man gcx (1): astronomical image processing and photometry

SYNOPSIS

gcx [options] [files...]

DESCRIPTION

gcx is an astronomical image processing and data reduction tool, with an easy to use graphical user interface. It provides a complete set of data reduction functions for CCD photometry, with frame WCS fitting, automatic star identification, aperture photometry of target and standard stars, single-frame ensemble photometry solution finding, multi-frame color coefficient fitting, extinction coefficient fitting, and all-sky photometry, as well as general-purpose astronomical image processing functions (bias, dark, flat, frame alignment and stacking); It can function as a FITS viewer.

For automating data reduction of large numbers of frames, gcx implements recipe files. These files contain specific information about the objects measured in each field. Once a recipe file is created for a given field, any number of frames of that field can be reduced without user intervention.

The program can control CCD cameras and telescopes, and implement automatic observation scripting. Cameras are controlled through a hardware-specific server, to which gcx connects through a TCP socket. It generates FITS files with comprehensive header information.

Telescopes and mounts using the LX200 protocol are supported. gcx uses it's automatic field identification functions to refine telecope pointing accuracy.

OPTIONS

When invoked without arguments, the program runs in GUI mode. Most functions are also accessible through command line options, descibed below.

-h, --help: Print command line options.
--help-all: Print all the on-line help on stdout.
--version: Print program version.
-D, --debug <level>: Set debug level to <level>; 0=quiet, 4=noisy.
-o, --output <file_name>: Set output file name for import, convert and frame operations.
-r, --rcfile <config_file>: Load configuration file.
-S, --set <option>=<value>: Set the value of an option overriding the configuration file.
-i, --interactive: Force display frames as they are being processed.

Observation Scripting, Photometry and File Conversion Options

-p, --recipe <recipe_file>: Load recipe file (searches rcp_path).
-P, --phot-run <recipe_file>: Load recipe file and run photometry in batch mode. Report in native format.
-V, --phot-run-aavso <recipe_file>: Load recipe file and run photometry in batch mode. Report in AAVSO format.

If <recipe_file> is set to one of the following three special tokens, the recipe will change depeding on information in the frame header:

_TYHCO_: will create a recipe on-the-fly from Tycho catalog data (if available);
_OBJECT_: will search the recipe path for a file with the same name as the object in the frame (ending in .rcp);
_AUTO_: will search for a recipe by object name, and if that is not found, create a tycho one.
--import <catalog name>: Convert a tabular catalog file to the gcx Lisp-like format. Reads stdin. Current table formats are: gcvs, gcvs-pos, landolt, henden, sumner.
--merge <recipe_file>: Merge a new recipe file over the one loaded with the --recipe option. Checks are made for either positional or name duplicates. Only stars brighter than mag_limit are merged.
--set-target: Specify a target object to be merged into a recipe file. It will also set the recipe object, ra and dec fields.
--make-tycho-rcp <radius>: Create a recipe file for the object specified with --object using tycho2 stars in a box radius arcminutes around the object.
--rcp-to-aavso <recipe_file>: Convert a recipe file to the aavso db (tab-delimited) format. If the file argument is '-', stdin is read. The recipe comment and star comment fields are interpreted to get some db fields. See the --help-all output for more info.
-T, --rep-to-table <report_file>: Convert a report file to tabular format. If an output file name is not specified (with the '-o' argument), stdout is used. If the file argument is '-', stdin is read. The format of the table is specified by the value of the .file.tab_format option, see below.
-O, --obsfile <obs_file>: Load/run observation scripting file (searches obs_path).
-n, --to-pnm: Convert a fits file to 8-bit pnm. If an output file name is not specified (with the '-o' argument), stdout is used.
-j, --object: Specify a target object (useful for setting an initial wcs when there isn't enough information present in the fits headers).
--mag-limit: Set a magnitude limit for the output of import and merge commands.

CCD Reduction Options

-d, --dark <dark_frame>: Set the dark frame / do dark subtraction.
-b, --bias <bias_frame>: Set the bias frame / do bias subtraction.
-f, --flat <flat_frame>: Set the flat field frame / flatfield.
-G, --gaussian-blur <fwhm>: Set blur FWHM / apply Gaussian blur.
-a, --align <align_ref_frame>: Set the alignment reference frame / align frames.
-A, --add-bias <bias>: Set the value of a constant bias to add to all frames / add a bias to frames.
-M, --multiply <multiplier>: Set a constant to multiply all frames with / multiply frames by a scalar.

Multiplication is performed before addition.

-u, --update-file: Save reduction results overwriting the original files.
-s, --stack: Stack the frames using the method set in the configration file; for some methods additive background alignment is performed.
-F, --superflat: Stack the frames using an multiplicative background alignment procedure; the frames should be already dark-substracted.
-N, --no-reduce: Do not run the reduction operations, just load the frame list / reduction options.

When any of the CCD reduction options is set and the -i flag is not specified, the reduction operations are run in batch mode on all the supplied fits files. When no output file is specified or -i is set, the files are loaded into the batch processing file list, the reduction options set in the dialog, and the program starts up in gui mode

Report Converter Format String

The report converter option converts the native gcx output to a fixed-width tabular format that is easy to import in other programs for further processing. The table's format is defined by the .file.tab_format configuration option. The option string consists of tokens separated by spaces. There are two types of tokens: option tokens, and column tokens.

Options tokens set global table options when present. They can appear anywhere in the format string.

tablehead: Generate a table header line containing the column titles.
collist: Generate a list of columns with position information at the start of the output.
res_stats: Generate a line with descriptive statistics on the stars' residuals at the end of each frame.

Column tokens specify what information gets output in each column. The first column token corresponds to the first output column, and so on in order. Each column token can optionally be followed by a specifier of the form: width.precision. The width excludes a single character spacer between the columns. Supported colum tokens are:

name [w]: Output the star's designator.
ra [w]: Output the right ascension in h:m:s format.
dra [w.p]: Output the right ascension in decimal degrees format.
dec [w]: Output the declination in d:m:s format.
ddec [w.p]: Output the declination in decimal degrees format.
smag [w.p] <band>: Output the standard magnitude with the given name.
serr [w.p] <band>: Output the error of the standard magnitude with the given name.
imag [w.p] <band>: Output the instrumental magnitude with the given name.
ierr [w.p] <band>: Output the error of the instrumental magnitude with the given name.
flags [w]: Output reduction flags and the star type.
observation [w]: Output the name of the observation (a synthetic name that can be used to group stars reduced from the same frame.
airmass [w.p]: Output the airmass of the observation.
jdate [w.p]: Output the Julian date of the observation.
mjd [w.p]: Output the modified Julian date of the observation.
filter [w]: Output the filter name used for the observation.
xc/yc [w.p]: Output the frame coordintes of the star's centroid.
xerr/yerr [w.p]: Output the estimated centroiding errors.
dx/dy [w.p]: Output the amount the star was moved from it's catalog position when the measuring aperture was centered.
residual [w.p]: Output the star's residual in the ensemble solution.
stderr [w.p]: Output the star's standard error (residual divided by the estimated error).

Fields for which data is not available are left blank.

Image Navigation and Object Selection

Middle click or space bar: Pan cursor.
'=': Zoom in around cursor.
'-': Zoom out.
Left button drag left/right: Adjust brightness.
Left button drag up/down: Adjust contrast,
0: Auto scale intensity.
9: Scale Min-Max.
1-8: Auto scale with different intensity spans 1 is sharpest, 8 is dullest.
Left click on an object: Select object (and deselect all others).
Shift-left click on an object: Add to selection.
Ctrl-left click on a star image: Mark star (if not too faint).
Left click on image: Show local image statistics.
Right click on image: Pop-up the main menu.
Right click on an object: Pop-up the star menu.

Many useful commands have keyboard accelerators; they are displayed in the menus.

FILES

The native image file format of gcx is FITS. The program will read 16-bit integer and 32-bit float files (BITPIX = 16 or BITPIX = -32), and save 16-bit integer files. The internal representation of images is in 32-bit floating point.

gcx supports transparent compression and decompression of fits files when zcat and gzip are available and their path is set in the corresponding options.

Configuration options are stored in ~/.gcxrc. The options can be edited in GUI mode, or directly in the file itself. A template configuration file can be created by selecting "save" in the option editing dialog.

The program reads several object catalog formats. See the relevant chapter in the User's manual for information on how to set up catalogs. Catalogs are normally placed under /usr/share/gcx/catalogs.

Documentation files usually reside in the "docs" directory of the source distribution or in /usr/share/doc/gcx.

Example data is distributed separately from the main source. When installed from a package it usually goes to /usr/share/doc/gcx/examples.

AUTHOR

gcx was written by Radu Corlan, with valuable contributions from Alexandru Dan Corlan (Tycho2 searching, porting of GSC searching code); Liam Girdwood (various routines from the libnova library); Pertti Paakkonen (GUI improvements). The star search algorithm is similar to (and inspired by) the one in Elwood Downey's XEphem. WCS conversion routines are taked from classic AIPS. The GSC scanning routines are adapted from the code distributed with the catalog.