Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.adass.org/adass/proceedings/adass96/reprints/albrechtm.pdf Дата изменения: Wed Jan 14 23:03:59 1998 Дата индексирования: Tue Oct 2 15:27:29 2012 Кодировка: Поисковые слова: messenger

Astronomical Data Analysis Software and Systems VI ASP Conference Series, Vol. 125, 1997 Gareth Hunt and H. E. Payne, eds.

Access to Data Sources and the ESO SkyCat Tool
M. A. Albrecht, A. Brighton, T. Herlin, P. Biereichel European Southern Observatory D. Durand Canadian Astronomy Data Center, DAO/NRC Abstract. SkyCat is a tool that combines image visualization with access to astronomical catalogs and data archives. SkyCat uses a standardized URL syntax to access a large numb er of data sources on the net. This pap er addresses the issues that were solved in defining and implementing such standardized scheme. More information on SkyCat can b e found at the SkyCat Web site.1

1.

SkyCat Features

The ESO SkyCat Tool includes the following features: · op en and visualize a variety of FITS images including supp ort for World Coordinate System (WCS), interactive measurement of offsets, and other standard visualization functions (SAOimage-like), · overlay and edit color graphic ob jects on the image, like "tagging" sources with text, arrows, circles, or other graphic elements such as masks, · PostScript color printing of the display (image + graphics), · access and load an image from a network server of the Digitized Sky Survey scans, · access and load catalog information from a numb er of p opular astronomical catalogs, like the HST Guide Star Catalog, · access local user catalogs, · save catalog data locally, · overlay catalog sources on an image, · interact with Netscap e to display more ob ject information when available (supp ort for Mosaic may b e added in a future release),
1

http://archive.eso.org/skycat

333

© Copyright 1997 Astronomical Society of the Pacific. All rights reserved.


334

Albrecht et al. · access the observations catalog from the NTT, HST, and CFHT Science Archives, · access SIMBAD and NED, b oth as name resolvers and for information on known ob jects, · retrieve preview and other compressed images, and decompress them on the fly, · load compressed images in hcompress, gzip, or UNIX compress format, · retrieve and plot tabular preview data for a selected ob ject as an (x, y ) graph, · calculate, display, and plot the center p osition, FWHM, angle and, other information for a selected star or ob ject, · access SkyCat features from a remote process via socket interface or via Tk "send," · access image header and data (FITS format) via SysV shared memory and/or mmap, and · overlay RA/DEC grid on the image.

We are working on these additional features: (i) save canvas graphics, p ossibly as a FITS extension on the image file, (ii) user customizable symb ols to "lab el" ob jects on the canvas, (iii) interact with a WWW browser to access catalog documentation and other documents, (iv ) load lists of catalogs from sites (ESO, CADC, CDS, local) and allow user to select a preferred default catalog list, (v ) save user preferences for look-up tables and other settings, and (vi) add or edit WCS parameters for a given image. 2. The Software

SkyCat was develop ed by ESO's Data Management and Very Large Telescop e (VLT) Pro ject divisions with contributions from the Canadian Astronomical Data Center (CADC). The tool was originally conceived as a demo of the capabilities of the class library that we are developing for the VLT. This library consists so far of two ma jor subsystems: (i) The Real-time Display (RTD) image classes with the RTD widget (see The Messenger, 81, 1995), and (ii) the Catalog Interface classes with the CatSelect widget. These constitute the basic building blocks of SkyCat. Early demonstrations of the tool to users were received so enthusiastically that we decided to p olish things up, and produce the current version. 2.1. Java vs. Tcl/Tk

Some users might wonder why we did this development in the Tcl/Tk environment rather than in Java. The main reason is the pragmatic need to have the functionality implemented when the VLT comes on-line (mid-1997). However, great care has b een taken to develop as much as p ossible in the short time with ob ject oriented languages (C++, [incr Tcl]), having in mind that the future lies in tele-scripting rather than in the distribution of binary code.


Access to Data Sources and the ESO SkyCat Tool

335

Figure 1. 2.2.

SkyCat showing a DSS image of NGC1275.

Distribution and Supp ort

SkyCat is freely available to any users who want to download and use the software at their own risk. SkyCat is available as an executable for these platforms: (i) SunOS 4.1.3, (ii) HP-UX A.09.05, (iii) Solaris 2.5 (SunOS 5.5), and (iv ) HPUX B.10.10; ESO will maintain the latter two in the longer term--they are the platforms on which VLT software will run. ESO does not have the resources to p ort and maintain SkyCat on any other platforms. We will b e glad to redistribute any p ort that other p eople or groups may supp ort, but decline any resp onsibility for them. The software is also available as source code for research and other nonprofit organizations. If you are interested in obtaining the package, please send us a note. Please rep ort problems or send suggestions to malbrech@eso.org or to abrighto@eso.org. Acknowledgments. We very much appreciated practicing wishful programming at large, i.e., wishing a utility, a function, or just a code fragment that would just do that bit you badly need, then surfing the net, fetching it, and re-using it in our code. Here is an incomplete list of packages that we either par-


336

Albrecht et al.

Figure 2.

The CatSelect display of the field around NGC1275.

tially re-used or used as a source of inspiration: (i) STARCAT contributed many of its internals, (ii) Tcl/Tk, TclX, BLT and [incr tcl] give the glue around the C++ classes and widgets and Tk provides the canvas graphics, (iii) SAOimage lent the WCS lib, (iv ) GSC server provided by courtesy of A. Preite-Martinez & F. Ochsenb ein, (v ) SIMBAD and NED client routines allow name resolving, (vi) the CADC "press" library is used to inflate compressed (hcompress, gzip, ...) images, (vii) Midas routines are used to calculate the centroid p osition, FWHM, and angle of selected stars/ob jects, and (v iii) GNU Emacs routines are used to make a single binary executable from many Tcl/Tk scripts and data files. References Chavan, A. M., & Albrecht, M. A. 1997, this volume, 367