The Grammar of EasyFITS

FITS file may have quite complex structure and EasyFITS implement a grammar that is intended to make clear the intention when reading the code and to help to guess the correct syntax when writing code. Most of the assumed rules should be familiar to Julia users.

The general syntax to read some data in a FITS file follows the following pattern:

data = read([type,] src[, what...])

where:

• type is an optional Julia type to specify the expected type of the result.

• src is the source to read: a filename name, a FitsFile object representing an open FITS file, or a FitsHDU object representing a FITS Header Data Unit in an open FITS file.

• what... denotes optional arguments to specify which part(s) to read: index ranges of an array if reading a FITS image extension, column(s) and rows if reading a FITS table extension.

Overwriting the contents of an existing destination object dest may be done by:

read!(dest, src, what...)

or by:

merge!(dest, src, what...)

when the intention is to preserve (part of) the contents of dest, or also by:

push!(dest, src, what...)

to append the read data to the contents of dest.

Create a new HDU in file:

hdu = write(file, hdutype, defs...)

Write some data in a FITS file:

write(file, header, data) -> file

which yields file so that chaining calls is possible to write several HDUs in a row:

write(write(write(file, header1, data1), header2, data2), header3, data3)

which is equivalent to the more readable form:

write(file, header1, data1, header2, data2, header3, data3)