Angles

Barcode Rotation Angles

When a barcode is rotated in an image, Aspose.BarCode for Java can report its orientation.
This information is exposed through BarCodeRegionParameters for each recognized barcode and can be used for:

  • Understanding how a symbol is oriented on labels or documents
  • Validating layout constraints (for example, barcodes must not be tilted beyond a threshold)
  • Building visual overlays (debug images) with the correct geometry
  • Further image processing that depends on rotation

All examples in this article are based on the sample class:

com.aspose.barcode.guide.recognition.barcode_properties.AnglesExample

You can find the full source code on GitHub:

AnglesExample.java

In the snippets below, variables like imagePath represent paths to sample images that contain rotated barcodes.

1. Reading the Rotation Angle

Each BarCodeResult contains a BarCodeRegionParameters object that describes where the barcode was found.
The method getAngle() returns the approximate rotation angle of the detected barcode in degrees.

String imagePath = "path/to/rotated_code128.png";

BarCodeReader reader = new BarCodeReader(imagePath, DecodeType.CODE_128);
BarCodeResult[] results = reader.readBarCodes();

if (results.length > 0) {
    BarCodeRegionParameters region = results[0].getRegion();
    double angle = region.getAngle();
    System.out.println("Detected angle: " + angle + " degrees");
}

Key points:

  • getAngle() returns a double value in degrees.
  • The angle is estimated by the recognition engine and may differ slightly from the exact rotation.
  • You should compare angles using a tolerance rather than expecting exact equality.

For example, to check if a barcode is approximately 30 degrees rotated:

double angle = region.getAngle();
double expected = 30.0;
double tolerance = 7.5;

boolean isCloseTo30 = Math.abs(angle - expected) <= tolerance;

2. Angles for 2D Barcodes (QR Example)

Angle detection works in the same way for 2D barcodes such as QR codes.
You can combine rotation reading with higher quality settings for more complex images.

String imagePath = "path/to/rotated_qr.png";

BarCodeReader reader = new BarCodeReader(imagePath, DecodeType.QR);
reader.setQualitySettings(QualitySettings.getHighQuality());

BarCodeResult[] results = reader.readBarCodes();

if (results.length > 0) {
    BarCodeRegionParameters region = results[0].getRegion();
    double angle = region.getAngle();
    System.out.println("Detected QR angle: " + angle + " degrees");
}

Key points:

  • The same getAngle() method is used for both 1D and 2D symbologies.
  • QualitySettings.getHighQuality() can improve detection robustness for rotated or small symbols.
  • The reported angle for a QR rotated by about 45 degrees should be close to 45, within a reasonable tolerance.

3. Rectangle vs. Quadrangle for Rotated Barcodes

For each detected barcode, the engine provides two geometric representations of its location:

  • Rectangle – an axis-aligned bounding box.
  • Quadrangle – a four-point shape that follows the actual rotated outline.

You can access both via BarCodeRegionParameters.

String imagePath = "path/to/rotated_code128.png";

BarCodeReader reader = new BarCodeReader(imagePath, DecodeType.CODE_128);
BarCodeResult[] results = reader.readBarCodes();

if (results.length > 0) {
    BarCodeRegionParameters region = results[0].getRegion();

    Rectangle rect = region.getRectangle();
    Quadrangle quad = region.getQuadrangle();

    System.out.println("Rectangle: " + rect);
    System.out.println("Quad LT=" + quad.getLeftTop()
            + " RT=" + quad.getRightTop()
            + " RB=" + quad.getRightBottom()
            + " LB=" + quad.getLeftBottom());

    Rectangle quadBounds = quad.getBoundingRectangle();
    System.out.println("Quadrangle bounds: " + quadBounds);
}

Key points:

  • The Rectangle is always axis-aligned and grows to fully enclose the rotated barcode.
  • The Quadrangle tracks the true corners of the symbol and preserves its rotation and skew.
  • quad.getBoundingRectangle() gives the same axis-aligned bounds as region.getRectangle().

Use the quadrangle when you need precise geometry (for example, drawing the rotated shape),
and use the rectangle when you only need a simple bounding box.

4. Reading Raw Corner Points with getPoints()

If you prefer to work directly with corner points, you can use getPoints() from BarCodeRegionParameters.
It exposes an array of four java.awt.Point objects that correspond to the quadrangle corners.

String imagePath = "path/to/rotated_qr.png";

BarCodeReader reader = new BarCodeReader(imagePath, DecodeType.QR);
reader.setQualitySettings(QualitySettings.getHighQuality());

BarCodeResult[] results = reader.readBarCodes();

if (results.length > 0) {
    BarCodeRegionParameters region = results[0].getRegion();

    Point[] points = region.getPoints();
    if (points != null && points.length == 4) {
        for (int i = 0; i < points.length; i++) {
            System.out.println("Corner " + i + ": " + points[i]);
        }
    }
}

Key points:

  • getPoints() returns four points that describe the corners of the detected region.
  • The order of points is consistent and corresponds to the quadrangle corners.
  • Corner points are useful for custom visualizations and geometry calculations.

5. Drawing a Visual Overlay with Angle and Geometry

The sample class also contains a helper that draws a visual overlay with the rectangle, quadrangle, and detected angle.
This method can be reused in your own applications when you need a debug image to inspect geometry.

private static void drawOverlay(String srcPath, String outPath, BarCodeRegionParameters region) throws Exception {
    BufferedImage img = ImageIO.read(new File(srcPath));
    Graphics2D g = img.createGraphics();
    try {
        g.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);

        Rectangle rect = region.getRectangle();
        g.setColor(new Color(0, 160, 0));
        g.setStroke(new BasicStroke(2f));
        g.drawRect(rect.x, rect.y, rect.width, rect.height);

        Quadrangle q = region.getQuadrangle();
        Point lt = q.getLeftTop();
        Point rt = q.getRightTop();
        Point rb = q.getRightBottom();
        Point lb = q.getLeftBottom();

        g.setColor(new Color(0, 90, 220));
        g.drawLine(lt.x, lt.y, rt.x, rt.y);
        g.drawLine(rt.x, rt.y, rb.x, rb.y);
        g.drawLine(rb.x, rb.y, lb.x, lb.y);
        g.drawLine(lb.x, lb.y, lt.x, lt.y);

        String text = String.format("angle: %.1f°", region.getAngle());
        g.setColor(Color.BLACK);
        g.drawString(text, Math.max(0, rect.x), Math.max(12, rect.y - 6));
    } finally {
        g.dispose();
    }
    ImageIO.write(img, "PNG", new File(outPath));
    System.out.println("[INFO] Overlay saved: " + outPath);
}

Key points:

  • Draws the axis-aligned rectangle and the quadrangle in different colors.
  • Annotates the image with the detected angle value.
  • Uses anti-aliasing for smoother lines.
  • Saves the overlay as a PNG image that can be inspected manually.

Summary

Aspose.BarCode for Java provides detailed rotation information for each recognized barcode:

  • BarCodeRegionParameters.getAngle() returns the approximate angle in degrees.
  • getRectangle() gives an axis-aligned bounding box.
  • getQuadrangle() and getPoints() provide precise corner geometry for rotated symbols.
  • You can combine these APIs to validate orientation, enforce layout rules, or draw visual overlays.

All examples shown here are based on:

AnglesExample.java

Use these patterns as a reference when working with barcode rotation angles in your own Java applications.

Coordinates