JAC Style guide: template
 v2y-x2y Angle Problem
In January Fred Baas uncovered an obscure bug in the real-time telescope software which has caused GSD
data file headers to be incorrect under certain (rare) conditions when V2Y was not equal to 0.0. The cause
has now been found and fixed by Firmin Oliveira. The data itself are fortunately correct. From the JCMT
database it appears only 4 projects have been affected since 1989 and the affected observer has been
notified. If in doubt please check the list of projects NOTaffected but which had V2Y's not equal
to 0.0. You can find this list on the World-Wide Web at URL:
/~rpt/v2y_not.html.
Although we believe we identified all scans affected, we think a general warning is appropriate. However,
given the rare occurance of the situation, I will omit a detailed explanation and just present the conditions
under which the error would have happened:
If during your observations you had:
l defined a PA angle for the Y-axis of the CELL (V2Y) of
90 < V2Y < 180 for a RA-Dec cell or
180 < V2Y < 270 for an AZ-EL cell
...and...
l done a fivepoint AFTER defining V2Y
...and...
l observed at offsets positions -not (0,0)- after the fivepoint
then SPECX will map/locate the part of the observations following the fivepoint at a X grid-point with the
opposite sign of what it should be.
The most obvious projects which might be affected are ones which align the Y-axis of the cell with the
major axis of a galaxy, strictly following the astronomical conventions by using V2Y of e.g. 120
degrees
instead of -60 or 300 degrees.
Remo Tilanus, JAC
Last Modification Date 1996/04/08 - Last Modification Author: Graeme Watt (gdw)
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