# Source code for stonesoup.movable.movable

```
import datetime
from abc import abstractmethod, ABC
from functools import lru_cache
from typing import Sequence, Tuple, MutableSequence, Optional
import numpy as np
from math import cos, sin
from scipy.linalg import expm
from stonesoup.base import Property
from stonesoup.functions import cart2sphere, cart2pol, build_rotation_matrix, rotz
from stonesoup.models.transition import TransitionModel
from stonesoup.types.array import StateVector
from stonesoup.types.state import State, StateMutableSequence
from stonesoup.sensormanager.action import Actionable
[docs]
class Movable(StateMutableSequence, Actionable, ABC):
states: MutableSequence[State] = Property(
doc="A list of States which enables the platform's history to be "
"accessed in simulators and for plotting. Initiated as a "
"state, for a static platform, this would usually contain its "
"position coordinates in the form ``[x, y, z]``. For a moving "
"platform it would contain position and velocity interleaved: "
"``[x, vx, y, vy, z, vz]``")
position_mapping: Sequence[int] = Property(
doc="Mapping between platform position and state vector. For a "
"position-only 3d platform this might be ``[0, 1, 2]``. For a "
"position and velocity platform: ``[0, 2, 4]``")
velocity_mapping: Optional[Sequence[int]] = Property(
default=None,
doc="Mapping between platform velocity and state dims. If not "
"set, it will default to ``[m+1 for m in position_mapping]``")
# TODO: Determine where a platform coordinate frame should be maintained
def __init__(self, *args, **kwargs):
"""
Ensure that the platform location and the sensor locations are
consistent at initialisation.
"""
super().__init__(*args, **kwargs)
# Set values to defaults if not provided
if self.velocity_mapping is None:
self.velocity_mapping = [p + 1 for p in self.position_mapping]
if not self.states:
raise ValueError('States must not be empty: it must contain least one state.')
@property
def position(self) -> StateVector:
"""Return the position of the platform.
Extracted from the state vector of the platform using the platform's
:attr:`position_mapping`. This property is settable for fixed platforms, but not for
movable ones, where the position must be set by moving the model with a transition model.
"""
return self.state_vector[self.position_mapping, :]
@position.setter
def position(self, value: StateVector) -> None:
self._set_position(value)
@property
def ndim(self) -> int:
"""Convenience property to return the number of dimensions in which the platform operates.
Given by the length of the :attr:`position_mapping`
"""
return len(self.position_mapping)
@property
@abstractmethod
def orientation(self) -> StateVector:
"""Return the orientation of the platform.
Implementation is case dependent and left to the Fixed/Moving subclasses
"""
raise NotImplementedError
@property
@abstractmethod
def velocity(self) -> StateVector:
"""Return the velocity of the platform.
Implementation is case dependent and left to the Fixed/Moving subclasses
"""
raise NotImplementedError
@property
@abstractmethod
def is_moving(self) -> bool:
"""Return the ``True`` if the platform is moving, ``False`` otherwise.
"""
raise NotImplementedError
[docs]
@abstractmethod
def move(self, timestamp: datetime.datetime, noise: bool = True, **kwargs) -> None:
"""Update the platform position using the :attr:`transition_model`.
Parameters
----------
timestamp: :class:`datetime.datetime`
A timestamp signifying when the end of the maneuver
Notes
-----
This methods updates the value of :attr:`position`.
Any provided ``kwargs`` are forwarded to the :attr:`transition_model`.
If :attr:`transition_model` or ``timestamp`` is ``None``, the method has
no effect, but will return successfully.
"""
raise NotImplementedError
@abstractmethod
def _set_position(self, value: StateVector) -> None:
raise NotImplementedError
def _get_rotated_offset(self, offset: StateVector) -> np.ndarray:
""" Determine the sensor mounting offset for the platforms relative
orientation.
Parameters
----------
offset : :class:`~.StateVector`
Mounting offset to rotate
Returns
-------
: :class:`np.ndarray`
Sensor mounting offset rotated relative to platform motion
"""
if self.is_moving:
vel = self.velocity
rot = _get_rotation_matrix(vel)
return rot @ offset
else:
return offset
[docs]
def range_and_angles_to_other(self, other: 'Movable') -> Tuple[float, float, float]:
""" Calculate the range, azimuth and elevation of a given Movable relative to current
Movable.
Calculates the relative vector between the two Movables, and then converts this
range, azimuth, elevation using :func:`.cart2sphere`
Parameters
----------
other : :class:`~.Movable`
Another Movable. Only its position is relevant to this method.
Returns
-------
range, azimuth, elevation : :class:`float`, :class:`float`, :class:`float`
The range azimuth and elevation of the target from the radar
"""
# state relative to radar (in cartesian space)
relative_vector = other.position - self.position
relative_vector = self._rotation_matrix @ relative_vector
# calculate target position in spherical coordinates
[range_, azimuth, elevation] = cart2sphere(*relative_vector)
return range_, azimuth, elevation
@property
def _rotation_matrix(self) -> np.ndarray:
"""_rotation_matrix getter method
Calculates and returns the (3D) axis rotation matrix.
Returns
-------
: :class:`~numpy.ndarray` of shape (3, 3)
The model (3D) rotation matrix.
"""
return build_rotation_matrix(self.orientation)
[docs]
class FixedMovable(Movable):
"""Fixed platform base class
A platform represents a random object defined as a :class:`~.StateMutableSequence`
with fixed (but settable) position and orientation.
.. note:: Position and orientation are read/write properties in this class.
"""
orientation: StateVector = Property(
default=None,
doc='A fixed orientation of the static platform. Defaults to the zero vector')
def __init__(self, *args, **kwargs):
velocity_mapping = kwargs.get('velocity_mapping', None)
if velocity_mapping:
raise ValueError('Velocity mapping should not be set for a FixedMovable')
super().__init__(*args, **kwargs)
self.velocity_mapping = None
if self.orientation is None:
self.orientation = StateVector([0, 0, 0])
def _set_position(self, value: StateVector) -> None:
self.state_vector[self.position_mapping, :] = value
@property
def velocity(self) -> StateVector:
"""Return the velocity of the platform.
For a fixed platform this is always a zero vector of length :attr:`ndim`.
"""
return StateVector([0] * self.ndim)
@property
def is_moving(self) -> bool:
return False
[docs]
def move(self, timestamp: datetime.datetime, **kwargs) -> None:
"""For a fixed platform this method has no effect other than to update the timestamp."""
new_state = State.from_state(self.state, timestamp=timestamp)
self.states.append(new_state)
[docs]
class MovingMovable(Movable):
"""Moving platform base class
A platform represents a random object defined as a :class:`~.State`
that moves according to a given :class:`~.TransitionModel`.
.. note:: Position and orientation are a read only properties in this class.
"""
transition_model: TransitionModel = Property(doc="Transition model")
@property
def velocity(self) -> StateVector:
"""Return the velocity of the platform.
Extracted from the state vector of the platform using the platform's
:attr:`velocity_mapping`. If the state vector is too short and does not contain the
elements specified in the :attr:`velocity_mapping` this raises an :class:`AttributeError`
"""
try:
return self.state_vector[self.velocity_mapping, :]
except IndexError:
raise AttributeError('Velocity is not defined for this platform')
@property
def orientation(self) -> StateVector:
"""Return the orientation of the platform.
This is defined as a 3x1 StateVector of angles (rad), specifying the sensor orientation in
terms of the counter-clockwise rotation around each Cartesian axis in the order
:math:`x,y,z`. The rotation angles are positive if the rotation is in the counter-clockwise
direction when viewed by an observer looking along the respective rotation axis,
towards the origin.
The orientation of this platform is defined as along the direction of its velocity, with
roll always set to zero (as this is the angle the platform is rotated about the velocity
axis, which is not defined in this approximation).
Notes
-----
A non-moving platform (``self.is_moving == False``) does not have a defined orientation in
this approximations and so raises an :class:`AttributeError`
"""
if not self.is_moving:
raise AttributeError('Orientation of a zero-velocity moving platform is not defined')
velocity = self.velocity
if self.ndim == 3:
_, bearing, elevation = cart2sphere(*velocity.flat)
return StateVector([0, elevation, bearing])
elif self.ndim == 2:
_, bearing = cart2pol(*velocity.flat)
return StateVector([0, 0, bearing])
else:
raise NotImplementedError('Orientation of a moving platform is only implemented for 2'
'and 3 dimensions')
@property
def is_moving(self) -> bool:
"""Return the ``True`` if the platform is moving, ``False`` otherwise.
Equivalent (for this class) to ``all(v == 0 for v in self.velocity)``
"""
# Note: a platform without a transition model can be given a velocity as part of it's
# StateVector. It just won't move
# This inconsistency is handled in the move logic
return np.any(self.velocity != 0)
def _set_position(self, value: StateVector):
# The logic below is this: if a moving platform is being built from (say) input
# real-world data then its transition model would not be set, and so it would be fine to
# set its position. However, if the transition model is set, then setting the position is
# both unexpected and may cause odd effects, so is forbidden
if self.transition_model is None:
self.state_vector[self.position_mapping, :] = value
else:
raise AttributeError('Cannot set the position of a moving platform with a '
'transition model')
[docs]
def move(self, timestamp=None, noise=True, **kwargs) -> None:
"""Propagate the platform position using the :attr:`transition_model`.
Parameters
----------
timestamp: :class:`datetime.datetime`, optional
A timestamp signifying when the end of the maneuver \
(the default is ``None``)
Notes
-----
This methods updates the value of :attr:`position`.
Any provided ``kwargs`` are forwarded to the :attr:`transition_model`.
If `timestamp`` is ``None``, the method has no effect, but will return successfully.
"""
if self.state.timestamp is None:
self.state.timestamp = timestamp
return
# Compute time_interval
try:
time_interval = timestamp - self.state.timestamp
except TypeError:
# TypeError: (timestamp or prior.timestamp) is None
return
if self.transition_model is None:
raise AttributeError('Platform without a transition model cannot be moved')
state_vector = self.transition_model.function(state=self.state,
noise=noise,
timestamp=timestamp,
time_interval=time_interval,
**kwargs)
new_state = State.from_state(self.state, state_vector=state_vector, timestamp=timestamp)
self.states.append(new_state)
[docs]
class MultiTransitionMovable(MovingMovable):
"""Moving platform with multiple transition models
A list of transition models are given with corresponding transition times, dictating the
movement behaviour of the platform for given durations.
"""
transition_models: Sequence[TransitionModel] = Property(doc="List of transition models")
transition_times: Sequence[datetime.timedelta] = Property(doc="Durations for each listed "
"transition model")
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
if len(self.transition_models) != len(self.transition_times):
raise AttributeError('transition_models and transition_times must be same length')
self.transition_index = 0
self.current_interval = self.transition_times[0]
@property
def transition_model(self):
return self.transition_models[self.transition_index]
[docs]
def move(self, timestamp=None, noise=True, **kwargs) -> None:
"""Propagate the platform position using the :attr:`transition_model`.
Parameters
----------
timestamp: :class:`datetime.datetime`, optional
A timestamp signifying the end of the maneuver (the default is ``None``)
Notes
-----
This methods updates the value of :attr:`position`.
Any provided ``kwargs`` are forwarded to the :attr:`transition_model`.
If :attr:`transition_model` or ``timestamp`` is ``None``, the method has
no effect, but will return successfully.
This method updates :attr:`transition_model`, :attr:`transition_index` and
:attr:`current_interval`:
If the timestamp provided gives a time delta greater than :attr:`current_interval` the
:attr:`transition_model` is called for the rest of its corresponding duration, and the move
method is called again on the next transition model (by incrementing
:attr:`transition_index`) in :attr:`transition_models` with the residue time delta.
If the time delta is less than :attr:`current_interval` the :attr:`transition_model` is
called for that duration and :attr:`current_interval` is reduced accordingly.
"""
if self.state.timestamp is None:
self.state.timestamp = timestamp
return
try:
time_interval = timestamp - self.state.timestamp
except TypeError:
# TypeError: (timestamp or prior.timestamp) is None
return
temp_state = self.state
while time_interval.total_seconds() != 0:
if time_interval >= self.current_interval:
temp_state_vector = self.transition_model.function(
state=temp_state,
noise=noise,
time_interval=self.current_interval,
**kwargs
)
temp_state = State.from_state(self.state,
state_vector=temp_state_vector,
timestamp=timestamp)
time_interval -= self.current_interval
self.transition_index = (self.transition_index + 1) % len(self.transition_models)
self.current_interval = self.transition_times[self.transition_index]
else:
temp_state_vector = self.transition_model.function(
state=temp_state,
noise=noise,
time_interval=time_interval,
**kwargs
)
temp_state = State.from_state(self.state,
state_vector=temp_state_vector,
timestamp=timestamp)
self.current_interval -= time_interval
break
self.states.append(temp_state)
def _get_rotation_matrix(vel: StateVector) -> np.ndarray:
""" Generates a rotation matrix which can be used to determine the
corrected sensor offsets.
In the 2d case this returns the following rotation matrix
[cos[theta] -sin[theta]]
[cos[theta] sin[theta]]
In the 3d case this will be a 3x3 matrix which rotates around the Z axis
followed by a rotation about the new Y axis.
Parameters
----------
vel : StateVector
Dx1 vector denoting platform velocity in D dimensions
Returns
-------
np.array
DxD rotation matrix
"""
if len(vel) == 3:
return _rot3d(vel)
elif len(vel) == 2:
theta = _get_angle(vel, np.array([[1, 0]]))
if vel[1] < 0:
theta *= -1
return np.array([[cos(theta), -sin(theta)],
[sin(theta), cos(theta)]])
else:
raise NotImplementedError
def _get_angle(vec: StateVector, axis: np.ndarray) -> float:
""" Returns the angle between a pair of vectors. Used to determine the
angle of rotation required between relative rectangular cartesian
coordinate frame of reference and platform inertial frame of reference.
Parameters
----------
vec : StateVector
1xD array denoting platform velocity
axis : np.ndarray
Dx1 array denoting sensor offset relative to platform
Returns
-------
Angle : float
Angle, in radians, between the two vectors
"""
vel_norm = vec / np.linalg.norm(vec)
axis_norm = axis / np.linalg.norm(axis)
return np.arccos(np.clip(np.dot(axis_norm, vel_norm), -1.0, 1.0))
def _rot3d(vec: np.ndarray) -> np.ndarray:
"""
This approach determines the platforms attitude based upon its velocity
component. It does not take into account potential platform roll, nor
are the components calculated to account for physical artifacts such as
platform trim (e.g. aircraft yaw whilst flying forwards).
The process determines the yaw (x-y) and pitch (z to x-y plane) angles.
The rotation matrix for a rotation by yaw around the Z-axis is then
calculated, the rotated Y axis is then determined and used to calculate the
rotation matrix which takes into account the platform pitch
Parameters
----------
vec: StateVector
platform velocity
Returns
-------
np.ndarray
3x3 rotation matrix
"""
return _rot3d_tuple(tuple(vec.flat))
@lru_cache(maxsize=128)
def _rot3d_tuple(vec: tuple) -> np.ndarray:
""" Private method. Should not be called directly, only from `_rot3d`
Params and returns as :func:`~_rot3d`
This wrapped method takes a tuple rather than a state vector. This allows caching, which
is important as the new sensor approach means `_rot3d` is called on each call to get_position,
and becomes a significant performance hit.
"""
# TODO handle platform roll
yaw = np.arctan2(vec[1], vec[0])
pitch = np.arctan2(vec[2],
np.sqrt(vec[0] ** 2 + vec[1] ** 2)) * -1
rot_z = rotz(yaw)
# Modify to correct for new y axis
y_axis = np.array([0, 1, 0])
rot_y = expm(np.cross(np.eye(3), np.dot(rot_z, y_axis) * pitch))
return np.dot(rot_y, rot_z)
```