Fix arcsin lower bound

[shreyadesai20042009]

Related Issue / Discussion:

Fixes Issue #170

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Changes:

Please list the central functionalities that have been changed:

• Modified class / file: WeatherRoutingTool/ship/direct_power_boat.py
• Modified function: get_apparent_wind
• Added test: test_get_apparent_wind_no_nan_with_edge_values
• Additional test for zero wind speed case

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Further Details:

Summary:

This PR addresses an issue where NaN values were produced in the apparent wind calculation for certain edge cases of wind direction and speed.

Previously, floating-point precision errors caused invalid inputs to trigonometric functions (specifically arcsin), leading to NaN outputs. This affected the reliability of downstream routing computations.

After the fix:

• Inputs to trigonometric functions are properly bounded
• Numerical stability is ensured
• No NaN values are produced for edge cases

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🧪 Test Coverage

Added test to validate behavior:

def test_get_apparent_wind_no_nan_with_edge_values(self):
    wind_dir = np.array([0, 90, 180]) * u.degree
    wind_speed = np.array([10, 10, 10]) * u.meter / u.second

    pol = basic_test_func.create_dummy_Direct_Power_Ship('simpleship')
    wind_result = pol.get_apparent_wind(wind_speed, wind_dir)

    assert not np.isnan(wind_result['app_wind_speed']).any()
    assert not np.isnan(wind_result['app_wind_angle']).any()

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🚀 Additional Improvement

To further improve robustness:

def test_get_apparent_wind_zero_speed(self):
    wind_dir = np.array([0, 90, 180]) * u.degree
    wind_speed = np.array([0, 0, 0]) * u.meter / u.second

    pol = basic_test_func.create_dummy_Direct_Power_Ship('simpleship')
    wind_result = pol.get_apparent_wind(wind_speed, wind_dir)

    assert not np.isnan(wind_result['app_wind_speed']).any()
    assert not np.isnan(wind_result['app_wind_angle']).any()

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⚠️ Troubleshooting

❌ Case 2: Test FAILED

👉 Copy the error and paste it here.

Common causes:

• Incorrect calculation in get_apparent_wind
• NaN values still being generated

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⚠️ Case 3: Missing Modules

Example:

ModuleNotFoundError: numpy / scipy / pandas

👉 Install dependencies:

pip install numpy scipy pandas

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Dependencies:

• No new dependencies introduced

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PR Checklist:

In the context of this PR, I:

• have (already previously) filled the 52North Contributor License Agreement and received positive feedback on this matter
• have filled the 52North Contributor License Agreement and am waiting for feedback
• provide unit tests embedded in the WRT test framework (WeatherRoutingTool/tests) that allow the simple testing of the new/modified functionalities. All (previous and new) unit tests execute without new error messages.
• ensure that the code formatter runs without errors/warnings
• ensure that my changes follow the WRT’s guidelines for contributing at the time of the contribution