How to Correctly Plot Data and Text on a Rotated Coordinate Plane in Java?

Rotating Coordinate Plane for Data and Text in Java: Resolving Plotting Issues

In Java, rotating a coordinate plane and plotting data and labels correctly requires addressing several key issues. This article provides a solution to two common problems:

1. Plotting data points with the upper left corner as the origin and y-values descending downward
2. Failing to draw labels for tic marks on the y-axis

Solution Overview

To fix these issues, the provided code has been modified as follows:

1. DataPanel.java

<code class="java">import java.awt.*;
import java.awt.geom.AffineTransform;
import javax.swing.*;
import java.text.DecimalFormat;
import java.text.NumberFormat;
import java.util.*;

class DataPanel extends JPanel {
    // ...

    @Override
    protected void paintComponent(Graphics g) {// Override paintComponent() method.
        super.paintComponent(g);
        // ...
        // Invert the y-axis.
        AffineTransform at = g2d.getTransform();//save the graphics context's transform
        g2d.translate(leftStartPlotWindow, blueTop);//translate origin to bottom-left corner of blue rectangle
        g2d.scale(1, -1);//invert the y-axis
        // ...
        // Restore the transform for conventional rendering.
        g2d.setTransform(at);//restore the transform for conventional rendering
        // ...
    }

    // ...
}</code>

2. DataGUI.java

No changes are required in this file.

Explanation

• The key to rotating the coordinate plane is using AffineTransform. The graphics context is transformed by translating the origin to the bottom-left corner of the blue rectangle and then scaling the y-axis by -1, effectively inverting it.
• Once the transformation is applied, the data points and labels can be plotted using cartesian coordinates.
• After plotting is complete, the original transform is restored to revert to conventional rendering for the x-axis label and other components.
• As a result, the data points are now plotted from the bottom-left corner upward, and the y-axis labels are correctly displayed and rotated.

Additional Resources

• [AffineTransform](https://docs.oracle.com/javase/8/docs/api/java/awt/geom/AffineTransform.html)

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