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Basic Information on imstat
Purpose: calculate and plot map statistics
Categories: map analysis
IMSTAT calculates statistics for images. These are the sum,
mean, rms, maximum and minimum value of a region. Statistics
can be found for profiles or planes, specified using the axes
The data can be converted to Kelvin, by using 'options=tb' and
the beam keyword.
Output can be written to the terminal, a log file, or a plot.
The options keyword gives control over the plot.
The plot header can be suppressed by using options=noheader.
An alternative title can be put on the plot by options=title.
A useful combination is 'options=noh,ti,title', to get only the
string 'title', instead of the full header.
Standard keyword in. See the help on in for more information.
Standard keyword region. See the help on region for more information.
One axis (for profiles) or two axes (for planes) for which
statistics are to be calculated. E.g. 'axes=spectral' computes
statistics of each spectrum in the selected region - whether
expressed as frequency, velocity, etc.
'axes=longitude,latitude' would compute statistics for each
celestial image plane in the dataset (regardless of
axes is case insensitive, and may be specified explicitly by
coordinate type (ctype), as listed by PRTHD. In this it is not
necessary to specify the algorithm code, e.g. 'RA' matches both
'RA---NCP' and 'RA---SIN', while 'VOPT' matches 'VOPT-F2W'.
Axes may also be specified via their order in the image as
'x', 'y', 'z', 'a', 'b', 'c', and 'd' for axes 1 to 7.
The following generic values are also understood: 'longitude'
('lng' or 'long'), 'latitude' (or 'lat'), and 'spectral' ('spc'
The default is 'x,y' if the input is multi-dimensional,
Selects the statistic to be plotted. Minimal matching is
applied. The default is 'rms'.
'sum' Plot the sum
'mean' Plot the mean
'rms' Plot the rms
'maximum' Plot the maximum
'minimum' Plot the minimum
Data values below the cutoff are not used for the calculation
of statistics. Give one real value. This may be followed by
the string ',abs' to get a cutoff in the absolute value of the
datavalues, or ',lower' to exclude all values above the cutoff.
Default is no cutoff.
Standard keyword device. See the help on device for more information.
Options controlling the characteristics of the plot (minimal
matching is done):
'tb' Convert the units to brightness temperature,
using the input for the beam keyword
'hanning,#' Hanning smooth the data first over # pixels (must
be an odd number)
'boxcar,#' Boxcar smooth the data first over # pixels
'deriv,#' Take the derivative after smoothing. If #=1 a
one-sided derivative is taken, for #=2 its
two-sided. Useful for Zeeman work.
'noheader' Do not write the header information, just the
numbers, producing an ASCII file for a plotting
'nolist' Do not write the statistics to the screen/logfile
'eformat' Always use format 'e' instead of 'g' to write
'guaranteespaces' Make sure there is always a space between
columns (at the cost of precision)
'xmin,#' Give lower x-value on axis
'xmax,#' Give upper x-value on axis
'ymin,#' Give lower y-value on axis
'ymax,#' Give upper y-value on axis
(for these four options the default is
'title,#1,#2,#3' Put the string #1 at x-position #2 and
y-position #3, with positions measured in units
of the coordinates on the axes. If 'title' is
the last option, the title is put in the upper
left hand corner.
'style,#' This selects the plot style.
#=connect means connect the datapoints
#=step means make one-bin wide connected
horizontal line segments
#=histo means bins are drawn as a horizontal line
surrounded by two vertical lines
If options=tb is used, imstat calculates the sum divided by the
sum of the beam to get the flux in the selected area, if the
units of the input data are 'per beam'. This is then converted
to Kelvin by dividing by 2k/lambda^2 * omega, where omega is
found from the beam keyword.
If the name of a dataset is given for 'beam', imstat assumes it
contains a beampattern and sums the data in a region of the same
size as the input region. Else, it assumes that 'beam' gives
the major and minor axes of the beam in arcsec and it calculates
the sum for a Gaussian beam of that size.
If 'beam' is omitted, but 'options=tb' was selected, the beam is
found from the header (items bmaj and bmin). If neither is
present, no conversion is done.
If specified, output is written to the file given by log=
instead of to the terminal.
Revision: 1.8, 2012/03/13 02:21:33 UTC
Generated by email@example.com on 13 Mar 2012