Description

imval task: Get the data value(s) and/or mask value in an image.

Get the data value(s) and/or mask value in an image.

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 (e.g., 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 (i.e., 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 "AND"ing the image mask values with the specified region mask values, e.g., 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. In this case, box="" will result in the details of the direction plane (i.e., RA/Dec or Galactic latitude/longitude) reference pixel to be returned in the selected frequency and stokes planes, while box="-1" will result in details for all pixels in the selected frequency and stokes planes being returned.

Note that if only the pixel and/or mask values are required, ia.getchunk() and ia.getregion() also will provide these values.

For directed output, run as:

myoutput = imval()

The general procedure to obtain data values of an image and display them is:

#Specify inputs, then
myoutput = imval()
#or specify inputs directly in calling sequence to task
myoutput = imval(imagename='image.im', etc)
myoutput['KEYS'] #will contain the result associated with any of the keys given below
KEYS 
DESCRIPTION
blc absolute PIXEL coordinates of the bottom left corner of the bounding box surrounding the selected region
trc the absolute PIXEL coordinates 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.
coords The numerical values of the coordinates associated with each data value. Each set of coordinate values is ordered according to the coordinate axis ordering.

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 information on how to manipulate them see: http:numpy.scipy.org/#array_interface