Viewer Summary

The CASA viewer is one of two primary visualization tools in CASA. It displays image cubes and measurement sets as two dimentional raster images. It is the third in a series of visualization tools whose development spans nearly a quarter century. The initial viewer developed at NCSA provided a capable prototype for the subsequent two viewers which were developed internally by the CASA project. During this time the design emphasis has shifted from an integrated tool, to a toolkit for visualization applications, and back to an integrated tool.

The viewer is sometimes used on collected data at the beginning of the data reduction process to flagg bad data in measurement sets. The bad data occurrs due to radio interference or instrument effects. The viewer is used to create a pseudo-color raster image of individual channels from the collected data. The pseudo-color is useful because it allows for identifing outliers and systematic or intermittent effects in what may be a very large data set.

At the conclusion of data reduction the viewer is used to create pseudo-color maps of the final images of the radio sources. Each channel in the image cube corresponds to a frequency, and the frequencies can in turn be interpreted as representation of the velocity of different areas of the source. Another way of looking at the image cube is as a two dimensional array of spectra from the source, and the viewer has a number of integrated tools which allow these spectra to be plotted. Standard spectra for different molecules can be overlaid to help identify the chemical composition of the source. In a similar vein, arbitrary two dimensional slices can taken through the image cube. When viewed as representing spectral velocities, these two dimensional cuts can help discern the motion of the radio source, typically galactic motion. Underlying all image cube operations is the ability to accurately label and align multiple datasets, e.g. overlaying one image cube displayed as a contour on a second image cube displayed as a pseudo-color raster. The labeling scale covers entire range from a narrow field of view to a very wide field of view. To support axis labeling of a wide field of view, the CASA viewer includes support for curvilinear coordinates in axis labeling***.

The viewer supports the CASA data reduction process at the intial steps, at the final steps, and at certain interpediate steps. For many, it is the graphical face of CASA, and its tools are used to glean insight into the final images through graphical and statistical means.

*** footnote: include reference to wcslib web page (wcslib reference should be included because it is the basis for axis labeling in the viewer as well as the coordinate systems throughout CASA): http://www.atnf.csiro.au/people/mcalabre/WCS/wcslib/

*** we must be very careful with formatting of the URL: http://www.computer.org/portal/web/publications/style_refs

-- DarrellSchiebel - 2013-11-06