def get_header2d(header3d):
    """Remove the spectral axis from a 3D FITS Header

        Args:
            header3d (astropy.io.fits.Header): Input 3D header.

        Returns:
            astropy.io.fits.Header: 2D Header object (spatial axes only)

        Example:

            If you wanted to collapse a cube to a 2D image and save it:

            >>> from astropy.io import fits
            >>> from cwitools import cubes
            >>> import numpy as np
            >>> mydata,header = fits.getdata("mydata.fits",header=True)
            >>> image_data = np.sum(mydata,axis=(0)) #Sum over wavelength
            >>> image_header = cubes.get_header2d(header)
            >>> image_fits = cubes.make_fits(image_data,image_header)
            >>> image_fits.writeto("image2D.fits")

            Note again - this example doesn't convert to surface-brightness or
            do any proper handling of units. That's up to you!

    """
    hdr2D = header3d.copy()
    for key in hdr2D.keys():
        if '3' in key:
            del hdr2D[key]
    hdr2D['NAXIS'] = 2
    hdr2D['WCSDIM'] = 2
    return hdr2D
