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Subsections

• Definition
• Functionality
• AIPS++ Integration

User Requirements

Definition

The definition of the requirements that astronomers have for visualization and analysis of astronomical images has been obtained from the user requirements documents prepared by members of the AIPS++ consortium, from meetings at which astronomical visualization needs have been discussed and tools have been demonstrated, from comments on earlier descriptions of AipsView, and from feedback provided by a number of astronomers. The definition of requirements will continue throughout the development process. We have made very substantial changes in earlier designs and preliminary implementations in response to such feedback, and expect this process to accelerate with the alpha release of AipsView, planned for early 1995.

Functionality

We list below the functionality that we expect to implement in AipsView. Items with a filled bullet ($\bullet$) will be functional in the alpha release of AipsView planned for early 1995. Items preceded by an open bullet (o) are planned for future releases.

Two-dimensional (2D) display

• Easy to use, intuitive user interface.

• Input of FITS image files.

• Display of 2D images.

• Display of any orthogonal 2D slice from a 3D image cube (e.g., display of RA vs. Dec for a given velocity, display of RA vs. velocity for a fixed Dec, etc.).

• Movie or animation function for time-sequence display of third dimension of 3D images.

• Blink function for animation display of 2 (or more) single planes of different images.

• Simultaneous display of images from multiple data sets.

• Panning and zooming.

• Interactive display of data values, pixel values, and world (e.g., RA, Dec) coordinate values as pointer is moved around image.

• Interactive vector (line drawing) plots of data value vs. coordinate value, e.g., for line profile plots or intensity vs. spatial position plots.

• Hard copy output as X Window screen dump.

• Complete colormap editor for manipulation of color look-up tables and creation of new tables.

• Input of AIPS++ internal format images and HDF files.

• Tile (mosaic) display of multiple planes of a single image cube.

• Synchronization of multiple images, so operations carried out on 1 image may automatically be carried out on the others.

• Support for image blanking, with upper and lower threshold blanking determined by values in the image or in a second image. Blanking or threshold values adjustable via a parameter or slider.

• Multiple-dimension region selection, with regions being either single points, rectangular regions, simple geometric shapes, polygonal regions, free-hand regions, or boundary selection (along an image contour, for example).

• Hard copy output as postscript files with full resolution.

• Support for 24-bit displays, with color values determined from 3 separate 2D regions, either from 3 planes (e.g., different velocities) of 3D images or from 3 separate images.

• Re-binning and re-registration of images, so that multiple images may be displayed on a common coordinate system.

• Support for handling very large data sets. This will include easy display of subregions with full resolution and/or subsampled images.

• Full support for vector graphics, for plotting line profiles, contours, annotations, etc.

• Full support for AIPS++ image analysis, with tasks being called from AipsView and results reported back to AipsView.

Three-dimensional (3D) display

3D applications are very CPU and/or graphics processor intensive, and cannot realistically be supported on the typical low-end workstations. Use of 3D visualization techniques in astronomy is a largely unexplored area, and part of our work will be to discover what algorithms are useful and how they may best be implemented. For these reasons, we plan to develop 3D functions in the OpenGL and OpenInventor environments on SGI workstations. This will not necessarily leave out those without SGI workstations, for OpenGL and OpenInventor have been licensed by third party companies for Sun workstations, and by HP, IBM, and Microsoft. Exactly how 3D visualization will be supported by AIPS++ will be an evolving topic, subject to developments in workstation hardware and software and astronomer requirements and demands. The 3D visualization tool will include the functionality of the 2D tool, plus the items listed below.

• Isosurface representation. The 3D analog of a 2D contour plot, an isosurface shows the surface of constant value within a 3D volume.

• Block and brick excavation. These techniques support removal of user-specified subvolumes, revealing the data values in the neighboring data cells.

• Direct volume rendering. A variety of techniques determine image pixel values by casting rays through the data volume. We will explore both software approaches and interactive, hardware-based approaches.

• Volume subregion selection. In addition to rectangular region selection, irregular subregions can be selected using deformable containers, such as "rubber sheets".

AIPS++ Integration

It was originally planned that there be only a single AIPS++ visualization development effort, with the display classes developed for AipsView being used to support infrastructure visualization needs. Recently, AIPS++ project management decided to separate infrastructure visualization from the high-end visualization tool described here. The primary reason for this decision was to have the crucial infrastructure visualization needs of AIPS++ under the control of the infrastructure development group at Charlottesville, so that problems of distributed development of code that must be tightly integrated would be avoided. At the same time, development of code that need not be tightly integrated with the infrastructure and which was not being written at Charlottesville would be freed from the unavoidable overhead and inefficiency of distributed code development. This approach loosens the requirement for full integration of the AipsView tool with AIPS++ which has the advantage of allowing greater flexibility in the development of AipsView. We expect that this flexibility will permit the development of a more complete and powerful tool.