Regridding an Image (imregrid)

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6.11 Regridding an Image (imregrid)

Inside the Toolkit:

More complex coordinate system and image regridding operation can be carried out in the toolkit. The coordsys (cs) tool and the ia.regrid method are the relevant components.

It is occasionally necessary to regrid an image onto a new coordinate system. The imregrid task will regrid one image onto the coordinate system of another, creating an output image. In this task, the user need only specify the names of the input, template, and output images.

If the user needs to do more complex operations, such as regridding an image onto an arbitrary (but known) coordinate system, changing from Equatorial to Galactic coordinates, or precessing Equinoxes, the CASA toolkit can be used (see sidebox). Some of these facilities will eventually be provided in task form.

The default inputs are:

#  imregrid :: regrid an image onto a template image
imagename           =         ’’        #  Name of input image
template            =         ’’        #  Name of reference image
output              =         ’’        #  Name of output regridded image
async               =      False        #

The output image will have the data in imagename regridded onto the coordinate system provided by the template parameter. template is used universally for a range of ways to define the grid of the output image:

a template image: specify an image name here and the input will be regridded to the same 3-dimensional coordinate system as the one in template. Values are filled in as blanks if they do not exist in the input. Note that the input and template images must have the same coordinate structure to begin with (like 3 axes)
a coordinate system (reference code): to convert from one coordinate frame to another one, e.g. from B1950 to J2000, the template parameter can be used to specify the output coordinate system. These following recognized keywords are supported: ’J2000’, ’B1950’, ’B1950_VLA’, ’GALACTIC’, ’HADEC’, ’AZEL’, ’AZELSW’, ’AZELNE’, ’ECLIPTIC’, ’MECLIPTIC’, ’TECLIPTIC’, ’SUPERGAL’
’get’: This option returns a python dictionary in the {’csys’: csys_record, ’shap’: shape} format
a python dictionary: In turn, such a dictionary can be used as a template to define the final grid

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