Scans for plates taken to search for Trojans by the Palomar and Leiden
observatories.

docs/plate-combined.txt is generated by invoking bin/concat_meta.py

docs/plate-emulsion.txt contains all emulsions for the 1960 survey (2017-01-19)

There are defaults for emulsion and filter in calibrate.py, but they may be not
sensible enough.

List of papers / surveys:

A + A Suppl 1970   2.339   The Palomar-Leiden survey of faint Minor Planets

A J         1970  75.659   Minor Planets and Related Objects:
				The density of Trojans near the Preceding Lagrangian Point

Icarus      1984  59.1     The Palomar-Leiden survey of faint minor
						planets - Conclusion

A + A       1989 224.299   The 1977 Palomar-Leiden Trojan survey

Icarus      1991  91.326   The second Palomar-Leiden Trojan survey

There are some extra plates (unused by van Houtens because there are various
issues with them) in:

* 1972Mar_Tx (this is, different from the rest of them, on plates
  25.4x25.4 cm -- ok, 10in x 10in)
* 1971Mar_Apollo

For most of these we've been able to reconstruct metadata (if with
somewhat lesser confidence), mostly based on a box with index cards in
Gernot Burkart's office.  Unclear and unused at this point are:
06679_1.fits, 06679_2.fits, nolab_1.fits, nolab_2.fits (where "nolab" is
pretty certainly is "no label", and hence it's simply not clear what
these plates are.


Milcho Tsvetkov kindly scanned the index cards.  The comparison to the plate
list showed the following:

* We don't have index cards for the plates in boxes 6, 7, 11, 12, 13, and
	most of 14, i.e., the surveys 1971Mar_T1S, 1977Oct_T3S, 1971Mar_Apollo.
* We have index cards but no plates for plates 6673, 6680, and 6681.