Simple Continuous Curvature Path Library in Python

This library implements the calculation of simple continuous curvature paths as described by the paper of Scheuer and Fraichard in python:

@inproceedings{scheuer1997continuous,
  title={Continuous-curvature path planning for car-like vehicles},
  author={Scheuer, Alexis and Fraichard, Thierry},
  booktitle={Intelligent Robots and Systems, 1997. IROS'97., Proceedings of the 1997 IEEE/RSJ International Conference on},
  volume={2},
  pages={997--1003},
  year={1997},
  organization={IEEE}
}

License

GPLv3 - please contact me if you need the software under a different license.

Example use - single Turn

input

kappa_max = Max curvature == 1/r of the inner curve radius r

sigma_max = The steering rate, i.e., the sharpness of the turn

output

Static Turn info:

Turn.len = Length of the complete turn
Turn.len_of_circular_part
Turn.state_qg = Endpoint of the turn

State: (sequence of trajectory points)

x, y = positions
theta = angle
kappa = curvature == 1/r of the curve radius

use

import numpy as np
from scc.turn import Turn
from scc.turnparams import TurnParams

# set parameters:
tparam = TurnParams(_kappa_max=1.8,
                    _sigma_max=1.0)

# setup a single turn:
turn = Turn(_params=tparam, _delta=math.pi*0.76)

# calculate a set of trajectory points:
XT = np.linspace(0, turn.len, 128, endpoint=True)
tra = turn.state(XT)
print (tra.x)
print (tra.y)

Or more complete: plot_curve.py

Example use - Scc Path

import numpy as np
from scc.turn import Turn
from scc.turnparams import TurnParams

# set parameters:
pos1 = State(_x=-3.0, _y=6.4, _theta=math.pi*0.7, _kappa=0)
pos1 = State(_x=10.0, _y=8.2, _theta=math.pi*0.55, _kappa=0)
tparam = TurnParams(_kappa_max=1.8,
                    _sigma_max=1.0)

PATHOPTIONS = [PathType.lsl, PathType.rsr, PathType.rsl, PathType.lsr]
paths = [SccPathVariant(tparam, pos1, pos2, variant) for variant in
         PATHOPTIONS]
shortest_path = min(paths, key=lambda path: path.len)

# calculate positions:
X = np.linspace(0, shortest_path.len, 128, endpoint=True)
tra = shortest_path.state(X)
print (tra.x)
print (tra.y)

Or more complete: plot_path.py

TODOs

• improve documentation
• Add support for the case of: om12_dist <= 2 * self.params.outer_rad. I.e., when the centers of the two circles are very close together! (PathType.lrl, PathType.rlr)
• Add unit tests
• add setup.py to install via pip