Examples for imhead

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6.2.1 Examples for imhead

The following uses the example images from NGC5921 (§ F.1).

We can print the summary to the logger:

CASA <51>: imhead(’ngc5921.demo.cleanimg.image’,mode=’summary’)

prints in the logger:

##### Begin Task: imhead             #####
  Image name       : ngc5921.demo.cleanimg.image
  Object name      : N5921_2
  Image type       : PagedImage
  Image quantity   : Intensity
  Pixel mask(s)    : None
  Region(s)        : None
  Image units      : Jy/beam
  Restoring Beam   : 52.3782 arcsec, 45.7319 arcsec, -165.572 deg

  Direction reference : J2000
  Spectral  reference : LSRK
  Velocity  type      : RADIO
  Rest frequency      : 1.42041e+09 Hz
  Pointing center     :  15:22:00.000000  +05.04.00.000000
  Telescope           : VLA
  Observer            : TEST
  Date observation    : 1995/04/13/00:00:00
  Telescope position: [-1.60119e+06m, -5.04198e+06m, 3.55488e+06m] (ITRF)

  Axis Coord Type      Name             Proj Shape Tile   Coord value at pixel    Coord incr Units
  ------------------------------------------------------------------------------------------------
  0    0     Direction Right Ascension   SIN   256   64  15:22:00.000   128.00 -1.500000e+01 arcsec
  1    0     Direction Declination       SIN   256   64 +05.04.00.000   128.00  1.500000e+01 arcsec
  2    1     Stokes    Stokes                    1    1             I
  3    2     Spectral  Frequency                46    8   1.41279e+09     0.00 2.4414062e+04 Hz
                       Velocity                               1607.99     0.00 -5.152860e+00 km/s
##### End Task: imhead

If you choose mode=’list’, you get the summary in the logger and a listing of keywords and values to the terminal:

CASA <52>: imhead(’ngc5921.demo.cleanimg.image’,mode=’list’)
  Out[52]:
{’beammajor’: 52.378242492675781,
’beamminor’: 45.731891632080078,
’beampa’: -165.5721435546875,
’bunit’: ’Jy/beam’,
’cdelt1’: ’-7.27220521664e-05’,
’cdelt2’: ’7.27220521664e-05’,
’cdelt3’: ’1.0’,
’cdelt4’: ’24414.0625’,
’crpix1’: 128.0,
’crpix2’: 128.0,
’crpix3’: 0.0,
’crpix4’: 0.0,
’crval1’: ’4.02298392585’,
’crval2’: ’0.0884300154344’,
’crval3’: ’I’,
’crval4’: ’1412787144.08’,
’ctype1’: ’Right Ascension’,
’ctype2’: ’Declination’,
’ctype3’: ’Stokes’,
’ctype4’: ’Frequency’,
’cunit1’: ’rad’,
’cunit2’: ’rad’,
’cunit3’: ’’,
’cunit4’: ’Hz’,
’datamax’: ’ Not Known ’,
’datamin’: -0.010392956435680389,
’date-obs’: ’1995/04/13/00:00:00’,
’equinox’: ’J2000’,
’imtype’: ’Intensity’,
’masks’: ’ Not Known ’,
’maxpixpos’: array([134, 134,   0,  38], dtype=int32),
’maxpos’: ’15:21:53.976, +05.05.29.998, I, 1.41371e+09Hz’,
’minpixpos’: array([117,   0,   0,  21], dtype=int32),
’minpos’: ’15:22:11.035, +04.31.59.966, I, 1.4133e+09Hz’,
’object’: ’N5921_2’,
’observer’: ’TEST’,
’projection’: ’SIN’,
’reffreqtype’: ’LSRK’,
’restfreq’: [1420405752.0],
’telescope’: ’VLA’}

Note that this list is a return value and can be captured in a variable:

mylist = imhead(’ngc5921.demo.cleanimg.image’,mode=’list’)

The values for these keywords can be queried using mode=’get’. At this point you should capture the return value:

CASA <53>: mybmaj = imhead(’ngc5921.demo.cleanimg.image’,mode=’get’,hdkey=’beammajor’)

CASA <54>: mybmaj
Out[54]: {’unit’: ’arcsec’, ’value’: 52.378242492699997}

CASA <55>: myobserver = imhead(’ngc5921.demo.cleanimg.image’,mode=’get’,hdkey=’observer’)

CASA <56>: print myobserver
{’value’: ’TEST’, ’unit’: ’’}

You can set the values for these keywords using mode=’put’. For example:

CASA <57>: imhead(’ngc5921.demo.cleanimg.image’,mode=’put’,hdkey=’observer’,hdvalue=’CASA’)
Out[57]: ’CASA’

CASA <58>: imhead(’ngc5921.demo.cleanimg.image’,mode=’get’,hdkey=’observer’)
Out[58]: {’unit’: ’’, ’value’: ’CASA’}

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