Subject: GRIM orientation

From: Russet McMillan

Submitted: Mon, 27 Aug 2001 21:01:59 -0600 (MDT)

Message number: 518 (previous: 517, next: 519 up: Index)

This is an important note for GRIM observers; the orientation of the
instrument has been changed!  A mistake made many years ago and
honored in the intervening years has been corrected, and the
instrument will be 180 degrees from its previous orientation.  The
correction grants some benefits to the observing specialists, but
unfortunately for observers the change will mostly be a nuisance.

The information on the Orientation and Offset Direction web page at
http://www.apo.nmsu.edu/Instruments/offsets.html is now correct for
GRIM (information for other instruments may be out of date and will be
checked soon).  In f/5 configuration, North is now up on the chip, and
East is to the left.  If observers prefer the old North down/East
right configuration, they can slew with a rotation of 180 degrees in
Remark.  However, the directions of instrument offsets will still be
as shown on the page: a +X offset from Remark or the MC moves the star
to the right regardless of rotation, and a +Y offset moves the star
down on the chip.

This may affect the behavior of some dither scripts. If it is
important to you to make sure that targets end up on a certain
quadrant of the chip, or that dither offsets are made in a particular
order, check the webpage and consult with the observing specialists to
see if you need to make any changes to your script.

				    Russet McMillan.


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