imcollapse – Collapse image along one axis, aggregating pixel values along that axis. – analysis task

Description

This task collapses an image along a specified axis or set of axes of N pixels to a single pixel on each specified axis. Both float valued and complex valued images are supported. It computes the specified aggregate function for pixel values along the specified axes and places those values in the single remaining plane of those axes in the output image.

The reference pixel of the collapsed axis is set to 0 and its reference value is set to the mean of the the first and last values of that axis in the specified region of the input image. Convolution to a common beam is not performed automatically as part of the preprocessing before the collapse operation occurs. Therefore, if the input image has per-plane beams, then the user should consider first smoothing the data to have the same resolution, and use the resulting image as the input for imcollapse.

Parameters

Title
Parameter	Default	Description
imagename	`''`	Name of the input image
function	`''`	Aggregate function to apply. This can be set one of flux, madm, max, mean, median, min, npts, rms, stddev, sum, variance, xmadm. Must be specified.
axes	`[ ]`	Zero-based axis number(s) or minimal match strings to collapse.
outfile	`''`	Name of output CASA image. Must be specified.
box	`''`	Rectangular region to select in direction plane. Default is to use the entire direction plane.
region	`''`	Region selection. Default is to use the full image.
chans	`''`	Channels to use. Default is to use all channels.
stokes	`''`	Stokes planes to use. Default is to use all Stokes planes.
mask	`''`	Mask to use. Default is none.
overwrite	`False`	Overwrite output image if it exists?
stretch	`False`	Stretch the mask if necessary and possible?

Parameter Explanations

imagename

''

Name of the input image: Default: none

Example: imagename=’ngc5921.im’

function

''

Function used to compute aggregation of pixel values along the collapsed axis.

Default: none Options: flux, madm, max, mean, median, min, npts, rms, stddev, sum, variance, xmadm

Minimum match is supported for the function parameter (eg, function=”r” will compute the rms of the pixel values).

If one specifies function=’flux’, the following constraints must be true: 1. The image must have a direction coordinate, 2. The image must have at least one beam, 3. The specified axes must be exactly the direction coordinate axes, 4. Only one of the non-directional axes may be non-degenerate, 5. The iamge brightness unit must be conformant with x*yJy/beam, where x is an optional unit (such as km/s for moments images) and y is an optional SI prefix.

axes

[ ]

Zero-based axis number(s) or minimal match strings to collapse.

Default: [0] Axes can be specified as a single integer or array of integers indicating the zero-based axes along which to collapse the image. Axes may also be specified as a single or array of strings which minimally and uniquely match (ignoring case) world axes names in the image (eg “dec” or [“ri, “d”] for collapsing along the declination axis or along the right ascension and declination axes, respectively).

outfile

''

Name of output CASA image. Must be specified.: Default: none

Example: outfile=’collapsed.im’

box

''

Rectangular region to select in direction plane.: Default: ‘’ (use the entire direction plane)

Example: box=”100,100,200,200”

region

''

Region selection.: Default: ‘’ (use the full image)

chans

''

Channels to use.: Default: ‘’ (use all channels)

stokes

''

Stokes planes to use.: Default: ‘’ (use all stokes planes)

mask

''

Mask to use.: Default: none

overwrite

False

Overwrite output image if it exists?: Default: False Options: False|True

stretch

False

Stretch the mask if necessary and possible?

Default: False Options: False|True

Stretch the input mask if necessary and possible. Only used if a mask is specified.