Documentation on velimage

Task: velimage
Purpose: Make (x,y,z) image from an (x,y) image and model z-values.
Categories: image analysis

       VELIMAGE is a MIRIAD task to make an (x,y,z) image from an (x,y)
        image and a model for the z-values and dispersion. The z-values,
        for example the mean velocity, are input as an (x,y) image, whilst
        the dispersion can be input as either an (x,y) image or a fixed
        value. The output image is formed as:-

           out(x,y,z) = in1(x,y) * exp(-(z-in2(x,y))**2/(2*sigma**2)))

        VELIMAGE can be used to compare models with the data. For example
        one can generate a model image corresponding to a rotating galaxy,
        convolve it with the actual beam and subtract the model from the
        data to determine if there is residual emission which deviates from
        the model rotation curve.

Key: in
       The input image names, separated by commas. The first image is the
        (x,y) intensity distribution integrated over the z-axis. No default.
       e.g. velocity-integrated image. The second image is an (x,y) model
        for the z-values, e.g. a mean velocity image. No default.
       A 3rd input image gives the z-dispersion at each point. e.g. a
        velocity dispersion image. If the 3rd image is not specified then
        fixed dispersion, sigma must be specified. 

Key: region
        Region of image to be used. The default region is the entire image.
        See documentation on region for details. All pixels within the
        bounding box are used; pixel masking is not used.

Key: sigma
        Fixed value for z-dispersion if not specified by 3rd input image.

Key: nchan
        Number of channels for z-axis of output image. Default=1.

Key: start
        Starting value for z-axis of output image. No default.

Key: step
        Interval for z-axis of output image. No default.

Key: out
       The output (x,y,z) image. No default.

Key: options
        Options. Minimum match is active.
          relax  ignore axis descriptor mismatches
                 (e.g. pixel increments etc).  Use with care.