Copyright © Michael Richmond.
This work is licensed under a Creative Commons License.
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XVista is a collection of programs that run on UNIX machines under X-windows for the display and reduction of astronomical images. It has evolved from PCVISTA (Treffers and Richmond, Pub. Astr. Soc. Pac. 101, pp. 725-730) which was in turn designed to be a somewhat compatible subset of the VISTA program developed at U.C. Santa Cruz and Berkeley for the reduction of CCD data.
The description of the XVista commands can be found in files with the extension ".man". The contents of these files can be accessed online by using the man command. Hardcopy can be generated by the following command:
troff -man xxx.man | lpr -t
where the desired command should be substituted for xxx.
Keywords in square brackets [ ] are optional. Keywords which are followed by an ``='' sign imply that a numerical (or symbol ) value must be entered. Caution: no spaces can be imbedded between the keyword, the equal sign and the value.
Commands can be divided into the following categories:
image arithmetic add add images sub subtract images mul multiply images div divide images addvec add a 1-D vector to a 2-D image subvec subtract a 1-D vector from a 2-D image mulvec multiply a 2-D image by a 1-D vector divvec divide a 2-D image by a 1-D vector data display tv display grey scale image on screen cursor displays data values at cursor position marks displays cross hairs on a image pfits prints out image data on the screen image marking box defines a rectangular image subsection circle defines a circular image subsection image statistics abx calculates miscellaneous statistics axes calculates centroid of images hist computes histograms mn computes mean of images profile makes a circular profile around a centroid sky computes sky level processing back fits low-order polynomial to image and subtracts it bin squashes an image clip replaces pixels outside a specified intensity range flip changes orientation of image imshift shifts image in rows and columns makevec creates a 1-D vector from a 2-D image mash generates spectra from image files into ASCII file median creates median frame from several images ring convolve images with a user-supplied kernal rotate rotates images rowcol cuts rows or columns from data into an ASCII file sbig2fits convert an SBIG "uncompressed" image to FITS format smooth convolves images with one of several standard functions window cuts down images header manipulation buffers displays the FITS header variables comment enters in comments into the FITS header miscellaneous convert convert bitmaps into FITS-format files impatch replaces pixel values in an image implant inserts an image into another image (montage) xlet sets and inspect variables makeim converts ascii to FITS-format files propinit initializes X window properties pstar generates artificial star images xplot plot program for columnar data photometry stars finds stars in an image phot performs aperture photometry mask creates a file describing defects in the image
XVista uses variables to carry data such as sky brightness or pixel locations from one program to another. Variables may be substituted for any numerical input data. In addition any arithmetic combination of variables can be used.
The xlet command allows users to set the values of symbols and to inspect their values.
The allowed arithmetic operators are +,-,*,/ as well as the elementary trigonometric and exponential functions: sin, cos, tan, sqrt, exp, log, log10. Parentheses are allowed; however, no spaces may be included in any arithmetic statement. For example, in the axes command the value of sky could be set by "sky=4.5*sin(blotz)", where blotz was a preset variable. Note: the entire group was set in quotes to hide the * operator from the UNIX shell.
Some programs set the values of the XVista variables. For example:
mn_fname the mean of the file "fname"
sky the "sky" value
axr, axc the center row and columns found by AXES
box# the location of the boxes
circle# the location of the circles
profile_boxrad size of box used to calc radial profile
of displayed image
profile_fitrad radius out to which to fit gaussian
to selected star
aperture_innersky inner radius of sky annulus for photometry
of displayed image
aperture_outersky outer radius of sky annulus for photometry
of displayed image
aperture_radius outer radius of aperture for photometry
of displayed image
aperture_magzero zero point of flux->magnitude conversion
The XVista variables are stored in a file referred to hereafter as the ``symbol table''; it is a small ASCII text file. The name and path of this file must be set by the environment vaiable SYM_TABLE.
The image data are stored in disk files in FITS format, a commonly used method of storing multi-dimensional data containing header information. A description of the standard is given in Wells, Greisen, and Harten, Astron. and Astrophys. Suppl. Ser, 44, 363 (1981).
The header contains information about the number of axes (always 2), the numbers of rows and columns (NAXIS2 and NAXIS1 respectively) and the word size (always 16 bits in this suite of programs). Note that the XVista FITS-reading routines understand ONLY 16-bit integer FITS files at this time. Although FITS header variables such as the time and date of the observation and the exposure time may be present, XVista makes little use of the header data, and except for window and bin, does not modify the header. The header can be inspected by using the buffers command.
The data files usually have the three letter extension '.fts'. This extension will often be added by XVista commands and need not be typed in explicitly. You can read files with different extensions by typing them explicitly.
Although internally most of the arithmetic is done as 32 bit integers, the data are written as as 16 bit integers. The data are treated as "signed" quantities ranging from +32767 to -32768. If two data files with pixel values in the neighborhood of 20000 are added together (without the NORM switch), the data will "overflow" into negative numbers.
The FITS reader is capable of reading data with BSCALE and BZERO values, however, many of the commands will only write data with BSCALE=1.0 and BZERO=0. and so truncation may occur.
To compile XVista we recommend you copy the compressed archive file into a separate directory (Xvista). Then run the following UNIX commands:
uncompress XvistaN.a ar x XvistaN.a make
Where N is the version number of Xvista. If all goes well you should create all the executable programs. To invoke thes programs from other directories you will have to modify your PATH. In addition you should modify your .login file to set up the symbol table. For example:
setenv SYM_TABLE ~/SYM_TABLE rm $SYM_TABLE # clears values from previous sessions
The tv program communicates to other program by X-window properties. For them to work properly you must place the propinit command into the routine which is called on the startup of X Windows. On a Sun running open windows we place it in the file ~/.openwin-init.
For the manual pages to work we go thru a rather arcane procedure of setting up a separate subdirectory 'man1' below the Xvista directory and placing all the .man files with their extension replaced with .1 (yes, the number 1) into it. And placing the following line into the .login file
setenv MANPATH ~/Xvista:/usr/man
The exact details of this command will vary from user to user, try to read the UNIX man page on man.
You will also have to modify the makefile to specify the exact path for the file 'xplot.help'.
Copyright © Michael Richmond.
This work is licensed under a Creative Commons License.