Fitting a rotation curve

velfit is a task to fit a rotation curve to an isovelocity image of a rotating disk. This is classical ``moment analysis''.

VELFIT
in=inten,veloc
centre=0,-60	Rotation centre is 60 arcsec south of map centre.
pa=40	Position angle of major axis.
incline=65	The believed inclination of the disk.
vsys=440	Systemic velocity of the galaxy.
log=rot.log	File to hold results - defaults to terminal.

inten is the (x,y) intensity distribution of data.cube integrated over the z (velocity) axis. It is obtained using moment as follows:

MOMENT
in=data.cube
out=iten
mon=-1	Get average intensity.
axis=3	Squash along the third axis
clip=-2.0,0.0	Or whatever.

veloc is an (x,y) model for the velocity values, a mean velocity image. It would be obtained as follows:

MOMENT
in=data.cube	Input dataset.
out=veloc	The output dataset.
mon=1	First order moment.
axis=3	Squash along the third axis
clip=-2.0,0.0	Or whatever.