Oleg M. Smirnov, Oleg Malkov (Institute of Astronomy, Russian Academy of Sciences)
XSKYMAP, an IDL widgets application, was originally developed as a graphical interface to the ZGSC catalog (Smirnov & Malkov, ADASS VI). ZGSC is a compressed version of the Guide Star Catalog, employing a binary format and an adaptive compression algorithm to achieve 6:1 lossless compression of the GSC - down to 200Mb, from 1.2Gb (Smirnov & Malkov, ADASS V). Since then, XSKYMAP has grown into a powerful sky catalog visualisation tool. Besides facilitating on-the-fly decompression and data retrieval (with support for four coordinate systems), XSKYMAP also provides mouse-based catalog feedback, i.e., objects may be selected with the mouse, directly on the map, to view their corresponding full catalog entries. The software also provides mouse operations for zoom in/out and recentering of region, click-and-drag for computing angular separation and positional angles, and tracking of mouse coordinates with dynamic display of sky coordinates and separation/positional angle relative to center of area. The user can interactively change the map legend (i.e., symbol and color used for each type of object), and selectively display and label particular types of objects. XSKYMAP uses a custom map projection routine, one which allows accurate plotting of truly rectangular areas even in polar regions, and supports arbitrary rotation of the map relative to North on the sky.
XSKYMAP has also been integrated with the control software for the Galileo telescope (Pasian et al., ADASS VII). In the process it has aquired the capability display 2D images (e.g., directly from the instrument), and overplot the catalog map on top. Hard copy output in PostScript format is also provided, both in map-only mode, and in image+map overplot mode.
Recently, XSKYMAP has been extended to support other astronomical catalogs. An open catalog query interface has been implemented; more catalogs may be attached by adding appropriate query modules. Queries over several catalogs may be performed simultaneously, with the results plotted over the same field. An example of this is the PPM astrometric catalog (source of most precise proper motions to date). Thus, GSC's inherent depth of field is supplemented by very precise positions from the PPM. A query module for the new USNO-A catalog is under development.