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@@ -2,7 +2,8 @@ | |
| | File: imu.py | ||
| | Author: Marcelo Jacinto ([email protected]) | ||
| | License: BSD-3-Clause. Copyright (c) 2023, Marcelo Jacinto. All rights reserved. | ||
| | Description: Simulates an imu. Based on the implementation provided in PX4 stil_gazebo (https://github.com/PX4/PX4-SITL_gazebo) | ||
| | Description: Simulates an imu. Based on the implementation provided in PX4 stil_gazebo | ||
| (https://github.com/PX4/PX4-SITL_gazebo) | ||
| """ | ||
| __all__ = ["IMU"] | ||
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@@ -18,11 +19,12 @@ | |
| class IMU(Sensor): | ||
| """The class that implements the IMU sensor. This class inherits the base class Sensor. | ||
| """ | ||
| def __init__(self, config={}): | ||
| def __init__(self, config=None): | ||
| """Initialize the IMU class | ||
| Args: | ||
| config (dict): A Dictionary that contains all teh parameters for configuring the IMU - it can be empty or only have some of the parameters used by the IMU. | ||
| config (dict): A Dictionary that contains all teh parameters for configuring the IMU - it can be empty or | ||
| only have some of the parameters used by the IMU. | ||
| Examples: | ||
| The dictionary default parameters are | ||
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@@ -82,12 +84,13 @@ def state(self): | |
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| @Sensor.update_at_rate | ||
| def update(self, state: State, dt: float): | ||
| """Method that implements the logic of an IMU. In this method we start by generating the random walk of the | ||
| gyroscope. This value is then added to the real angular velocity of the vehicle (FLU relative to ENU inertial frame | ||
| expressed in FLU body frame). The same logic is followed for the accelerometer and the accelerations. After this step, | ||
| the angular velocity is rotated such that it expressed a FRD body frame, relative to a NED inertial frame, expressed | ||
| in the FRD body frame. Additionally, the acceleration is also rotated, such that it becomes expressed in the body | ||
| FRD frame of the vehicle. This sensor outputs data that follows the PX4 adopted standard. | ||
| """Method that implements the logic of an IMU. In this method we start by generating the random walk of the | ||
| gyroscope. This value is then added to the real angular velocity of the vehicle (FLU relative to ENU inertial | ||
| frame expressed in FLU body frame). The same logic is followed for the accelerometer and the accelerations. | ||
| After this step, the angular velocity is rotated such that it expressed a FRD body frame, relative to a NED | ||
| inertial frame, expressed in the FRD body frame. Additionally, the acceleration is also rotated, such that it | ||
| becomes expressed in the body FRD frame of the vehicle. This sensor outputs data that follows the PX4 adopted | ||
| standard. | ||
| Args: | ||
| state (State): The current state of the vehicle. | ||
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@@ -117,10 +120,10 @@ def update(self, state: State, dt: float): | |
| self._gyroscope_bias[i] = phi_g_d * self._gyroscope_bias[i] + sigma_b_g_d * np.random.randn() | ||
| angular_velocity[i] = state.angular_velocity[i] + sigma_g_d * np.random.randn() + self._gyroscope_bias[i] | ||
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| # Accelerometer terms | ||
| # Accelerometer terms. | ||
| tau_a: float = self._accelerometer_bias_correlation_time | ||
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| # Discrete-time standard deviation equivalent to an "integrating" sampler with integration time dt | ||
| # Discrete-time standard deviation equivalent to an "integrating" sampler with integration time dt. | ||
| sigma_a_d: float = 1.0 / np.sqrt(dt) * self._accelerometer_noise_density | ||
| sigma_b_a: float = self._accelerometer_random_walk | ||
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@@ -130,14 +133,16 @@ def update(self, state: State, dt: float): | |
| # Compute state-transition. | ||
| phi_a_d: float = np.exp(-1.0 / tau_a * dt) | ||
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| # Compute the linear acceleration from diferentiating the velocity of the vehicle expressed in the inertial frame | ||
| # Compute the linear acceleration from diferentiating the velocity of the vehicle expressed in the inertial | ||
| # frame. | ||
| linear_acceleration_inertial = (state.linear_velocity - self._prev_linear_velocity) / dt | ||
| linear_acceleration_inertial = linear_acceleration_inertial - GRAVITY_VECTOR | ||
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| # Update the previous linear velocity for the next computation | ||
| self._prev_linear_velocity = state.linear_velocity | ||
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| # Compute the linear acceleration of the body frame, with respect to the inertial frame, expressed in the body frame | ||
| # Compute the linear acceleration of the body frame, with respect to the inertial frame, expressed in the body | ||
| # frame. | ||
| linear_acceleration = np.array(Rotation.from_quat(state.attitude).inv().apply(linear_acceleration_inertial)) | ||
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| # Simulate the accelerometer noise processes and add them to the true linear aceleration values | ||
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