expkey parameter for imstack

[simonrw]

The imstack program includes headers which have not been considered:

--lthr=5
    The lower threshold for clipping in units of background sigma.

--hthr=5
    The upper threshold for clipping in units of background sigma

--method=1
    The interpolation method to be used -- the following integer values are allowed:
    0: (nearest neighbour) An input pixel is mapped to the location on the output grid that is nearest to its equatorial position
    1: (bi-linear interpolation) An input pixel is divided up into the four pixels on the output grid that surround the input equatorial position. The   fraction going into each output pixel depends on the amount of overlap of the input pixel.

--nplate=6
    If a catalogue list is specified in cats then this is the number of plate constants to fit to the pixels space coordinates of the matched objects.

--expkey=EXPTIME
    Name of the keyword which stores the exposure time. 

--(no)seewt (no)
    Weight the images by the inverse of the square root of the average seeing.

An exploration of these settings would be good, most notably the expkey option as its default is not the same as ours (exposure).

[simonrw]

It seems the expkey does nothing. Either it never did anything or it's clever enough to consider the correct header keyword.