List, get and put image header parameters
This task allows the user to manipulate some meta-data parameters in an
image. The mode='list' shows those keywords that are
presently implemented, with their values. The contents associated
with the keywords can be obtained (get) and changed (put).
Additional image parameter listings are available.
[For visibility files, the taskname='vishead' should be used.]
The modes that are available are:
list --- Lists the image header keywords and values.
Use this if 'get' and 'put' are executed.
get --- Get the specified keyword value(s) from the image
put --- Put the specified keyword value(s) into the image
history --- Display the history information in hte CASA logger.
summary --- Information summarizing the CASA image file.
fits --- Lists the header information in a FITS style (not available)
add --- Adds a new header key. Use with caution
del --- Delete a header key, hdkey. Use with caution
Parameters currently implemented are listed using mode = 'list'
beammaj Major axis of the clean beam
beammin Minor axis of the clean beam
beampa Position angle of the clean beam
NOTE: If the image contains multiple beams, use mode="summary" to get
a listing.
bunit Brightness unit (K, Jy/beam, etc)
cdeltn Pixel size, nth axis (max n is 4)
crpixn Pixel coordinate of reference point, nth axis
crvaln Pixel location of reference point, nth axis
ctypen Axis name, nth axis
cunitn Pixel units, nth axis
datamax Maximum pixel value in image
datamin Minimum pixel value in image
date-obs Date of the observation
equinox Reference frame for directional coordinates
imtype Image type: intensity,
minpos
minpixpos
maxpos
maxpixpos
object Source name
observer Observer name
projection Image projection ('SIN','TAN', or 'ZEA')
reffreqtype Reference frame for the spectral coordinates
restfreq Rest Frequency
shape Number of pixels along each axis
telescope Telescope name
Keyword arguments:
imagename --- Name of input image
default: none; example: imagename='ngc5921_task.image'
mode --- Mode: options:
default: none; 'list', 'summary', 'fits', 'history',
'get', 'put', 'add', and 'del'
NOTE: 'add' and 'del' should be used with caution
hdkey --- keyword to use with get, put, add, or del
default: none; example: hdkey='telescope'
hdvalue --- keyword value that is 'got', or to be 'put' or
to be 'added'
default: ''; example: hdvalue='VLA'
hdcomment --- comment to be stored with the keyword for mode='put' or mode='add'
Examples:
hdkey='date-obs';hdvalue='2007/06/20/00:00:00'
hdkey='beammajor';hdvalue='55arcsec'
hdkey='beampa'';hdvalue='0deg'
hdkey='restfrequency';hdvalue='1.421GHz'
hdkey='restfrequency';hdvalue='1.421GHz, 115.272GHz'
hdkey='projection';hdvalue='TAN'
hdkey='cdelt4';hdvalue=24415.05
hdkey='cdelt1';hdvalue='7.75e-5deg'
hdkey='crval1';hdvalue=qa.quantity( '763180', 'arsec')
hdkey='crval1';hdvalue='14:07:58'
hdkey='crval4';hdvalue='6250000Hz'
hdtype --- Used only with 'add' mode. It is the data type that
is used to store the hdkey. It can not be used to
change the data type of an exiting keyword.
options: bool, int, string, doubple, complex
default: none; example hdtype='double'
Note that hdvalue will contain numbers, strings as well as units.
If mode="summary", verbose=True and the image contains multiple beams, the output,
will contain information on every beam in the dataset. If mode="summary",
verbose=False and the image has multiple beams, only a brief summary of
beams for each polarization is listed. In this
case, the beams with the maximum area, the minimum area, and the median area for
each polarization are listed. If mode is not "summary" and/or the image does not
have multiple beams, verbose is not used.
Examples:
1) get the clean beam from one image and put it in a second image
Get the clean beam from image1 into hdvalue
imagename = 'image1.im'; mode = 'get'; hdkey = 'beam'
hdvalue = imhead()
print hdvalue # to see values
To then put the clean beam into image2
imagename = 'image2.im', mode = 'put'; imhead()
2) Most output values are dictionaries:
mode = 'get'; hdkey = 'maxpos'; aa = imhead()
would give for the command print aa
{'value': '03:19:48.160, +41.30.42.103, I, 4.88163e+09Hz', 'unit': ''}
print aa['value'] gives
03:19:48.160, +41.30.42.103, I, 4.88163e+09Hz
print aa['value'[1][0:12] gives 03:19:48.160
mode = 'get'; hdkey = 'crpix1'; aa = imhead()
would give for the command print aa
{'value': '128.0', 'unit': ''}
print aa['value'] gives
128.0 (a string)
3) The use of put is a bit more straight-forward
mode = 'put'; hdkey = 'crpix1'; hdvalue = '200'; imhead()
then
mode = 'get'; hdkey = 'crpix1'; aa = imhead() would give
{'value': '200.0', 'unit': ''}
1.8.0