Hello all,

If you use Find_Orb with astrometry from AstDyS/NEODyS in the .rwo
format, _or_ if you use Monte Carlo variant orbits from Find_Orb, you
should read the following (and get the current version of the program).
If you don't do either of those things, you can stop reading, relax,
and delete this e-mail.

If you _have_ been doing those things, you definitely should get
the current software. The bugs are serious enough that I'm cross-posting
from the Find_Orb list to the MPML one, not something I'd normally do,
in hopes of getting this out to anyone affected by these bugs.

First, the problem with .rwo files :

https://projectpluto.com/findhist.htm#rwo_bug

I was treating the 'RMS' fields in .rwo files as if they were an
estimate of astrometric uncertainty. Unfortunately, they are multiplied
by the square root of the number of observations made on that night from
that observatory... not something I ever would have expected.

This has some really unpleasant consequences (described at the above
link). Fortunately, I was able to _divide_ the sigmas by that same
quantity, restoring the sigmas to what you'd normally expect. So you
can now use .rwo data without trouble. But if you've generated orbits
with Find_Orb and .rwo data in the last couple of years, the weighting
of observations has been wrong.

Second, the problem with Monte Carlo variant orbits :

https://projectpluto.com/findhist.htm#sat_offsets_bug

This problem occurs if there are observations from satellites (WISE,
SOHO, STEREO, Hubble, etc.) You're fine until you generate MC
variant orbits. The moment you do that, Find_Orb zeroes the offset
between the satellite observer and the geocenter. So it's as if those
observations were made from the geocenter. Which, of course, they were
not.

WISE has been particularly active, so this has affected a _lot_ of
MC results from Find_Orb.

I've posted fixed versions of the Windows software (32-bit and 64-bit).
The source code on GitHub is fixed; get that if you're on Linux or OS/X.
The on-line version of Find_Orb ( https://www.projectpluto.com/fo.htm )
is also fixed.

My thanks to Daniel Bamberger and Marco Micheli for pointing out these
bugs and helping me to figure out what was going wrong here. Please let
me know if you've questions about any of this.

-- Bill