Troubleshooting Rotation Function Failure In Test 3

Nov 29, 2025 by Alex Johnson 52 views

This article dives into a specific issue encountered while applying a rotation function, particularly the failure observed during Test 3. We'll analyze the provided C++ code snippet, pinpoint potential causes for the failure, and discuss strategies for debugging and resolving the problem. Whether you're a seasoned programmer or just starting out, understanding how to approach such challenges is crucial for software development success.

Understanding the Code

Let's begin by examining the C++ code responsible for applying the rotation:

Minutia apply_rotation(const Minutia &minutia, int center_row, int center_column, int rotation_in_degrees) {
    // initialisation des coordonnées et de l'orientation de la minutie
    int row = minutia.row;
    int col = minutia.column;
    int orientation = minutia.angle_in_degrees;
    double rotation = degrees_to_radians(rotation_in_degrees);
    cout << row <<" "<< col <<" "<< orientation << " "<< rotation;
    // calcul des variables temporaires relativement a l'énoncé
    int x = col - center_column;
    int y = center_row - row;
    int newx = (x*cos(rotation)) - (y*sin(rotation));
    int newy = (y*cos(rotation)) + (x*sin(rotation));

    int newrow = static_cast<int>(round(center_row - newy));
    int newcol = static_cast<int>(round(newx + center_column));
    int new_orientation = static_cast <int> ((orientation + rotation_in_degrees)%360);
    //retour de la minutie nouvellement orientée
    Minutia newMinutia ({newrow , newcol , new_orientation});
    return newMinutia;
}

This function, apply_rotation, takes a Minutia object (presumably representing a point or feature), the center of rotation coordinates (center_row, center_column), and the rotation angle in degrees (rotation_in_degrees) as input. It then calculates the new coordinates and orientation of the minutia after the rotation and returns a new Minutia object.

Key Steps in the Function:

Initialization: The function starts by extracting the row, column, and orientation from the input minutia object.
Degrees to Radians Conversion: The rotation angle, initially in degrees, is converted to radians using the degrees_to_radians function (not shown in the snippet, but presumably defined elsewhere).
Coordinate Transformation: The core of the rotation logic lies in these lines:
```
int x = col - center_column;
int y = center_row - row;
int newx = (x*cos(rotation)) - (y*sin(rotation));
int newy = (y*cos(rotation)) + (x*sin(rotation));
```
These calculations perform the standard 2D rotation transformation around the given center point. The original coordinates are first translated relative to the center, then rotated using trigonometric functions, and finally translated back to the original coordinate system.
New Coordinates and Orientation: The rotated coordinates (newx, newy) are then used to calculate the new row and column (newrow, newcol) for the minutia. The new orientation is calculated by adding the rotation angle to the original orientation and taking the modulo 360 to keep the angle within the range of 0 to 359 degrees.
Minutia Object Creation and Return: Finally, a new Minutia object is created with the calculated row, column, and orientation, and returned.

Potential Causes of Failure in Test 3

Now, let's delve into the possible reasons why Test 3 might be failing. Since the code appears to implement the rotation logic correctly at first glance, the issue might lie in subtle details or edge cases.

Floating-Point Precision: The rotation calculations involve trigonometric functions (cos and sin) and floating-point arithmetic. Floating-point numbers have limited precision, which can lead to rounding errors. These errors, even if small, can accumulate over multiple calculations and cause the final result to deviate significantly from the expected value. This is especially relevant when dealing with angles close to multiples of 90 degrees, where trigonometric functions can be more sensitive to small errors. It's crucial to use round function to ensure the conversion from floating point to integer is done correctly.
Integer Overflow: Although less likely, integer overflow is a potential concern. If the rotated coordinates (newx, newy) or the final row and column values (newrow, newcol) become too large or too small to be represented by an int, overflow can occur, leading to unexpected results. This is more probable if the input coordinates or the rotation center are far from the origin.
Incorrect Center of Rotation: A common mistake is to provide an incorrect center of rotation. If the center_row and center_column values are not the intended center point, the rotation will be performed around the wrong location, resulting in incorrect output. Double-check the values used for the center of rotation in Test 3.
Test Case Specific Issues: The failure might be specific to the test case used in Test 3. This could involve edge cases, boundary conditions, or specific input values that expose a flaw in the rotation logic or its interaction with other parts of the system. For instance, Test 3 might be using a very large rotation angle, a point close to the rotation center, or a combination of factors that trigger the failure.
degrees_to_radians Function: While not explicitly shown, the degrees_to_radians function is critical for accurate rotation. If this function is implemented incorrectly, the rotation calculations will be based on the wrong angle, leading to incorrect results. Verify the implementation of degrees_to_radians to ensure it correctly converts degrees to radians.
Modulo Operator and Orientation Calculation: The modulo operator (%) is used to ensure the new orientation remains within the range of 0 to 359 degrees. However, if the orientation + rotation_in_degrees sum is negative, the result of the modulo operation might also be negative in some programming languages. Ensure the modulo operation handles negative values correctly.
Minutia Data Structure: There might be an issue with the Minutia data structure itself. If the row, column, or angle_in_degrees members are not of the expected type or range, it could lead to data corruption or incorrect calculations. Inspect the definition of the Minutia struct to ensure it's defined correctly.

Debugging Strategies

To pinpoint the exact cause of the failure in Test 3, a systematic debugging approach is essential. Here are several strategies you can employ:

Print Statements: The code snippet already includes cout statements to print the initial row, column, orientation, and rotation values. Expand on this by adding more print statements at various points in the function to track the values of intermediate variables such as x, y, newx, newy, newrow, and newcol. This will help you trace the flow of execution and identify where the calculations deviate from the expected values.
Unit Tests: Create a series of unit tests that specifically target the apply_rotation function. These tests should cover a range of input values, including edge cases, boundary conditions, and angles close to multiples of 90 degrees. Comparing the actual output of the function with the expected output for each test case will help isolate the problem.
Debugging Tools: Utilize a debugger to step through the code line by line, inspect variable values, and identify the exact point where the failure occurs. This can be particularly useful for complex calculations or when dealing with floating-point precision issues.
Simplified Test Cases: If Test 3 involves a complex scenario, try creating a simplified test case that isolates the rotation logic. This will make it easier to understand the behavior of the function and identify the root cause of the problem.
Visualizations: For geometric transformations like rotations, visualizing the results can be extremely helpful. You can plot the original minutia, the rotation center, and the rotated minutia on a graph or diagram to visually verify the correctness of the rotation.
Code Review: Have a colleague review your code. A fresh pair of eyes can often spot errors or assumptions that you might have missed.

Example Debugging Scenario

Let's illustrate a debugging scenario with a potential cause: floating-point precision. Suppose Test 3 uses a rotation angle of 90 degrees and the output newrow is slightly off from the expected integer value due to rounding errors. You could add the following print statements to your code:

int newx = (x*cos(rotation)) - (y*sin(rotation));
int newy = (y*cos(rotation)) + (x*sin(rotation));
cout << "newx: " << newx << ", newy: " << newy << endl;

int newrow = static_cast<int>(round(center_row - newy));
int newcol = static_cast<int>(round(newx + center_column));
cout << "center_row - newy: " << center_row - newy << endl; // Added print statement
cout << "newrow: " << newrow << endl;

By examining the output, you might observe that center_row - newy is a floating-point number very close to an integer, but not exactly equal. The round function then correctly rounds it to the nearest integer, but the small discrepancy might still cause the test to fail if it expects an exact integer match.

In this case, you might consider using a tolerance value when comparing the expected and actual results in your test case, or adjusting the calculation to minimize floating-point errors.

Conclusion

Troubleshooting failures in software development is a crucial skill. By understanding the code, identifying potential causes, and employing systematic debugging strategies, you can effectively resolve issues and build robust applications. The failure in Test 3 for the apply_rotation function likely stems from a combination of factors, including floating-point precision, incorrect input values, or edge case scenarios. By using print statements, unit tests, and debugging tools, you can pinpoint the exact cause and implement the necessary fixes.

Remember to pay close attention to the details, test your code thoroughly, and don't hesitate to seek help from colleagues or online resources. Debugging can be challenging, but it's also a rewarding process that leads to a deeper understanding of your code and the underlying principles of software engineering.

For further reading on rotation transformations and debugging techniques, you can check out resources like the Wikipedia article on Rotation Matrix.