Documentation on velmodel

Task: velmodel
Purpose: Make a model image for a theoretical velocity pattern.
Categories: image analysis

        VELMODEL generates a MIRIAD image for a theoretical velocity
        pattern specified by model input paramaters. The default option
        is to make an image of the line-of-sight velocity corresponding
        to a rotating disk model:
          velocity = vsys +
        	(vrot*cos(theta-pa)+vrad*sin(theta-pa))*sin(incline)
        The output image can be combined with an intensity
        image to make a 3D model using the task VELIMAGE.

Key: in
        Input image name used as template for the output image.

Key: region
        Region of image to be used. The default region is the entire image.
        See documentation of region for details. All pixels within the
        bounding box are used; pixel masking is ignored.

Key: center
        The rotation center in arcsec from the center pixel, measured
        in the directions of RA and DEC. Default=0,0.

Key: pa
        Position angle of the major axis in degrees. Default is 0. (north).

Key: incline
        Inclination angle of the disk in degrees. Default is 0. (face on).

Key: radius
        Sample points along major axis in arcsecs. Need not be evenly spaced.
        At least one point must be given. 

Key: vrot
        Rotation curve in the plane of the disk specified by a power law:
        	rotation velocity = vrot(1)*(r/radius(1))**vrot(2)
        At least one point must be given. For options=sample, vrot gives the
        rotation velocity sampled at the radius points above, and is
        interpolated between the sample points, with zero velocity at zero
        radius, and not extrapolated beyond the last point. Units are km/s.

Key: vrad
        Radial velocity in plane of disk specified by a power law:
        	radial velocity = vrad(1)*(r/radius(1))**vrad(2)
        Default=0,0. If only one value given then vrad = vrad(1)
        Units are km/s.

Key: vsys
        Systemic velocity of the disk. Units are km/s. Default=0.
        For options=rms, vsys is a constant rms along the line of sight.

Key: z
        Thickness of disk, and power law: z' = z(1)*(r/radius(1))**z(2)
        Default=0,0. If only one value given then z' = z(1)
        The units of z(1) are the same as arcsec along major axis of disk.

Key: out
        The output image. No default.

Key: options
        rms	The output image is the rms calculated from vsys and
        	the rms velocity along the line of sight, computed by
        	integrating through the disk thickness given by z.
        sample	The rotation velocity is specified by values vrot
        	sampled at the radius values. Default is power law.