This shell script uses a velocity map of a spatial region to create a new velocity map. The spatial co-ordinates and velocity value at each pixel specify the co-ordinates of voxels in a spectral cube. The data value in the cube at this voxel becomes the data value in the output map.

While creating velocity maps is the expected usage for the script, it makes no specific tests that the $Z$ co-ordinate is velocity, or even that the image value is velocity. In mathematical form the output image values are given by the following expression.

One application is multi-spectral imaging in complex molecular clouds, where one optically thin spectral line provides a clearer mapping of the cloud and system velocities. Using this specie’s velocity map traces the varying velocity, and thus data observed through different spectral lines can be compared, enabling the calculation of cloud parameters such as opacity.

• -i filename
  A three-dimensional NDF with spatial axes and a third velocity axis By default the script will prompt for the input cube.

• -mfilename
  The name of a two-dimensional velocity map, where the data values are velocities. It should have the same spatial co-ordinates as the supplied cube. Such a map can be created using velmap or KAPPA:COLLAPSE with the Iwc or Comax estimators. By default the script will prompt for the input cube.

• -ofilename
  The filename for the output NDF velocity map.

• The script assumes $X$ and $Y$ axes are spatial and $Z$ is spectral. Use KAPPA:PERMAXES to re-orient the cube if that is not the case.

• A further assumption is the cube’s $Z$-axis co-ordinate matches the data values in the supplied image. If that is not the case, change the co-ordinate system with KAPPA:WCSFRAME and/or KAPPA:WCSATTRIB.

• It propagates the original variances from the cube, but does not account for errors in the input velocity map affecting the values extracted from the cube.

This script invokes a collection of A-tasks from the Kappa package.