROM, BSPLINE or a user-defined 4x4 matrix.
        d - the data-curve to fit to.

      • Spline

        public Spline​(Matrix matrix,
              double[] x,
              double[] y)
        Return a new Spline curve of the specified type fitted to the array of X and Y values supplied. Note that although a Spline may loop back on itself (i.e. for any X position there may be more than one Y value) this class does not account for it (as it's meaning is to smooth curves, not provide a fully fledged spline interpolator). The results are undefined if the data passed in loops back upon itself.
        Parameters:
        matrix - The basis matrix for the curve. May be CATMULLROM, BSPLINE or a user-defined matrix.
        x - the X values to fit the curve to
        y - the Y values to fit the curve to

    • Method Detail

      • get

        public double get​(double x)
        Return the value of the spline at the specified X value. Note that unlike other spline libraries you may encounter, the value supplied is not the position along the length of the curve, but the position on the X axis. Remember this class is intended only for use with Line Graphs, not for general spline interpolation.
        Specified by:
        get in class Curve

      • getMin

        public double getMin()
        Description copied from class: Curve
        Return the minimum value that is defined for this curve. For curves with no minimum (like most mathematical functions), this should return Double.POSITIVE_INFINITY (yes, positive)
        Overrides:
        getMin in class FunctionCurve

      • getMax

        public double getMax()
        Description copied from class: Curve
        Return the maximum value that is defined for this curve. For curves with no maximum (like most mathematical functions), this should return Double.NEGATIVE_INFINITY (yes, negative)
        Overrides:
        getMax in class FunctionCurve

      • steps

        public double[] steps()
        Description copied from class: Curve
        Return the points on the curve that it should be sampled at to get an accurate picture of it. Subclasses of FunctionCurve may return an empty list if they wish, or if there are certain points that the curve must be sampled at, it can return them here.
        Overrides:
        steps in class FunctionCurve

      • point

        public boolean point​(double x)
        Description copied from class: Curve
        If a marker is to be placed at this point on the curve then return true, otherwise return false. Most FunctionCurve will return false, but curves that have been fitted to a DataCurve may return any points from that DataCurve that are matched exactly by the fitted curve.
        Overrides:
        point in class FunctionCurve