### pvslice

Extracts and displays a velocity-position slice from an (RA,Dec,vel) cube

#### Description:

This script extracts and displays a slice from a position-velocity cube. The slice need not be parallel to either spatial pixel axis.

The script displays a chosen spatial plane from the supplied cube in the left half of the current graphics device. You are then invited to select two spatial positions within the displayed plane using the cursor. A two-dimensional slice is then extracted from the cube that passes through the two selected spatial positions. The first axis in this slice measures spatial distance along the line, and the second axis is the velocity axis. This slice appears in the right-hand side of the current graphics device, and saved to the specified output NDF.

#### Usage:

pvslice -i filename -o filename [-ci index] [-p plane]

#### Command-line Arguments

• -ci index
The colour or colour index of the annotations on the left-hand display indicating the spatial location of the slice. An index should be a positive integer no more than 15, normally 2 or 3 to stand out from other elements of the plot. If absent the annotations will appear in red. []
• -ifilename
The name of an existing three-dimensional (RA,Dec,vel) cube. The script will prompt for the input file if not supplied on the command line.

• -ofilename
The name of the NDF in which to store the velocity-position slice. The script will prompt for this NDF if it is not supplied via this option.

• -pplane
Velocity or pixel index of the plane to display to enable cursor selection of the slice end points. To specify a velocity supply a floating-point value such as 2.0; for an index supply an integer. [0]

#### Examples:

This extracts a user-selected plane from the cube NDF called orion_masked, and saves it to NDF orion_pvmap. The slice is shown to the right of the spatial image.
pvslice -i orion_masked -o orion_pvmap -p 1.5
As above but slice selection is from the velocity plane at 1.5 as opposed to the middle index.

#### Notes:

• The WCS in the returned NDF is somewhat complex; it has a degenerate pixel axis and a degenerate WCS axis. These could be removed using ndfcopy trim, but this would result in a WCS with no inverse transformation (from current to pixel), which gives problems when displaying it, etc. Alternatively, the AXIS frame can be used by doing wcsframe frame=axis.

• To avoid modification of the input cube, the script creates a temporary copy in the current directory, and deletes the copy upon completion.

• While the script is intended to make position-velocity slices from spectral cubes, the contents of the third axis is arbitrary.

• The script clears the graphics database for the current device. It then creates two FRAME pictures with labels a1 and a2. Within each of these DISPLAY creates FRAME and DATA pictures, the former holding annotated axes. On exit a2 is the current picture.

• The label for the spatial (first) axis in the slice plot is "Offset from start".

#### Implementation Status:

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