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graphing a polygon with double values

Posted on 2006-11-20
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Last Modified: 2008-02-01
I'm looking to generate plotted Point graph output using a graphic library that creates a 2D set of cartesian axes, plots points[i] for i = 0 to points.length-1. Also draws lines between each of points[n] and points[n+1] for n = 0 to points.length-2. Also plot a line from points[points.length-1] to points[0].

Here is my code but it doesn't work....please help!


import java.lang.Math.*;
import java.awt.*;
import java.awt.geom.*;
import java.awt.Polygon;
import java.awt.Graphics;

/* more code above but not necessary to show i don't think */

public void draw ( Point[] points, String[] text )
            {
                  x = new long[points.length];
                  y = new long[points.length];
                  tempPoint = new Point[points.length];
                  Graphics g1 = null;


                  for (int i = 0; i < points.length; i++)
                  {
                        x[i] = points[i].x();
                        y[i] = points[i].y();
                        tempPoint[i] = new Point(x[i], y[i]);
                  }

                  LongPolygon g = new LongPolygon(tempPoint);



                  g1.drawPolygon(g);
                  System.out.println(text);
            }      

private class LongPolygon extends Polygon
      {
            private Point[] tempPoints;

            public LongPolygon(Point[] points)
            {
                  tempPoints =  points;
            }
      }            
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Question by:shpark82
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ADSLMark earned 2000 total points
ID: 17987233
I have no idea what you want to do, but here is some example code.

--PolygonExample.java
import java.awt.*;
import java.awt.geom.*;
import javax.swing.*;

class PolygonExample extends JFrame
{
    final static int NUM_POINTS = 10;

    //Constructor
    public PolygonExample()
    {
        //Set frame properties
        this.setSize(800, 600);
        this.setTitle("Polygon Example");
        this.setLayout(null);
        this.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

        //Fille list with some random points
        Point2D.Double[] points = new Point2D.Double[NUM_POINTS];
        for(int i=0;i<NUM_POINTS;i++)
        {
            double r1 = (Math.random()*20) - 10;
            double r2 = (Math.random()*20) - 10;
            points[i] = new Point2D.Double(r1, r2);
        }

        PolygonGraph pg = new PolygonGraph(points);
        pg.setBounds(200, 100, 400, 400);
        this.add(pg);
    }

    //Program entry
    public static void main(String[] args)
    {
        PolygonExample pe = new PolygonExample();
        pe.setVisible(true);
    }
}

--PolygonGraph.java
import java.awt.*;
import java.awt.geom.*;
import javax.swing.*;

class PolygonGraph extends JPanel
{
    private Point2D.Double[] points;

    //Screen points/sizes
    final static int GRAPH_WIDTH = 400-1;
    final static int GRAPH_HEIGHT = 400-1;

    final static int GRAPH_ORIGIN_X = GRAPH_WIDTH/2;
    final static int GRAPH_ORIGIN_Y = GRAPH_HEIGHT/2;

    //Real points/sizes
    final static double MIN_X = -10.0;
    final static double MAX_X = 10.0;

    final static double MIN_Y = -10.0;
    final static double MAX_Y = 10.0;

    final static double STEP_SIZE_X = 1.0;
    final static double STEP_SIZE_Y = 1.0;

    //Constructor
    public PolygonGraph(Point2D.Double[] points)
    {
        this.setSize(GRAPH_WIDTH, GRAPH_HEIGHT);

        this.points = points;
    }

    //Override paintcomponent
    public void paintComponent(Graphics g)
    {
        super.paintComponent(g);

        this.draw((Graphics2D) g);
    }

    //Draw graph
    public void draw(Graphics2D g2)
    {
        this.drawGrid(g2);
        this.drawPolygon(g2);
    }

    //Draw polygon
    public void drawPolygon(Graphics2D g2)
    {
        //Set graphics properties
        g2.setColor(Color.BLUE);

        //Split points
        int[] xPoints = new int[points.length];
        int[] yPoints = new int[points.length];

        //Create point lists
        for(int i=0;i<points.length;i++)
        {
            Point p = realToScreen(points[i]);
            xPoints[i] = (int) p.getX();
            yPoints[i] = (int) p.getY();
        }

        //Draw polygon
        g2.drawPolygon(xPoints, yPoints, points.length);
    }

    //Draw grid
    public void drawGrid(Graphics2D g2)
    {
        Point p1; Point p2;
        double gridX; double gridY;

        //Draw vertical lines

        //To the right
        g2.setColor(Color.LIGHT_GRAY);
        g2.setStroke(new BasicStroke(1));
        gridX = 0;
        while(gridX<MAX_X)
        {
            gridX += STEP_SIZE_X;

            p1 = realToScreen(new Point2D.Double(gridX, MAX_Y));
            p2 = realToScreen(new Point2D.Double(gridX, MIN_Y));
            g2.drawLine((int) p1.getX(), (int) p1.getY(), (int) p2.getX(), (int) p2.getY());
        }

        //Center line
        g2.setColor(Color.BLACK);
        g2.setStroke(new BasicStroke(2));
        p1 = realToScreen(new Point2D.Double(0, MAX_Y));
        p2 = realToScreen(new Point2D.Double(0, MIN_Y));
        g2.drawLine((int) p1.getX(), (int) p1.getY(), (int) p2.getX(), (int) p2.getY());

        //To the left
        g2.setColor(Color.LIGHT_GRAY);
        g2.setStroke(new BasicStroke(1));
        gridX = 0;
        while(gridX>MIN_X)
        {
            gridX -= STEP_SIZE_X;

            p1 = realToScreen(new Point2D.Double(gridX, MAX_Y));
            p2 = realToScreen(new Point2D.Double(gridX, MIN_Y));
            g2.drawLine((int) p1.getX(), (int) p1.getY(), (int) p2.getX(), (int) p2.getY());
        }

        //Draw horizontal lines

        //To the top
        g2.setColor(Color.LIGHT_GRAY);
        g2.setStroke(new BasicStroke(1));
        gridY = 0;
        while(gridY<MAX_Y)
        {
            gridY += STEP_SIZE_Y;

            p1 = realToScreen(new Point2D.Double(MAX_X, gridY));
            p2 = realToScreen(new Point2D.Double(MIN_X, gridY));
            g2.drawLine((int) p1.getX(), (int) p1.getY(), (int) p2.getX(), (int) p2.getY());
        }

        //Center line
        g2.setColor(Color.BLACK);
        g2.setStroke(new BasicStroke(2));
        p1 = realToScreen(new Point2D.Double(MAX_X, 0));
        p2 = realToScreen(new Point2D.Double(MIN_X, 0));
        g2.drawLine((int) p1.getX(), (int) p1.getY(), (int) p2.getX(), (int) p2.getY());

        //To the bottom
        g2.setColor(Color.LIGHT_GRAY);
        g2.setStroke(new BasicStroke(1));
        gridY = 0;
        while(gridY>MIN_Y)
        {
            gridY -= STEP_SIZE_Y;

            p1 = realToScreen(new Point2D.Double(MAX_X, gridY));
            p2 = realToScreen(new Point2D.Double(MIN_X, gridY));
            g2.drawLine((int) p1.getX(), (int) p1.getY(), (int) p2.getX(), (int) p2.getY());
        }
    }

    //Convert point from real to screen
    public static Point realToScreen(Point2D.Double p)
    {
        double scaleXFactor = GRAPH_WIDTH  / (MAX_X-MIN_X);
        double scaleYFactor = GRAPH_HEIGHT / (MAX_Y-MIN_Y);

        double translateXFactor = -MIN_X;
        double translateYFactor = -MIN_Y;

        return new Point((int) Math.floor((p.getX()+translateXFactor)*scaleXFactor)
                        ,(int) Math.floor((p.getY()+translateYFactor)*scaleYFactor));
    }
}

I hope it works, I didn't test it thorougly. You should see it as a step in the right direction, you probably have to adjust quite a lot to fit your needs, but the design is flexible.

Good luck.
Mark
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