SEt
Allows you to set various internal LEXTRCT default parameter values.
Parameters are currently arranged in groups. These groups are Ccd
for parameters useful when reading X-ray CCD data, Display for
parameters that affect the default appearance of the displayed image,
Instrument for instrument specific parameters, Map for parameters related
to the size of the internal data array or map, Scale define some
image scaling parameters and Time where you can override the integration
time.
To see a list of all parameters and the current values use the "Show"
command. If you just want to inspect the Display parameters you can
use "SHow Display" and finally if you want to inspect a single
parameter, you can use "SHow Display Scale".
If you want a list of the options, enter the command without the
actual parameter value and lextrct will display the legal options.
Thus "SEt DIsplay Scale" would list all the possible Display Scale
values.
Ccd
X-ray CCD data comes in groups of 3x3 pixels. The DN in the center
pixel is allows included in the PHA, however, DN from the other
pixels is only added in if it exceeds the Split Level. The Slevel
parameter can be used to set this value. Thus
LEXTRCT> Set Ccd Slevel 10
would reset the Slevel parameter to 10. This means the next time
spectral data is read from the FITS file, data from the adjacent
pixels will only be added if the DN in that pixels exceeds 10.
The "standard" value for slevel is 13 for ACIS. We think 27 is
better for ASCA but you should check.
Disp
The Display group contains parameters that affect the default appearance
of the image after issuing the Plot command. These options are
CBar [ON/OFF] controls whether the Color Bar is displayed or not.
CCT table allows you to change the default color table. See the
CCT subtopic for details on Color tables.
CI # This controls the color index that is used when overplotting
(IProj, DB, OGrid).
LW # This controls the Line Width used when overplotte (IProj, DB,
OGrid, OSource).
Scale name, where name is one of HIstogram, LInear, LOg, SQRT. Where
Linear indicates linear image scaling, Log indicates Log, SQRT
indicates square root scaling, and HIstogram attempts to do
an histogram equalization.
CCT
Change the color look-up table. You can either select a builtin
color table or read a color table from a disk file. All builtin color
tables are described with an integer number. Use 'SEt Dis CCt ?'
to get a list of builtin color tables. Thus 'cct 1' will select the
first builtin color table.
If the argument is not an integer but a string, then CCT assumes you
want to read a color table from a disk file. Thus 'SEt Disp cct next'
would try to open the 'next.ct' file in the current directory and
load it.
The current convention for color tables is to start with darker colors
and then get lighter. You can easily invert a color table by preceeding
the argument with a minus '-' sign. Thus 'cct -1' would load first
builtin color table inverted. Likewise, 'cct -next' would invert the
color table from the file 'next.ct'
file_format
Color table files are simple ASCII files with 4 numbers per line.
The first number in each line is the normalized color index. This
number must lie in the range 0.0 to 1.0 inclusive. The software will
automatically map the normalized color index in to color index range
used by PGPLOT to display images. The advantage of using normalized
color index is that the color table becomes device independent, and
so images will appear approximately the same color on a wide variety
of devices.
The remaining three numbers on a line of a color table file are the
red, green, and blue intensities. Again these numbers should also
range between 0.0 and 1.0 inclusively.
Fits
By default LEXTRCT tries to read event data from the FITS extension
with EXTNAME='EVENTS'. If you are reading a FITS file with events
like data in an extension with a different name, then you will need
to tell LEXTRCT where the event data is hidden. The best way to find
out is to use the LEXTRCT command THead to type out the FITS headers
and look for the FITS keyword EXTNAME. For example, assume that
event-like data is in EXTNAME='M1AUX1', then you tell LEXTRCT:
Set Fits Extension m1aux1
Map
Lextrct reads the data into an internal array called the Map array.
In certain cases you do not want to use the entire array (you have
a slow computer or only want a bit of the image. The Size parameter
allows you to define a smaller map size. Thus
SEt Map Size 100 1000
Would define a 100x1000 array where the first coordinate is the
X dimension and the second the Y.
Psf
Controls parameters that are used to calculate the PSF.
Cent
Defines the location where the PSF is smallest. This defaults to
where the optical axis intersects the detector.
File
Allows the PSF to be read from an external file (currently contains
parameters hardwired for ACIS S).
Model
set psf model $
where $ is Cgau, Egau, CHandra, or Moff. The default is CGa where
the PSF is modeled as a circular gaussian. Sigma is computed from
the values set via set psf sig and set psf quad.
For psf model CHandra the PSF is modeled as an ellipical gaussian.
The rotation angle roughly (within a few degees) matches the angle
seen in the Chandra PSF. Also sigx and sigy are interpolated from
fits done to the PSFLIB PSF images.
psf Model Egau is similar to the Chandra model except the parameter
values are now totally set by the user. PSF sig sets sigx, and
the eccentricity and rotation are set via 'set psf pars'.
Egau and CHandra also affect the MBad File command and the source
fitting FF commands. For MBad File, the source region marked is now
an ellipse. For FF the fit function is now an ellipical gaussian
with starting parameters from the source finding default.
psf model Moffat models the PSF with a Moffat function. Moffat includes
an index which is set via ths 'SET PSF Parms' command
Roll
The image (i.e., spacecraft) roll angle. This is only needed when
reading the PSF from an external file, since the file is typically
in detector coordindates and the image is in sky.
Sig
The gaussian sigma in detector pixels at the Center location.
psf_sig = Sig + Quad*R**2
Pars
For the Egau and Moffat functions require additional parameters.
If either of these models is used, then this function can be used
to set the additional parameters.
For Egaus the first number (parameter value) is the eccentricity of
the ellipse and must lie in the range [0.0,1.0). The second number
is the rotation angle and must lie in the range [-90, +90].
For Moffat, the first number is the index and must lie in the range
[0.0, 20.0].
Quad
If Quad is non-zero then the gaussian sigma is
psf_sig = Sig + Quad*R**2
Where R is distance from Center in pixels.
Time
Lextrct attempts to read the integration time from the FITS file.
However, it often fails because some creative made up FITS keyword
was used, or more likely the FITS writer forgot to include this number.
Since lextrct uses the integration time to create a background
subtracted image, the "SEt Time" command can be used to set the
LEXTRCT> SEt Time Data 1000 ! Assume data was integrated for 1000 secs.
LEXTRCT> SEt Time Back 100 ! Assume data was integrated for 100 secs.
WCS
By default lextrct reads the World Coordinate System (WCS) parameters
from the FITS file. If some or all of the WCS parameters are missing
or if you want to change the mapping to World coordinates, then
you can set the WCS parameters by hand.
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