Create robots.py

2014-09-07 21:11:18 -04:00
parent c9c5f5d34c
commit 13bcb65c64
1 changed files with 113 additions and 0 deletions
--- a/python/breezyslam/robots.py
+++ b/python/breezyslam/robots.py
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+'''
+BreezySLAM: Simple, efficient SLAM in Python
+
+robots.py: odometry models for different kinds of robots
+
+Copyright (C) 2014 Suraj Bajracharya and Simon D. Levy
+
+This code is free software: you can redistribute it and/or modify
+it under the terms of the GNU Lesser General Public License as 
+published by the Free Software Foundation, either version 3 of the 
+License, or (at your option) any later version.
+
+This code is distributed in the hope that it will be useful,     
+but WITHOUT ANY WARRANTY without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU Lesser General Public License 
+along with this code.  If not, see <http:#www.gnu.org/licenses/>.
+You should also have received a copy of the Parrot Parrot AR.Drone 
+Development License and Parrot AR.Drone copyright notice and disclaimer 
+and If not, see 
+<https:#projects.ardrone.org/attafchments/277/ParrotLicense.txt> 
+and
+<https:#projects.ardrone.org/attachments/278/ParrotCopyrightAndDisclaimer.txt>.
+'''
+
+'''
+Change Log:
+
+01-MAR-2014: Simon D. Levy - Initial release
+19-MAR-2014: SDL           - Added Laser class
+31-MAR-2014: SDL           - Robot.computeVelocities returns dtheta in degrees
+01-MAY-2014: SDL           - Migrated Laser class to C extension
+04-MAY-2014: SDL           - Changed from meters to millimeters
+'''
+
+import math
+
+class WheeledRobot(object):
+    '''
+    An abstract class supporting ododmetry for wheeled robots.  Your implementing
+    class should provide the method:
+    
+      extractOdometry(self, timestamp, leftWheel, rightWheel) --> 
+        (timestampSeconds, leftWheelDegrees, rightWheelDegrees)      
+    '''
+    
+    def __init__(self, wheelRadiusMillimeters, halfAxleLengthMillimeters):
+        '''
+        wheelRadiusMillimeters    radius of each odometry wheel   
+        halfAxleLengthMillimeters half the length of the axle between the odometry wheels  
+        '''
+        self.wheelRadiusMillimeters = wheelRadiusMillimeters  
+        self.halfAxleLengthMillimeters = halfAxleLengthMillimeters
+        
+        self.timestampSecondsPrev = None        
+        self.leftWheelDegreesPrev = None
+        self.rightWheelDegreesPrev = None
+                
+    def __str__(self):
+        
+        return '<Wheel radius=%f mm Half axle Length=%f mm>' % \
+        (self.wheelRadiusMillimeters, self.halfAxleLengthMillimeters)
+        
+    def __repr__(self):
+        
+        return self.__str__()
+        
+    def computeVelocities(self, timestamp, leftWheelOdometry, rightWheelOdometry):
+        '''
+        Computes forward and angular velocities based on odometry.
+        
+        Parameters:
+        
+          timestamp          time stamp, in whatever units your robot uses       
+          leftWheelOdometry  odometry for left wheel, in whatever form your robot uses       
+          rightWheelOdometry odometry for right wheel, in whatever form your robot uses
+        
+        Returns a tuple (dxyMillimeters, dthetaDegrees, dtSeconds)
+        
+          dxyMillimeters     forward distance traveled, in millimeters
+          dthetaDegrees change in angular position, in degrees
+          dtSeconds     elapsed time since previous odometry, in seconds
+        '''                      
+        dxyMillimeters = 0
+        dthetaDegrees = 0
+        dtSeconds = 0
+                       
+        timestampSecondsCurr, leftWheelDegreesCurr, rightWheelDegreesCurr = \
+            self.extractOdometry(timestamp, leftWheelOdometry, rightWheelOdometry)
+            
+        if self.timestampSecondsPrev != None:  
+            
+            leftDiffDegrees = leftWheelDegreesCurr - self.leftWheelDegreesPrev
+            rightDiffDegrees = rightWheelDegreesCurr - self.rightWheelDegreesPrev
+            
+            dxyMillimeters =  self.wheelRadiusMillimeters * \
+                    (math.radians(leftDiffDegrees) + math.radians(rightDiffDegrees))
+               
+            dthetaDegrees =  (float(self.wheelRadiusMillimeters) / self.halfAxleLengthMillimeters) * \
+                    (rightDiffDegrees - leftDiffDegrees)
+                
+            dtSeconds = timestampSecondsCurr - self.timestampSecondsPrev
+                
+        # Store current odometry for next time
+        self.timestampSecondsPrev = timestampSecondsCurr        
+        self.leftWheelDegreesPrev = leftWheelDegreesCurr
+        self.rightWheelDegreesPrev = rightWheelDegreesCurr
+
+        # Return linear velocity, angular velocity, time difference
+        return dxyMillimeters, dthetaDegrees, dtSeconds 
+