org.eclipse.dawnsci.analysis.dataset.roi.fitting.AngleDerivativeFunction.java Source code

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Here is the source code for org.eclipse.dawnsci.analysis.dataset.roi.fitting.AngleDerivativeFunction.java

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/*-
 *******************************************************************************
 * Copyright (c) 2011, 2014 Diamond Light Source Ltd.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *    Peter Chang - initial API and implementation and/or initial documentation
 *******************************************************************************/

package org.eclipse.dawnsci.analysis.dataset.roi.fitting;

import java.io.Serializable;

import org.apache.commons.math3.analysis.UnivariateFunction;

/**
 * This class represents the derivative with respect to angle of the geometric
 * distance function from a given point to an ellipse. It is used by an optimizer
 * to find the closest point on an ellipse to a given point.
 * <p>
 * The ellipse is centred on the origin.
 */
public class AngleDerivativeFunction implements UnivariateFunction, Serializable {
    double ra, rb; // major and minor semi-axes
    double alpha; // orientation angle of major axis
    double A, B, C;

    /**
     * Set major and minor semi-axes of ellipse
     */
    public void setRadii(final double a, final double b) {
        ra = a;
        rb = b;
        A = ra * ra - rb * rb;
    }

    /**
     * Set angle of major axis of ellipse
     * @param angle
     */
    public void setAngle(final double angle) {
        alpha = angle;
    }

    /**
     * Set coordinates of given point
     * @param Xc
     * @param Yc
     */
    public void setCoordinate(final double Xc, final double Yc) {
        final double c = Math.cos(alpha);
        final double s = Math.sin(alpha);
        B = -ra * (Xc * c + Yc * s);
        C = -rb * (Xc * s - Yc * c);
    }

    /**
     * @return value proportional to the derivative of the distance function wrt. angle
     */
    @Override
    public double value(final double angle) {
        final double c = Math.cos(angle);
        final double s = Math.sin(angle);

        return (A * c + B) * s + C * c; // -ve and 1/2 value of squared distance derivative
    }
}