Three-Dimensional Data Visualization in SAOImage DS9 Version 7

Tracy L. Beck, tbeck@stsci.edu, & William Joye, wjoye@cfa.harvard.edu

The Smithsonian Astrophysical Observatory released version 7 of the popular data-viewing tool SAOImage DS9 in June 2012. SAOImage DS9 is a stand-alone application for imaging and data visualization. The new version supports 3-D viewing of astronomical data cubes, which will be of great interest to the astronomical community. These days, more and more data products, in widely ranging areas of science, are in the format of 3-D data cubes. The information in such data cubes may be radio data, integral field spectroscopy, or a time series of multiple two-dimensional (2-D) images. Whatever the application, the need for new visualization tools for such complex datasets has never been greater, and the new version of SAOImage DS9 is most welcome.

In previous versions of SAOImage DS9, 3-D datacubes could be loaded into traditional 2-D image frames, and users could then step through successive z-dimension pixel slices of the data cube. New functionality in SAOImage DS9 v.7 allows users to work with the 3-D data regions in the 2-D display view. This permits simultaneous viewing of a collapsed 1-D spectrum through the data cube (see Figure 1). Users can interact with the 1-D spectra by zooming in and out on features in the plotting window.

To further visualize 3-D data in SAOImage DS9 v.7, a new “Frame 3D” module allows users to view data cubes in multiple dimensions by rotation in azimuth and elevation. The result is improved data interaction at different orientations (see Figure 2). Frame 3D implements a simple ray-trace algorithm. For each pixel on the screen, a ray is projected back into the view volume, based on the current viewing parameters, and returns a data value if the ray intersects the data cube. The time it takes to render depends on the zoom factor and on how many rays are needed to project the data cube onto the screen in the view volume. Frame 3D works on all hardware platforms currently supported by DS9, including 32-bit and 64-bit versions of Linux and MacOSX, and 32-bit versions of Windows and Solaris.

In the new 3-D frame of SAOImage DS9, all of the previous 2-D graphics, regions, cross hairs, contours, and coordinate grids are available, and they are applied to the current slice as selected by the user. The user can also crop the data cube for all three axes to view just a sub-region of the data. Moreover, the option exists to create mpeg movies from 3-D astronomical data sets, either by stepping through the third dimension in a 2-D view, or by rotating the data cube in azimuth or elevation. The user may generate 3-D images in PostScript, jpeg, tiff, and other printable formats, just as in the 2-D case. Analysis macros for SAOImage DS9 have been enhanced to fully support the new 3-D module, allowing the user to invoke external analysis tasks for the current view parameters and to return results back into SAOImage DS9 in the form of text, plot, 2-D image, or 3-D image.

Funding for 3-D data visualization in SAOImage DS9 was provided by the Webb mission office at the Institute.

References

Storchi-Bergmann, T., McGregor, P. J., Riffel, Rogemar A., Simões Lopes, R., Beck, T., & Dopita, M. 2009, “Feeding versus feedback in NGC 4151 probed with Gemini NIFS – I. Excitation,” MNRAS, 394, 1148

Storchi-Bergmann, T., Simões Lopes, R. D., McGregor, P. J., Riffel, Rogemar A., Beck, T., & Martini, P.  2010, “Feeding versus feedback in NGC 4151 probed with Gemini NIFS – II. Kinematics,” MNRAS, 402, 819