imhead – List, get and put image header parameters – analysis, information, manipulation task

Description

List, get and put image header parameters.

This task allows the user to manipulate metadata associated with a CASA image. Both float and complex valued images are fully supported.

For measurement sets, the task vishead should be used.

Parameters

Title

Parameter	Default	Description
imagename	''	Name of the input spectral line image
mode	'summary'
hdkey	''	The associated keyword for modes “add”, “del”, “get”, or “put”. Only “get” will work if the image is read-only (eg, a FITS image).
hdvalue	''	Value of keyword for modes add or put.
verbose	False	Give a full listing of beams or just a short summary? Only used when the image has multiple beams and mode=”summary”.

Parameter Explanations

imagename

''

Input image cube.

Default: none

Example: imagename=’ngc5921_task.image’

mode

'summary'

Mode of operation.

Default: summary Options: “add”, “del”, “get”, “history”, “list”, “put”, or “summary”.

• add: Add a new metadata value to the image. The behavior of mode=”add” depends on the keyword. In general, the return value will be True if the operation succeeds, or False if it fails or is not supported. If unsuccessful or not supported, a message is normally logged which describes the failure. In most cases, you probably want to use mode=’put’ rather than mode=’add’. We continue to support mode=’add’ mainly for backward compatibility.

• del: Delete a key or reset its value to a fidicual value if possible. Ignores all but imagename, mode, and hdkey parameters. In general, the return value will be True if the operation succeeds, or False if it fails or is not supported. If unsuccessful or not supported, a warning message is normally logged which describes the failure.

• get: Return the specified keyword value. Ignores all but imagename, mode, and hdkey parameters.

• history: Log image history. Ignores all but imagename and mode parameters.

• list: Show supported keywords and their values. Ignores all but imagename and mode parameters. put: Modify the specified value associated with the keyword. True is returned if the metadatum was successfully modified, False otherwise. Normally, a diagnostic message is logged if there is a failure. Only the parameter specified is modified; eg, no modification of reference direction occurs to implicitly account for precession to a new reference frame.

• summary: Log a summary of the image and return a dictionary of various metadata values. Ignores all but imagename and mode parameters.

IMPORTANT: Lists of keywords for the various modes of operation are given in the imhead task pages of CASA Docs (https://casa.nrao.edu/casadocs/).

The behavior of mode=’add|del|get depends on the keyword. Modes “add”, “del”, and “put” will not work if the image is read-only (eg a FITS image).

NOTE: Only limited checking is implemented to ensure modifying a specific value will leave the image metadata in a consistent state, so, if one is not careful, one could end up with an image that has an inconsistent set of metadata and is therefore, nonsensical and useless That is, PROCEED AT YOUR OWN RISK when using modes add, del, or put.

hdkey

''

Keyword to use with get, put, add, or del.

Subparameter of mode=get|put|add|del

Only “get” will work if the image is read-only (eg, a FITS image).

Example: hdkey=’telescope’

hdvalue

''

Keyword value used for modes ‘put’ and ‘add’.

Subparameter of mode=’put|add’ (‘del’)

Also used for mode=”del” when hdvalue=”masks.

Example: hdvalue=’VLA’

verbose

False

Give a full listing of beams or just a short summary? Only used when the image has multiple beams and mode=”summary”.