[ Basic Info | References | User Guide ]
Basic Information on imstat
Task: 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-keyword.
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 plotheader 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.
Key: in
This is the standard name for an input dataset -- usually
an image, though sometimes either an image or visibility dataset
or some foreign dataset format. Some tasks support multiple
input datasets at a time (with wildcard supported) whereas
others can handle only a single one at a time. There is
generally no default input name.
Key: region
the userguide.
This selects a subregion of an image. Multiple subregions can be
selected, which are "ored" together. The following subcommands are
recognized (each of which can be abbreviated to uniqueness).
images(z1,z2)
Select image planes z1 to z2 inclusive. z2 defaults to z1.
quarter(z1,z2)
Select the inner quarter of the image planes z1 to z2 inclusive.
If both z1 and z2 are missing, then all planes are selected. If
only z2 is omitted, z2 defaults to z1.
boxes(xmin,ymin,xmax,ymax)(z1,z2)
Select the pixels within a box with corners xmin,ymin,xmax,ymax.
z1 and z2 are the same as in the "image" subcommand. If z1 and z2
are omitted, all planes are selected.
polygon(x0,y0,x1,y1,x2,y2,...)(z1,z2)
Select the pixels within the polygon defined by the list of vertices.
z1 and z2 are the same as in the "image" subcommand. If z1 and z2 are
missing, all planes are selected. If only z2 is omitted, it defaults
to z1.
mask(file)
Select pixels according to the mask given in the file.
The units of the numbers given in the above commands are, in
general, absolute pixels. But this can be changed (and rechanged)
by using one of the following subcommands.
abspixel
Coordinates are interpreted as absolute pixel values, the default.
relpixel
Coordinates are relative to the reference pixel of the map.
relcenter
Coordinates are relative to the central pixel of the map,
(defined as (naxis1/2+1,naxis2/2+1)).
arcsec
Coordinates are in arcseconds, relative to the reference pixel.
kms
Coordinates in the third dimension are in km/s.
Key: plot
This selects which statistic will be plotted as function of e.g.
velocity. 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
Key: options
The options control the characteristics of the plot.
Possible options are (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 a two-sided. Useful for
Zeeman work.
'noheader' Do not write the header information, just the numbers,
producing an ASCII file for a plotting program
'nolist' Do not write the statistics to the screen/logfile
'eformat' Always use format 'e' instead of 'g' to write results
'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 autoscaling)
'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
Key: cutoff
All datavalues 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.
Key: beam
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.
Key: axes
This keyword gives the axis (for profiles) or axes (for planes) along
which statistics are calculated. E.g. 'axes=ra,dec' means that
statistics are found for ra-dec planes (irrespective of their
orientation in the dataset). 'axes=vel' gives statistics of a velocity
profile at each ra and dec position in the selected region.
The default is to calculate statistics for each ra,dec plane as
function of velocity.
Possible values for are: 'rascension', 'declination', 'longitude',
'latitude', 'glongitude', 'glatitude', 'velocity', 'frequency',
'channel', 'stokes', 'x', 'y', 'z', 'a', 'b'. Upper case and
capitalized versions and the string 'R.A.' are also recognized.
Minimal matching is applied. One or two axes may be given.
Key: device
This keyword is used to specify the plotting device. It uses
the normal PGPLOT format of
file/type
or
device/type
Usually there exists a default file name or device name.
The part after the slash gives the plotter type. Examples of the
type are:
xs X-windows output. This window is resizeable and
persistent. Prepending a number allows you to use multiple
windows, e.g. 1/xs, 2/xs etc.
xd X-windows output. A transient window that disappears
when your task exists.
ps Postscript (landscape mode).
vps Postscript (portrait mode).
cps Color postscript (landscape mode).
gif gif files. Only supported with g77, not gfortran.
vcps Color postscript (portrait mode).
tek Tektronix 4010 or equivalent.
xterm Xterm window (better for simple plots over slow X links).
A `?' as device name generates a complete list of the recognized
types (which will most likely vary from system to system).
Files created for hardcopy devices must be spooled to the printer
separately. The command needed for this is site and device specific.
Key: log
If specified, output is written to the file given by log= instead
of to the terminal.