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Java example source code file (CannonballExample.java)

This example Java source code file (CannonballExample.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

arial, arraylist, awt, cannonball, chart, display, exampleframe, font, gui, jcomponent, jpanel, kalmanfilter, list, realmatrix, realvector, swing, util

The CannonballExample.java Java example source code

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements. See the NOTICE file distributed with this
 * work for additional information regarding copyright ownership. The ASF
 * licenses this file to You under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law
 * or agreed to in writing, software distributed under the License is
 * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied. See the License for the specific language
 * governing permissions and limitations under the License.
 */

package org.apache.commons.math3.userguide.filter;

import java.awt.Color;
import java.awt.Component;
import java.awt.Font;
import java.util.ArrayList;
import java.util.List;

import javax.swing.BorderFactory;
import javax.swing.BoxLayout;
import javax.swing.JComponent;
import javax.swing.JPanel;

import org.apache.commons.math3.filter.DefaultMeasurementModel;
import org.apache.commons.math3.filter.DefaultProcessModel;
import org.apache.commons.math3.filter.KalmanFilter;
import org.apache.commons.math3.filter.MeasurementModel;
import org.apache.commons.math3.filter.ProcessModel;
import org.apache.commons.math3.linear.MatrixUtils;
import org.apache.commons.math3.linear.RealMatrix;
import org.apache.commons.math3.linear.RealVector;
import org.apache.commons.math3.random.RandomGenerator;
import org.apache.commons.math3.random.Well19937c;
import org.apache.commons.math3.userguide.ExampleUtils;
import org.apache.commons.math3.userguide.ExampleUtils.ExampleFrame;
import org.apache.commons.math3.util.FastMath;

import com.xeiam.xchart.Chart;
import com.xeiam.xchart.ChartBuilder;
import com.xeiam.xchart.Series;
import com.xeiam.xchart.SeriesLineStyle;
import com.xeiam.xchart.SeriesMarker;
import com.xeiam.xchart.XChartPanel;
import com.xeiam.xchart.StyleManager.ChartType;
import com.xeiam.xchart.StyleManager.LegendPosition;

public class CannonballExample {

    public static class Cannonball {
    
        private final double[] gravity = { 0, -9.81 };
        private final double[] velocity;
        private final double[] location;
        
        private final double timeslice;
        private final double measurementNoise;
        
        private final RandomGenerator rng;
        
        public Cannonball(double timeslice, double angle, double initialVelocity, double measurementNoise, int seed) {
            this.timeslice = timeslice;
            
            final double angleInRadians = FastMath.toRadians(angle);
            this.velocity = new double[] {
                    initialVelocity * FastMath.cos(angleInRadians),
                    initialVelocity * FastMath.sin(angleInRadians)
            };
            
            this.location = new double[] { 0, 0 };
            
            this.measurementNoise = measurementNoise;
            this.rng = new Well19937c(seed);
        }
        
        public double getX() {
            return location[0];
        }
        
        public double getY() {
            return location[1];
        }

        public double getMeasuredX() {
            return location[0] + rng.nextGaussian() * measurementNoise;
        }

        public double getMeasuredY() {
            return location[1] + rng.nextGaussian() * measurementNoise;
        }

        public double getXVelocity() {
            return velocity[0];
        }
        
        public double getYVelocity() {
            return velocity[1];
        }
        
        public void step() {
            // Break gravitational force into a smaller time slice.
            double[] slicedGravity = gravity.clone();
            for ( int i = 0; i < slicedGravity.length; i++ ) {
                slicedGravity[i] *= timeslice;
            }
            
            // Apply the acceleration to velocity.
            double[] slicedVelocity = velocity.clone();
            for ( int i = 0; i < velocity.length; i++ ) {
                velocity[i] += slicedGravity[i];
                slicedVelocity[i] = velocity[i] * timeslice;
                location[i] += slicedVelocity[i];
            }

            // Cannonballs shouldn't go into the ground.
            if ( location[1] < 0 ) {
                location[1] = 0;
            }
        }
    }
    
    public static void cannonballTest(Chart chart) {
        
        // time interval for each iteration
        final double dt = 0.1;
        // the number of iterations to run
        final int iterations = 144;
        // measurement noise (m)
        final double measurementNoise = 30;
        // initial velocity of the cannonball
        final double initialVelocity = 100;
        // shooting angle
        final double angle = 45;

        // the cannonball itself
        final Cannonball cannonball = new Cannonball(dt, angle, initialVelocity, measurementNoise, 1000);
        
        // A = [ 1, dt, 0,  0 ]  =>  x(n+1) = x(n) + vx(n)
        //     [ 0,  1, 0,  0 ]  => vx(n+1) =        vx(n)
        //     [ 0,  0, 1, dt ]  =>  y(n+1) =              y(n) + vy(n)
        //     [ 0,  0, 0,  1 ]  => vy(n+1) =                     vy(n)
        final RealMatrix A = MatrixUtils.createRealMatrix(new double[][] {
                { 1, dt, 0,  0 },
                { 0,  1, 0,  0 },
                { 0,  0, 1, dt },
                { 0,  0, 0,  1 }       
        });

        // The control vector, which adds acceleration to the kinematic equations.
        // 0          =>  x(n+1) =  x(n+1)
        // 0          => vx(n+1) = vx(n+1)
        // -9.81*dt^2 =>  y(n+1) =  y(n+1) - 1/2 * 9.81 * dt^2
        // -9.81*dt   => vy(n+1) = vy(n+1) - 9.81 * dt
        final RealVector controlVector =
                MatrixUtils.createRealVector(new double[] { 0, 0, 0.5 * -9.81 * dt * dt, -9.81 * dt } );

        // The control matrix B only update y and vy, see control vector
        final RealMatrix B = MatrixUtils.createRealMatrix(new double[][] {
                { 0, 0, 0, 0 },
                { 0, 0, 0, 0 },
                { 0, 0, 1, 0 },
                { 0, 0, 0, 1 }
        });

        // After state transition and control, here are the equations:
        //
        //  x(n+1) = x(n) + vx(n)
        // vx(n+1) = vx(n)
        //  y(n+1) = y(n) + vy(n) - 0.5 * 9.81 * dt^2
        // vy(n+1) = vy(n) + -9.81 * dt
        //
        // Which, if you recall, are the equations of motion for a parabola.

        // We only observe the x/y position of the cannonball
        final RealMatrix H = MatrixUtils.createRealMatrix(new double[][] {
                { 1, 0, 0, 0 },
                { 0, 0, 0, 0 },
                { 0, 0, 1, 0 },
                { 0, 0, 0, 0 }
        });
        
        // This is our guess of the initial state.  I intentionally set the Y value
        // wrong to illustrate how fast the Kalman filter will pick up on that.
        final double speedX = cannonball.getXVelocity();
        final double speedY = cannonball.getYVelocity();
        final RealVector initialState = MatrixUtils.createRealVector(new double[] { 0, speedX, 100, speedY } );

        // The initial error covariance matrix, the variance = noise^2
        final double var = measurementNoise * measurementNoise;
        final RealMatrix initialErrorCovariance = MatrixUtils.createRealMatrix(new double[][] {
                { var,    0,   0,    0 },
                {   0, 1e-3,   0,    0 },
                {   0,    0, var,    0 },
                {   0,    0,   0, 1e-3 }
        });

        // we assume no process noise -> zero matrix
        final RealMatrix Q = MatrixUtils.createRealMatrix(4, 4);
        
        // the measurement covariance matrix
        final RealMatrix R = MatrixUtils.createRealMatrix(new double[][] {
                { var,    0,   0,    0 },
                {   0, 1e-3,   0,    0 },
                {   0,    0, var,    0 },
                {   0,    0,   0, 1e-3 }
        });

        final ProcessModel pm = new DefaultProcessModel(A, B, Q, initialState, initialErrorCovariance);
        final MeasurementModel mm = new DefaultMeasurementModel(H, R);
        final KalmanFilter filter = new KalmanFilter(pm, mm);

        final List<Number> realX = new ArrayList();
        final List<Number> realY = new ArrayList();
        final List<Number> measuredX = new ArrayList();
        final List<Number> measuredY = new ArrayList();
        final List<Number> kalmanX = new ArrayList();
        final List<Number> kalmanY = new ArrayList();
        
        for (int i = 0; i < iterations; i++) {

            // get real location
            realX.add(cannonball.getX());
            realY.add(cannonball.getY());

            // get measured location
            final double mx = cannonball.getMeasuredX();
            final double my = cannonball.getMeasuredY();

            measuredX.add(mx);
            measuredY.add(my);

            // iterate the cannon simulation to the next timeslice.
            cannonball.step();

            final double[] state = filter.getStateEstimation();
            kalmanX.add(state[0]);
            kalmanY.add(state[2]);

            // update the kalman filter with the measurements
            filter.predict(controlVector);
            filter.correct(new double[] { mx, 0, my, 0 } );
        }

        chart.setXAxisTitle("Distance (m)");
        chart.setYAxisTitle("Height (m)");

        Series dataset = chart.addSeries("true", realX, realY);
        dataset.setMarker(SeriesMarker.NONE);
        
        dataset = chart.addSeries("measured", measuredX, measuredY);
        dataset.setLineStyle(SeriesLineStyle.DOT_DOT);
        dataset.setMarker(SeriesMarker.NONE);

        dataset = chart.addSeries("kalman", kalmanX, kalmanY);
        dataset.setLineColor(Color.red);
        dataset.setLineStyle(SeriesLineStyle.DASH_DASH);
        dataset.setMarker(SeriesMarker.NONE);
    }

    public static Chart createChart(String title, LegendPosition position) {
        Chart chart = new ChartBuilder().width(650).height(450).build();

        // Customize Chart
        chart.setChartTitle(title);
        chart.getStyleManager().setChartTitleVisible(true);
        chart.getStyleManager().setChartTitleFont(new Font("Arial", Font.PLAIN, 12));
        chart.getStyleManager().setLegendPosition(position);
        chart.getStyleManager().setLegendVisible(true);
        chart.getStyleManager().setLegendFont(new Font("Arial", Font.PLAIN, 12));
        chart.getStyleManager().setLegendPadding(6);
        chart.getStyleManager().setLegendSeriesLineLength(10);
        chart.getStyleManager().setAxisTickLabelsFont(new Font("Arial", Font.PLAIN, 10));
        
        chart.getStyleManager().setChartBackgroundColor(Color.white);
        chart.getStyleManager().setChartPadding(4);
        
        chart.getStyleManager().setChartType(ChartType.Line);
        return chart;
    }

    public static JComponent createComponent() {
        JComponent container = new JPanel();
        container.setLayout(new BoxLayout(container, BoxLayout.PAGE_AXIS));

        Chart chart = createChart("Cannonball", LegendPosition.InsideNE);
        cannonballTest(chart);
        container.add(new XChartPanel(chart));
        
        container.setBorder(BorderFactory.createLineBorder(Color.black, 1));
        return container;
    }

    @SuppressWarnings("serial")
    public static class Display extends ExampleFrame {
        
        private JComponent container;

        public Display() {
            setTitle("Commons Math: Kalman Filter - Cannonball");
            setSize(800, 600);
            
            container = new JPanel();
            JComponent comp = createComponent();
            container.add(comp);

            add(container);
        }

        @Override
        public Component getMainPanel() {
            return container;
        }
    }

    public static void main(String[] args) {
        ExampleUtils.showExampleFrame(new Display());
    }
}

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