Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://hea-www.harvard.edu/RD/saotng/xpaapp.ps.Z Äàòà èçìåíåíèÿ: Thu Jul 3 18:59:01 1997 Äàòà èíäåêñèðîâàíèÿ: Fri Dec 21 23:12:16 2007 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: spitzer space telescope

Applying Public Access Programming Techniques To
SAOimage
E. Mandel
Smithsonian Astrophysical Observatory, Cambridge, MA 02138
D. Tody
National Optical Astronomy Observatories, Tucson, AZ 85719
Abstract.
This paper describes our application of the X Public Access (XPA)
interface to the new version of SAOimage. XPA allows an Xt program
to define named public access points through which data and commands
can be exchanged with external programs. It makes possible the external
control of the program's main functions, including image display, image
zoom and pan, color map manipulation, cursor/region definition, and
frame selection. It also supports ``externalization'' of internal algorithms
such as file access and scaling. Finally, we describe how XPA is used
to support user­configurable ``quick­look'' analysis of image data and bi­
directional communication with other processes.
1. Introduction
Astronomical software development needs to adopt more ``open systems'' con­
cepts and designs. Users increasingly want to extend existing software and to
combine tasks from different systems in order to create their own heterogeneous
research environments. Our software designs must reflect this increasing need
for flexibility and extensibility without sacrificing functionality and without vi­
olating budget constraints.
The SAOimage display program has been very popular with astronomers
over the past decade. In the age of ``open systems'', it needs updating to support
extensible features such as:
ffl an easy way to display arbitrary data file formats.
ffl an easy way to control image display from an external process.
ffl an easy way to integrate analysis routines into the image display.
In order to update SAOimage efficiently and cost­effectively, SAO and
NOAO will collaborate to develop a high­quality image display program, bas­
ing our work on the ximtool program developed by D. Tody for IRAF. Ximtool
uses the NOAO widget server and gterm­image widget to support customized
graphical user interfaces (GUIs), image and line graphics, multiple frame buffers,
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user­defined color maps, region markers, etc. It provides a high­level image dis­
play programming interface as well as low­level access to gterm­image widget
functions. Our aim is to layer ``open­ended'' functionality on top of ximtool
in order to develop SAOtng (SAOimage: The Next Generation). In this way,
SAO and NOAO can share development of image display, while satisfying our
individual needs.
2. The X Public Access Mechanism
To add ``open systems'' features to SAOtng, we will utilize the X Public Ac­
cess mechanism (XPA), described in Mandel and Swick, 1994. XPA allows an
Xt program to define named points of public access, through which data and
commands can be communicated to/from external programs:
SAOtng
command line
program
XPA names are used to define public access
The xpaget program receives data and info
The xpaset program sends
The OpenXPA subroutine allows standard I/O
routines to exchange data and info with SAOtng
from SAOtng
data and commands to SAOtng
points for SAOtng commands and data
Figure 1: We have used XPA to extend the ximtool image server into an open­ended
SAOtng display service that can cooperate with other processes and programs.
3. Controlling SAOtng
The standard SAOtng graphical user interface is a simple menu­based GUI that
parallels the original SAOimage menu/command paradigm. It provides menus
for image and frame selection, scaling, color maps, zoom/pan, regions, etc. All
of these menu functions also are defined to be XPA public access points. Thus,
SAOtng can be controlled directly through its menu­based GUI or externally
through the XPA mechanism (see Figure 2).
For example, the xpaset program can be used to change SAOtng's scaling
algorithm and the xpaget program can be used to retrieve the current scale:
csh? echo ''scale log'' --- xpaset SAOtng
csh? xpaget SAOtng scale
log
In fact, the SAOtng GUI uses XPA to send commands to itself. This imple­
mentation ensures that support for external control of SAOtng does not lag
behind the internally­supported user interface: the GUI behaves as if it were
just another external process!
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4. External Support For File Access
A FITS file can be sent directly to SAOtng for display using XPA:
cat foo.fits --- xpaset SAOtng
Other file formats are supported by writing 2 file access programs:
ffl a header access program to generate a FITS header of the full image.
ffl a data access program to generate a FITS image of a specified data section
(given the center, dimensions, and block factor).
These access programs are specified at start­up time using ASCII files. To load
an image, the programs are run externally (using the system() subroutine) to
create FITS­format data for a specified data section, which are passed back to
SAOtng for display using XPA:
ffl When a new file name is sent to SAOtng, the appropriate header access
program is run to gather the overall image dimensions.
ffl The data access program is run to extract the desired image section, which
then is scaled to 8 bits and displayed.
ffl The data access program again extracts the data section and stores it as
raw data for later use (e.g., re­scaling the image).
Note that adding new formats does not require re­compilation of SAOtng.
5. Integration of Analysis Routines
Each file type can have user­defined analysis commands associated with it. These
analysis commands are defined at start­up time by means of ASCII descriptions.
The analysis commands associated with the currently displayed image are avail­
able for execution via an analysis menu. When selected from this menu, an
analysis command is macro­expanded and then executed externally. Results
can be displayed in a separate window or even can be sent back to SAOtng, i.e.,
a command can create an image and then send it to SAOtng for display:
$data --- smooth ... --- xpaset SAOtng ''frame new''
In the example above, the ``$data'' macro is expanded into an XPA command
that retrieves the FITS representation of the displayed image. The FITS image
generated by the smooth program is piped into a new frame buffer of SAOtng.
6. Cooperation With Other Processes
XPA allows the re­use of GUI programs so that new systems can be built from
existing high­level components. For example, the SAOtng ``Load Image'' menu
option pops up the XDir program, a directory and file browser that also offers
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XPA services (see Figure 2). The XDir program then can be used to browse
through directory trees using template filters. Double clicking on an image file
causes XDir to send an XPA command to SAOtng to load the new image. Thus,
SAOtng can make use of XDir's sophisticated capabilities without linking them
explicitly: GUI programs can be re­used in the same manner as subroutines!
Figure 2: SAOtng has a simple menu­based GUI. It can be commanded externally
(lower right) and can communicate with programs such as XDir (upper right).
7. Conclusion
SAOtng exemplifies a new type of astronomical analysis program that is exten­
sible and that cooperates with other processes. It takes us closer to an era in
which our heterogeneous analysis systems can work as an integrated whole.
Acknowledgments. This work was supported under NASA contracts to
the IRAF Technical Working Group (NAGW­1921), the AXAF High Resolution
Camera (NAS8­38248), and the AXAF Science Center (NAS8­39073).
References
Mandel, E. and Swick, R. 1994, PASP, 96, 198
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