Fix RuntimeError in RandomPath._new_goal(): x must be a sequence

[atditto]

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Common issues

Describe the bug
When using the RandomPath driver and running a robot simulation, a RuntimeError is raised when attempting to update the goal marker position: RuntimeError: x must be a sequence

Version information

Did you install from PyPI or GitHub?

• Installed from: PyPI(pip install rvc3python)
• Robotics Toolbox version: 1.1.1
• Swift: 1.1.0
• SpatialMath toolbox: version 1.1.14

Robotics Toolbox depends heavily on two other packages: Swift (3D graphics) and SpatialMath toolbox (underpinning maths utilities). If you think your issue is related to these, then please answer the questions above for them.

To Reproduce
Example code:

import numpy as np
from spatialmath import *
from spatialmath.base import *
from roboticstoolbox import *

V = np.diag([0.02, np.deg2rad(0.5)]) ** 2
robot = Bicycle(covar=V, animation="car")
robot.control = RandomPath(workspace=10)
robot.run(T=10);

Output:

(rvc-sim) PS D:\repos\rvc-sim> & d:/repos/rvc-sim/.venv/Scripts/python.exe d:/repos/rvc-sim/temp.py
Traceback (most recent call last):
  File "d:\repos\rvc-sim\temp.py", line 9, in <module>
    robot.run(T=10);
  File "D:\repos\rvc-sim\.venv\lib\site-packages\roboticstoolbox\mobile\Vehicle.py", line 460, in run
    self.step(animate=animate)
  File "D:\repos\rvc-sim\.venv\lib\site-packages\roboticstoolbox\mobile\Vehicle.py", line 672, in step
    u = self.eval_control(self._control, self._x)
  File "D:\repos\rvc-sim\.venv\lib\site-packages\roboticstoolbox\mobile\Vehicle.py", line 330, in eval_control
    u = control.demand()
  File "D:\repos\rvc-sim\.venv\lib\site-packages\roboticstoolbox\mobile\drivers.py", line 233, in demand
    self._new_goal()
  File "D:\repos\rvc-sim\.venv\lib\site-packages\roboticstoolbox\mobile\drivers.py", line 275, in _new_goal
    self._goal_marker.set_xdata(self._goal[0])
  File "D:\repos\rvc-sim\.venv\lib\site-packages\matplotlib\lines.py", line 1304, in set_xdata
    raise RuntimeError('x must be a sequence')
RuntimeError: x must be a sequence

Expected behavior
The simulation should be started correctly.

Screenshots
If applicable, add screenshots to help explain your problem.

Environment (please complete the following information):

• Windows
• Python 3.10.11

Additional context
The error occurs because matplotlib.lines.Line2D.set_xdata() expects an iterable input (like a list or array), but a scalar value was passed instead.

Temporary fix:
In drivers.py, locate the RandomPath._new_goal() method and change:

self._goal_marker.set_xdata(self._goal[0])
self._goal_marker.set_ydata(self._goal[1])

to:

self._goal_marker.set_xdata([self._goal[0]])
self._goal_marker.set_ydata([self._goal[1]])

This ensures compatibility with Matplotlib's plotting interface and avoids the runtime error.