Polar equation of a line between two points

Question

I am trying to make a method to output the points (in polar coordinates (r, theta)) along a line between two given polar coordinates.
This will mimick the path of an object traveling across a radar screen.
Is this possible?

Answer 1

Java does not plot in polar coordiantes, you'll have to convert to rectangular to get a plot. If you're just doing a sweep on a screen, then it's fairly simple to do:
r is the radius of your screen,
(0,0) is your Origin translated as (Xmax/2, Ymax/2)
when you draw the line you just start at your Origin and get your end values as
X1=X0+r*cos(Theta) and
Y1=Y0+r*sin(Theta),
I've not seen, nor do I think there is any other support to do what you want--you have to convert to (x,y) coordinate system.
This will leave a ragged edge so make a border around your screen.
import java.awt.Color;
import java.awt.Dimension;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.awt.Point;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;
public class JRadar{
  public JRadar(){
    JPanel p = new MyJPanel();
    JFrame f = new JFrame("ForumJunk: JRadar");
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    f.add(p);
    f.pack();
    f.setVisible(true);
  public static void main(String[] args){
    new JRadar();
  class MyJPanel extends JPanel implements ActionListener{
    Timer t = new Timer(10, this);
    Dimension d = new Dimension(512, 512);
    BufferedImage bi = new BufferedImage(d.width, d.height, BufferedImage.TYPE_INT_RGB);
    Graphics2D g = bi.createGraphics();
    double theta = 0;
    int r = d.width/2 - 16;
    Point origin = new Point(d.width/2, d.height/2);
    public MyJPanel(){
      g.setColor(Color.RED);
      this.setPreferredSize(d);
      t.start();
    public void actionPerformed(ActionEvent e){
      g.clearRect(0, 0, d.width, d.height);
      g.drawOval(16, 16, 480, 480);
      g.drawLine(origin.x, origin.y, (int)(origin.x+r*Math.cos(theta)), (int)(origin.y+r*Math.sin(theta)));
      theta += 0.01;
      if(theta>=Math.PI*2) theta = 0.0;
      repaint();
    public void paintComponent(Graphics g){
      super.paintComponent(g);
      g.drawImage(bi, 0, 0, this);
}Edited by: morgalr on Mar 3, 2010 4:59 PM: code example added