thruster_custom.py

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# Copyright (c) 2016 The UUV Simulator Authors.
# All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

import rospy
import numpy
from thruster import Thruster


class ThrusterCustom(Thruster):
    """Class describing a custom conversion curve between the command input,
    usually the angular velocity, and the correspondent output thrust force.
    Here the inverse of the conversion function can be computed so that the
    command for the desired thrust force is retrieved.
    The input vector corresponds to sampled values for the command input, and
    the output vector corresponds to the sampled values for the correspondent
    thrust forces.
    This information is usually available in the datasheet of the thruster's
    manufacturer.
    """
    LABEL = 'custom'

    def __init__(self, *args, **kwargs):
        """Class constructor."""
        super(ThrusterCustom, self).__init__(*args)

        if 'input' not in kwargs or 'output' not in kwargs:
            rospy.ROSException('Thruster input/output sample points not given')
        # Vector of sample values for each angular velocity
        self._input = kwargs['input']
        # Vector of sample values for each thrust force relative to the input
        self._output = kwargs['output']

    def get_command_value(self, thrust):
        # Compute the angular velocity necessary for the desired thrust force
        return numpy.interp(thrust, self._output, self._input)

    def get_thrust_value(self, command):
        """Computes the thrust force for the given command."""
        return numpy.interp(command, self._input, self._output)