The GPOINT syntax is similar to the POINTING command. The full syntax of the GPOINT command is
GPOINT /LENGTH\_GPT <arcsec>
/TIME\_GPT <time(s)> /NUMBER <pts>
/SUB\_PT <nsub(total)> [BY\_2]
/ORIENTATION <direction(L,B,A,E)> [ONLY]
Where <arcsec> is the length of each arm of the cross in arcsec, <time(s)> is the length of time in seconds spent averaging the signal at each point on the cross, <pts> is the number of points on each arm of the cross, <nsub(total)> is the sum of the number times <pts> observations are made on both arms of the cross (should be an even number), BY_2 if present means that measurements along the arms of the cross should be done alternately, two at a time (forward and reverse; and <nsub> ought to be a multiple of 4), otherwise <nsub>/2 scans are done on one arm (alternating forward and reverse) followed by the remainder on the other arm, <direction(L,B,A,E)> is the direction of the first arm of the cross: L=LONGITUDE/R.A., B=LATITUDE/DEC., A=AZIMUTH, E=ELEVATION, and ONLY if present means do NOT do the perpendicular arm of the cross.
The GPOINT command is too new to have ``usual'' values. We expect that <arcsec> ought to be 32 arcsec at 1.3 mm wavelength, 22 arcsec at 0.9 mm if <pts> is 3. Alternatively, if better results are obtained with <pts> = 5, <arcsec> ought to be increased by about 30%: 42 and 29, respectively. /TIM should be 20-30, and /SUB between 4-10 depending on the strength of the source and the repeatability. BY_2 should only be specified if /SUB is 8. GPOINT should not be used on planets or strong radio sources, as the dead time between subscans will make POINTING more efficient.
There are several options for the fit Chef performs on the GPOINT data. The fitted curve can be a Gaussian or a Parabola. The default is parabola.
OBST> MBC SUPPLY GRIDPOINT GAUSSIAN
or
OBST> MBC SUPPLY GRIDPOINT PARABOLA
changes Chef's action. The parabolic fit takes much less time and is the
better choice if <pts> is only 3. The center points of one arm may be used in
the fit of the opposite arm (the default). This may not be a good idea if the
atmospheric emission is changing significantly with time. To prevent this, and
accept only center points bracketted in time by the two end points, type
OBST> MBC SUPPLY GRIDPOINT BRACKET
or
OBST> MBC SUPPLY GRIDPOINT NOBRACKET
to restore the default.