File-format-agnostic loading of astronomical images (`pwkit.astimage`)¶

pwkit.astimage – generic loading of (radio) astronomical images

Use open (path, mode) to open an astronomical image, regardless of its file format.

The emphasis of this module is on getting 90%-good-enough semantics and a really, genuinely, uniform interface. This can be tough to achieve.

class pwkit.astimage.AstroImage(path, mode)[source]¶

An astronomical image.

path: The filesystem path of the image.
mode: Its access mode: ‘r’ for read, ‘rw’ for read/write.
shape: The data shape, like numpy.ndarray.shape.
bmaj: If not None, the restoring beam FWHM major axis in radians.
bmin: If not None, the restoring beam FWHM minor axis in radians.
bpa: If not None, the restoring beam position angle (east from celestial north) in radians.
units: Lower-case string describing image units (e.g., jy/beam, jy/pixel). Not standardized between formats.
pclat: Latitude (usually dec) of the pointing center in radians.
pclon: Longitude (usually RA) of the pointing center in radians.
charfreq: Characteristic observing frequency of the image in GHz.
mjd: Mean MJD of the observations.
axdescs: If not None, list of strings describing the axis types. Not standardized.
size: The number of pixels in the image (=shape.prod ()).

Methods:

close: Close the image.
read: Read all of the data.
write: Rewrite all of the data.
toworld: Convert pixel coordinates to world coordinates.
topixel: Convert world coordinates to pixel coordinates.
simple: Convert to a 2D lat/lon image.
subimage: Extract a sub-cube of the image.
save_copy: Save a copy of the image.
save_as_fits: Save a copy of the image in FITS format.
delete: Delete the on-disk image.

axdescs = None¶: If not None, list of strings describing the axis types; no standard format.

bmaj = None¶: If not None, the restoring beam FWHM major axis in radians

bmin = None¶: If not None, the restoring beam FWHM minor axis in radians

bpa = None¶: If not None, the restoring beam position angle (east from celestial north) in radians

charfreq = None¶: Characteristic observing frequency of the image in GHz

mjd = None¶: Mean MJD of the observations

pclat = None¶: Latitude of the pointing center in radians

pclon = None¶: Longitude of the pointing center in radians

shape = None¶: An integer ndarray of the image shape

subimage(pixofs, shape)[source]¶

Extract a sub-cube of this image.

Both pixofs and shape should be integer arrays with as many elements as this image has axes. Thinking of this operation as taking a Python slice of an N-dimensional cube, the i’th axis of the sub-image is slices from pixofs[i] to pixofs[i] + shape[i].

units = None¶: Lower-case string describing image units (e.g., jy/beam, jy/pixel)

class pwkit.astimage.FITSImage(path, mode)[source]¶: A FITS format image.

class pwkit.astimage.MIRIADImage(path, mode)[source]¶: A MIRIAD format image. Requires the mirtask module from miriad-python.

class pwkit.astimage.PyrapImage(path, mode)[source]¶: A CASA-format image loaded with the ‘pyrap’ Python module.

class pwkit.astimage.SimpleImage(parent)[source]¶: A 2D, latitude/longitude image, referenced to a parent image.

exception pwkit.astimage.UnsupportedError(fmt, *args)[source]¶

File-format-agnostic loading of astronomical images (pwkit.astimage)¶

File-format-agnostic loading of astronomical images (`pwkit.astimage`)¶