Spilhaus, as it flows downstream from PROJ: R

The same document rendered on three Ubuntu runners that differ only in where GDAL and PROJ come from. Each page's first table says what that runner had.

• stock Ubuntu 24.04 (apt) - GDAL 3.8.4 / PROJ 9.4.0 at the time of writing; no Spilhaus expected
• ubuntugis-unstable PPA - newer GDAL, but PROJ is whatever the PPA carries
• conda-forge - one libproj shared by every package, all prebuilt

Companions: index, the Python notebook, the browser version, and the source spilhaus.qmd.