Two Comments on Michaels's Pipeline

[Tom Droege <tdroege@veriomail.com>]

Comment 2.

Michael has named his combined (about page 16) image:  Mhra...

Seems to me, this is no longer a raw image.  Per tech note 30 I would have 
named this hmga... ??

This replaces the v or i with the m to show it is a combined V and I 
list.  The G is says it is an extracted star list a la Richmond.  Note we 
should allow for various combinations of bvri in the future.

Note that if we do this, then TN 30 needs an update to show the replacement 
of V,I with M.  Perhaps we can agree on some more letters.  Note now may be 
the time to agree on the use of the reserved letter a.

OK, it is a pain for Michael to worry about such things now, but it will 
get harder and harder to do it later.

Comment 1.

About page 8.

Michael is rounding off the exposures.  Not a bad idea but possibly the 
unrounded number is more correct.

Here is what I do:

I start a process that interrupts once a second.  I believe that this is 
not done very accurately.  OK, I just wrote a simple program to test 
this.  It looks like it is always a little short.  The spacing between two 
successive interrupts is .992 seconds.  But it wanders around. On interrupt 
it reads the computer clock.  This is in seconds since midnight with a 
resolution of (I think) 1/60 th second.

It then checks if the shutters are supposed to be opened.  If so it opens them.

It then checks to see if the shutters are open.  If they are, it takes the 
difference between the time the shutter was opened and the current 
time.  It compares this to the time the shutters were supposed to be kept 
open.  If this agrees to within 1/2 second, or if it is greater than the 
scheduled open time, the shutters are closed.  The time difference is 
recorded as the shutter open time.

The data collection loop is now started.

When the program is run, it comes to the place where the shutters are to 
open.  The program sets a flag to cause the shutters to open.  Then the 
program goes off to read out the last event.  Within a second the shutters 
will be opened by the interrupt.  When the read out is complete, it waits 
until the shutters are closed.  It then scans out the CCD to the memory 
card and goes back to the top of this paragraph to open the shutters for 
the next exposure.

OK, what I think this does is to record the exact time that the shutters 
were open to the resolution of the computer internal clock.  I remember 
1/60 th second.  It does this imperfectly because of the resolution of the 
QB interrupt process.  So the time as recorded is correct, this process 
just does not allow requesting a time more accurate than +/- 1/2 second.

Some of you will think this is an awful kludge.  But it is a lot better 
than the last scheme which seemed to have an occasional 10 second error.

Hope this helps describe the process.

Tom Droege