[guide-user] Flat-fielding/etc.

Bill J. Gray Mar 3, 2000

Hi folks,

DARKS/FLATS:

My inquiries about dark subtraction and flat-fielding drew some mixed
replies, mostly by private e-mail. About half the replies said that "of
course, any decent imaging software already has these functions built into
it... why duplicate them?" The other half said that "my software doesn't
have these functions... please add them to Charon."

I agree that in theory, the imaging software _ought_ to handle this
for you. But I'd seen enough noisy images to persuade me that, in the
real world, this is not the actual case.

I have zero desire to write a "real" image processing program. But
dark and flat subtraction is a minor enough project (and, from the images
I've seen, _needed_ enough) to persuade me to do it. In fact, it's done
now, aside from some testing.

MPCORB PROBLEMS:

I have zero idea why this is happening.

I briefly thought it possible that MPC had extended/modified the format,
resulting in this feature being 'broken'. But I've downloaded a current
MPCORB, and it looks fine and works correctly in Guide.

To those running into trouble with this, though: getting rid of MPCORB
alone is not enough to return to normal operation. The problem is that
Guide processes MPCORB and creates two files, ASTNAMES.DAT and a .AST
file, usually named something like 2451600.AST. (The number is a Julian
Day, and will vary depending on when you downloaded MPCORB or MPCORBCR.)
There are several reasons for this, including speed and attempting to
make the code for MPCORB resemble the "usual" asteroid drawing code as
closely as possible.

Anyway, delete ASTNAMES.DAT and 2451600.AST (or a similar .AST file),
and you should be in business. You can then try MPCORB again and see if
Guide handles it properly. Or, you can shut off MPCORB use by editing
STARTUP.MAR and looking for this line:

41 ast a li 0 2147483647 2451600

Change the '2451600' to '0', and Guide will return to drawing asteroids
from built-in data. This is a barbaric expedient, but I'm assuming Guide
is sufficiently "confused" that you can't just go into Extras and shut off
MPCORB use.

-- Bill