Bug summary

With Matplotlib 3.8+ I'm seeing spurious lines that get added with manually labeled contours via clabel.

It seems to only happen in locations where the contours are more complex or near those areas, but I haven't been able to track down why this happens.

Code for reproduction

Example code (here working with Matplotlib <3.8): https://geocat-examples.readthedocs.io/en/latest/gallery/Contours/NCL_coneff_8.html

I'll work on stripping down this example though.

Actual outcome

when run in a script that provided a manual list of contour label locations:

when locations were manually clicked:

Expected outcome

similar, but without the spurious straight lines.

Additional information

What are the conditions under which this bug happens?

• happens with both "clicked" and specified manual contour labels in certain locations
• seems to happen only near areas with more complex contours
• interestingly, this also happens when you specify contour label locations this way on a cartopy map and the specified points are not on the projected map. however, this is not the case here.
  Has this worked in earlier versions?
• worked prior to 3.8
  Do you know why this bug is happening?
• unfortunately, no. will look into it a bit more though.

Operating system

OS/X

Matplotlib Version

3.8.1

Matplotlib Backend

MacOSX

Python version

Python 3.11.6

Jupyter version

4.0.8

Installation

conda