"fig.region" is not updated to the "region" of the current plot | Wrong lines via hlines and vlines

[yvonnefroehlich]

Description of the problem

To get the region of the a PyGMT Figure, fig.region can be used. In case a figure contains different plots with different regions, fig.region always provides the region related to the first plot. This affects the hlines and vlines methods. By default, a line is plotted extending over the complete plotting region. This leads to unexpected / wrong lines for the second and following plots, as the region values related to the first plot are used. A workaround is to explicitly specify the limits.

Minimal Complete Verifiable Example

import pygmt

fig = pygmt.Figure()

fig.basemap(region=[-1, 1, -1, 1], projection="X4c", frame=1)
print(fig.region)  # [-1.  1. -1.  1.]
fig.hlines(y=0)
fig.vlines(x=0)

fig.shift_origin(xshift="w+1c")

fig.basemap(region=[-2, 2, -2, 2], projection="X4c", frame=1)
print(fig.region)  # still [-1.  1. -1.  1.]
fig.hlines(y=0)
fig.vlines(x=0)

fig.show()

Full error message

NaN.

System information

PyGMT information:
  version: v0.14.1.dev10
System information:
  python: 3.12.3 | packaged by conda-forge | (main, Apr 15 2024, 18:20:11) [MSC v.1938 64 bit (AMD64)]
  executable: C:\ProgramData\Anaconda3\envs\pygmt_env_dev_650\python.exe
  machine: Windows-10-10.0.19045-SP0
Dependency information:
  numpy: 1.26.4
  pandas: 2.2.0rc0
  xarray: 2024.3.0
  netCDF4: 1.6.5
  packaging: 24.0
  contextily: 1.6.0
  geopandas: 0.14.3
  IPython: 8.22.2
  pyarrow: None
  rioxarray: 0.15.4
  gdal: 3.8.2
  ghostscript: 10.03.0
GMT library information:
  version: 6.5.0
  padding: 2
  share dir: C:/Program Files (x86)/gmt6/share
  plugin dir: C:/ProgramData/Anaconda3/envs/pygmt_env_dev_650/Library/bin/gmt_plugins
  library path: C:/ProgramData/Anaconda3/envs/pygmt_env_dev_650/Library/bin/gmt.dll
  cores: 4
  grid layout: rows
  image layout: 
  binary version: 6.5.0

[seisman]

I can confirm the bug. Figure.region calls the Session.extract_region method, which wraps the GMT_Extract_Region API function.

The GMT_Extract_Region API function opens the "hidden" PS file and reads the information from lines with the PROJ tag, so it can only find the first "region".