Application: gvSIG desktop » gvSIG tools: Vector editing

/* gvSIG. Desktop Geographic Information System.

 *

 * Copyright ? 2007-2016 gvSIG Association

 *

 * This program is free software; you can redistribute it and/or

 * modify it under the terms of the GNU General Public License

 * as published by the Free Software Foundation; either version 2

 * of the License, or (at your option) any later version.

 *

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,

 * MA  02110-1301, USA.

 *

 * For any additional information, do not hesitate to contact us

 * at info AT gvsig.com, or visit our website www.gvsig.com.

 */

package org.gvsig.vectorediting.lib.prov.editvertex.operation;

/**

 * @author fdiaz

 *

 */

public class SplineCalculator {

    private final double y[];

    private final double y2[];

    /**

     * The constructor calculates the second derivatives of the interpolating function

     * at the tabulated points xi, with xi = (i, y[i]).

     * Based on numerical recipes in C, http://www.library.cornell.edu/nr/bookcpdf/c3-3.pdf .

     * @param y Array of y coordinates for cubic-spline interpolation.

     */

    public SplineCalculator(double y[]) {

        this.y = y;

        int n = y.length;

        y2 = new double[n];

        double u[] = new double[n];

        for (int i = 1; i < n - 1; i++) {

            y2[i] = -1.0 / (4.0 + y2[i - 1]);

            u[i] = (6.0 * (y[i + 1] - 2.0 * y[i] + y[i - 1]) - u[i - 1]) / (4.0 + y2[i - 1]);

        }

        for (int i = n - 2; i >= 0; i--) {

            y2[i] = y2[i] * y2[i + 1] + u[i];

        }

    }

    /**

     * Returns a cubic-spline interpolated value y for the point between

     * point (n, y[n]) and (n+1, y[n+1), with t ranging from 0 for (n, y[n])

     * to 1 for (n+1, y[n+1]).

     * @param n The start point.

     * @param t The distance to the next point (0..1).

     * @return A cubic-spline interpolated value.

     */

    public double fn(int n, double t) {

        return t * y[n + 1] - ((t - 1.0) * t * ((t - 2.0) * y2[n] - (t + 1.0) * y2[n + 1])) / 6.0 + y[n] - t * y[n];

    }

}