001/*******************************************************************************
002 * This software is provided as a supplement to the authors' textbooks on digital
003 * image processing published by Springer-Verlag in various languages and editions.
004 * Permission to use and distribute this software is granted under the BSD 2-Clause
005 * "Simplified" License (see http://opensource.org/licenses/BSD-2-Clause).
006 * Copyright (c) 2006-2023 Wilhelm Burger, Mark J. Burge. All rights reserved.
007 * Visit https://imagingbook.com for additional details.
008 ******************************************************************************/
009package imagingbook.common.geometry.fitting.line.utils;
010
011import imagingbook.common.geometry.basic.Pnt2d;
012
013import java.util.Random;
014
015/**
016 * <p>
017 * Instances of this class are used to randomly sample points along a given straight line segment, x/y coordinates being
018 * perturbed with Gaussian noise. Mainly used for testing line fitters.
019 * </p>
020 *
021 * @author WB
022 * @version 2022/09/29
023 */
024public class LineSampler {
025        
026        private final Random rg;
027        private final Pnt2d p1, p2;
028        
029        /**
030         * Constructor (with no specific seed).
031         * @param p1 first point of the line segment
032         * @param p2 second point of the line segment
033         */
034        public LineSampler(Pnt2d p1, Pnt2d p2) {
035                this(p1, p2, 0);
036        }
037        
038        /**
039         * Constructor (with specific random seed).
040         * @param p1 first point of the line segment
041         * @param p2 second point of the line segment
042         * @param seed random seed (pass 0 for complete randomness)
043         */
044        public LineSampler(Pnt2d p1, Pnt2d p2, long seed) {
045                this.p1 = p1;
046                this.p2 = p2;
047                this.rg = (seed == 0) ? new Random() : new Random(seed);
048        }
049        
050        /**
051         * Returns an array of randomly sampled points.
052         * @param n the number of points
053         * @param sigma standard deviation of Gaussian position noise
054         * @return an array of random points
055         */
056        public Pnt2d[] getPoints(int n, double sigma) {
057                double dx = p2.getX() - p1.getX();
058                double dy = p2.getY() - p1.getY();              
059                Pnt2d[] pts = new Pnt2d[n];
060                
061                for (int i = 0; i < n; i++) {
062                        double x = p1.getX() + dx * i / n + rg.nextGaussian() * sigma;
063                        double y = p1.getY() + dy * i / n + rg.nextGaussian() * sigma;
064                        pts[i] = Pnt2d.from(x, y);
065                }
066                
067                return pts;
068        }
069
070}