axis_increments_from_cd¶
- mpdaf.obj.axis_increments_from_cd(cd)[source]¶
Return the angular increments of pixels along the Y and X axes of an image array whose coordinates are described by a specified FITS CD matrix.
In MPDAF, images are a regular grid of square pixels on a flat projection of the celestial sphere. This function returns the angular width and height of these pixels on the sky, with signs that indicate whether the angle increases or decreases as one steps along the corresponding array axis. To keep plots consistent, regardless of the rotation angle of the image on the sky, the returned height is always positive, but the returned width is negative if a plot of the image with pixel 0,0 at the bottom left would place east anticlockwise of north, and positive otherwise.
- Parameters:
- cd
numpy.ndarray
The 2x2 coordinate conversion matrix, with its elements ordered for multiplying a column vector in FITS (x,y) axis order.
- unit
astropy.units.Unit
The angular units of the returned values.
- cd
- Returns:
- out
numpy.ndarray
(dy,dx). These are the angular increments of pixels along the Y and X axes of the image, returned with the same units as the contents of the CD matrix.
- out