Directions for Making & Displaying a Focus Drift Scan Observation
	Bill Peters						20 Apr 00


    Focus drift scans are only available through a crude OBST macro, and the
results can only be viewed via some other macros and the GRAPHIC program: 

    For a focus drift in Z, in the OBST window type

	@TEL$OBS:FOCUS_DRIFT <length> <time> <repeats>

where <length> is the length in mm, <time> is the length of time per drift
(minutes), and <repeats> is the number of times to repeat the drift.  (For
Uranus at 272 GHz, I used 6 mm (about 5 times the wavelength), 3 minutes, and 
repeated 6 times.)  If you omit the parameters, you will be prompted for
them.  This will start an observation (so long as none is already in progress)
of <repeats> subscans.  The FCZ in a large font on the SDH display shows the
current Z focus position during the subscan, relative to the center position
specified by the CORRECTIONS command.

    (A focus drift in X can be done the same way, but type XFOCUS_DRIFT instead 
of FOCUS_DRIFT.  The <length> in X should be 2 times that in Z.)

    OBST and TOOLBOX will produce no sensible display after the scan is
over.  To extract the data and view it, do the following in an SMTSYS window:

	SD KDATA:[SMT]
	@GET_DRIFT <scan number>

This script converts the Raw Data to ASCII, extracts the intensity and focus
positions from it, and writes it in a file named JUNK.<scan number>.  To
view the data, next do

	GRAPHIC
	DEVICE XLAND BLACK
	@TEL$POINTING:I_VS_FOCUS JUNK.<scan number>

(or     @TEL$POINTING:I_VS_FOCUSX JUNK.<scan number>
if it was an X focus drift.)

This will produce a plot with points each representing a single DRUMBEAT 
integration.  (The integration time is determined by WFRQ of the WOBBLE and 
PREINT of the DRUMBEAT commands in OBST.)  The X axis will be the focus Z
position in microns.  Unfortunately, these are absolute positions after the
homology focus model is added to the CORRECTIONS FCZ parameter.  That is,
it is the same Z as displayed in a small font in the SDH window and NOT the
FCZ position displayed by SDH in a large font during the subscan.  The 
data in the plots are stored in GRAPHIC arrays FCZ[NFCZ] and INT[NFCZ] (in
chronological order).  NFCZ is set to the number of data points found in
JUNK.<scan number>. 

    If you want to plot a smoothed version of the individual points on the
GRAPHIC plot:

	@TEL$POINTING:FOCUS_BIN FCZ INT NFCZ BFCZ BINT 200

Here BFCZ and BINT are new GRAPHIC arrays where the macro will store in array 
BINT, binned averages of the INT array data.   BFCZ is the Z corresponding to
the center of the bin.  The last parameter (200 above) is the number of
bins to define.  You can increase or decrease this value as you wish.  (The
names, BFCZ and BINT, can also be changed at will.)

    For X drifts, substitute X's for the Z's in the above.