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NRAO Home > CASA > CASA Task Reference Manual |
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0.1.63 imval
Requires:
Synopsis
Get the data value(s) and/or mask value in an image.
Arguments
Outputs |
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blc |
| Bottom-left corner of the bounding box that encloses the
region being examined..
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| allowed: | any |
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| Default: | variant | |
trc |
| top-right corner of the bounding box that encloses the
region being examined.
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| allowed: | any |
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| Default: | variant | |
axes |
| A listing of the axis index numbers and the data stored
along that axis.
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| allowed: | any |
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| Default: | variant | |
unit |
| The units the data values are stored and displayed in.
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| allowed: | any |
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| Default: | variant |
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data |
| The pixel values found at the given point(s).
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| allowed: | any |
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| Default: | variant |
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mask |
| The mask values found at the given point(s).
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| allowed: | any |
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| Default: | variant |
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Inputs |
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imagename |
| Name of the input image
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| allowed: | string |
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| Default: |
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region |
| Region selection. Default is to use the full image.
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| allowed: | any |
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| Default: | variant
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box |
| Rectangular region(s) to select in direction plane.
Default is to use the entire direction plane.
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| allowed: | string |
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| Default: |
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chans |
| Channels to use. Default is to use all channels.
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| allowed: | string |
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| Default: |
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stokes |
| Stokes planes to use. Planes specified must be
contiguous. Default is to use all Stokes planes.
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| allowed: | string |
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| Default: |
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void
Example
The data point(s) to be retrieved are those found in the specified
region, which may be:
1. A region file or text string, with the following caveat:
* If the specified region is complex (eg, a union or intersection of multiple regions,
only the first simple region in this set is used.
* If the region is not rectangular, then the rectangular region that circumscribes the
specified region (ie the bounding box) is used to retrieve values, since the returned
arrays must be rectangular. The resulting mask values in this case are the result of
anding the image mask values with the specified region mask values, eg
if a pixel falls outside the specified region but within the bounding box, its returned
mask value will be false even if its image mask value is true.
2. A region specified by a set of rectangular
pixel coordinates, the channel ranges and/or the Stokes.
For directed output, run as
myoutput = imval()
Keyword arguments:
imagename -- Name of input image
Default: none; Example: imagename=’ngc5921_task.im’
region -- Region selection. Default is to use the full image.
Example: region=’myimage.im.rgn’
region=’region1’
box -- Rectangular region to select in direction plane. Default is to use the entire direction plane.
Default: ’’ (referencepixel values for the Directional coord);
Example: box=’10,10,50,50’
box = ’10,10,30,30,35,35,50,50’ (two boxes)
chans -- Channels to use. Default is to use all channels.
stokes -- Stokes planes to use. Planes specified must be contiguous. Default is to use all Stokes planes.
Example: stokes=’IQUV’;
stokes=’I,Q’
General procedure:
1. Specify inputs, then
2. myoutput = imval()
or specify inputs directly in calling sequence to task
myoutput = imsval(imagename=’image.im’, etc)
3. myoutput[’KEYS’] will contain the result associated with any
of the keys given below
KEYS CURRENTLY AVAILABLE
blc - absolute PIXEL coordinate of the bottom left corner of
the bounding box surrounding the selected region
trc - the absolute PIXEL coordinate of the top right corner
of the bounding box surrOunding the selected region
axes - List the data stored in each axis of the data block.
unit - unit of the returned data values.
data - data value(s) found in the given region
mask - mask value(s) found in the given region. See important
note above regarding returned mask values for
non-rectangular regions.
NOTE: The data returned is in the same order as it is internally
stored, typically RA, DEC, spectral, stokes. Also both the data
and mask values are returned as Python Numpy arrays, for more
information on how to manipulate them see
http://numpy.scipy.org/#array_interface
Additional Examples
# The value and mask value at a single point (5,17,2,Q)
imval( ’myImage’, box=’5,5,17,17’, chans=2, stokes=’Q’ )
# Select and report on two box regions
# box 1, bottom-left coord is 2,3 and top-right coord is 14,15
# box 2, bottom-left coord is 30,31 and top-right coord is 42,43
# Note that only the boxes for the
imval( ’myImage’, box=’2,3,14,15;30,31,42,43’ )
# Select the same two box regions but only channels 4 and 5
imval( ’myImage’, box=’2,3,14,15;30,31,42,43’, chan=’4~5’ )
# Select all channels greater the 20 as well as channel 0.
# Then the mean and standard deviation are printed
# Note that the data returned is a Python numpy array which
# has built in operations such as min, max, and means as
# demonstrated here.
results = imval( ’myImage’, chans=’>20;0’ )
imval_data=results[’data’]
mask=results[’mask’]
# holds the absolute coordinates of the associated pixels in imval_data
coords = results[’coords’]
print "Data max: ", imval_data.max(), " mean is ", imval_data.mean()
swapped_data=imval_data.swapaxes(0,2)
swapped_mask=mask.swapaxes(0,2)
print "Data values for 21st channel: \n", swapped_data[0]
print "Mask values for 21st channel: \n", swapped_mask[0]
More information about CASA may be found at the
CASA web page
Copyright © 2016 Associated Universities Inc., Washington, D.C.
This code is available under the terms of the GNU General Public Lincense
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