fin_model.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 as np
from tf_quaternion.transformations import quaternion_matrix
from uuv_gazebo_ros_plugins_msgs.msg import FloatStamped


class FinModel(object):
    def __init__(self, index, pos, quat, topic):
        self.id = index
        self.pos = pos
        self.quat = quat
        self.topic = topic
        self.rot = quaternion_matrix(quat)[0:3, 0:3]

        unit_z = self.rot[:, 2]
        # Surge velocity wrt vehicle's body frame
        surge_vel = np.array([1, 0, 0])
        fin_surge_vel = surge_vel - np.dot(surge_vel, unit_z) / np.linalg.norm(unit_z)**2 * unit_z        
        # Compute the lift and drag vectors
        self.lift_vector = -1 * np.cross(unit_z, fin_surge_vel) / np.linalg.norm(np.cross(unit_z, fin_surge_vel))
        self.drag_vector = -1 * surge_vel / np.linalg.norm(surge_vel)       

        self.pub = rospy.Publisher(self.topic, FloatStamped, queue_size=3)
    
    def publish_command(self, delta):
        msg = FloatStamped()
        msg.header.stamp = rospy.Time.now()
        msg.data = delta
        self.pub.publish(msg)