This material was sent in by John Vickers; it is a model to correct
systematics in the PPMXL proper motion for objects with J magnitudes.

John's original submission should be in the directory as recenter_and_test.zip.

Markus Nullmeier then added code to do linear interpolation using
healpixes.  That interpolation is essentially sane, as shown in the
deviation*pdf files.

To update the vickers_pm* columns in the database, run

$ add_vickers_pms.sh

(this is a thin wrapper around a PSQL defining and calling the functions).
This assumes psql gavo will give you a superuser account in the right database.
Errors about not being able to create or drop the plpython extension are
harmless and can be ignored.

This needs pmr.csv, pmd.csv, and recenter.py on the DB server exactly where it
is on the DaCHS server in case they're different, which they are on GAVO's
DC.  There, you have to run

scp *.csv recenter.py rigel:/data/gavo/inputs/ppmxl/johnspms/

after changes.