LinAlgError: Matrix is not positive defined

[rodja]

In simulation, I just got a weird error:

2025-06-23 05:18:33.191 [ERROR] rosys/event.py:85: could not emit listener=EventListener(callback=<bound method RobotLocator._handle_gnss_measurement of <field_friend.robot_locator.RobotLocator object at 0x14d635f50>>, filepath='/Users/rodja/Projects/field_friend/field_friend/robot_locator.py', line=48)
Traceback (most recent call last):
  File "/Users/rodja/Projects/field_friend/field_friend/robot_locator.py", line 173, in _update
    L = np.linalg.cholesky(S)
        ^^^^^^^^^^^^^^^^^^^^^
  File "/Users/rodja/Projects/field_friend/.venv/lib/python3.11/site-packages/numpy/linalg/linalg.py", line 779, in cholesky
    r = gufunc(a, signature=signature, extobj=extobj)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/rodja/Projects/field_friend/.venv/lib/python3.11/site-packages/numpy/linalg/linalg.py", line 115, in _raise_linalgerror_nonposdef
    raise LinAlgError("Matrix is not positive definite")
numpy.linalg.LinAlgError: Matrix is not positive definite

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/rodja/Projects/field_friend/.venv/lib/python3.11/site-packages/rosys/event.py", line 77, in emit
    result = listener.callback(*args, **kwargs)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/rodja/Projects/field_friend/field_friend/robot_locator.py", line 160, in _handle_gnss_measurement
    self._update(z=np.array(z), h=np.array(h), H=H, Q=Q)
  File "/Users/rodja/Projects/field_friend/field_friend/robot_locator.py", line 177, in _update
    L = np.linalg.cholesky(S)
        ^^^^^^^^^^^^^^^^^^^^^
  File "/Users/rodja/Projects/field_friend/.venv/lib/python3.11/site-packages/numpy/linalg/linalg.py", line 779, in cholesky
    r = gufunc(a, signature=signature, extobj=extobj)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/rodja/Projects/field_friend/.venv/lib/python3.11/site-packages/numpy/linalg/linalg.py", line 115, in _raise_linalgerror_nonposdef
    raise LinAlgError("Matrix is not positive definite")
numpy.linalg.LinAlgError: Matrix is not positive definite

The error does not only appear once but in super high frequency. After a restart the error is gone.

[pascalzauberzeug]

Seems like this is caused by too small uncertainty values while calculating the Kalman Gain.
Increasing the GNSS standard deviation helps in simulation, but will lead to failing tests because of the bigger positional error.