Conversion between FITSHeader and String

[aquatiko]

How can we convert a FITSHeader in a String format and vice-versa?
It would be great to modify a Header by making a WCSTransform object, making the changes and then saving that to original FITS file.
Using to_header from WCS.jl, we can get the header in string format but how can I write that to a FITSHeader?

[giordano]

Rather than converting a FITSHeader to a String, I think it could be useful a function that constructs a WCSTransform from the relevant keys of a FITSHeader. This function would live in WCS.jl, which however doesn't currently depend on FITSIO.jl

[aquatiko]

Do you mean, supplying specific fields present in WCS Header to a function along with a FITSHeader object?
I think that would be a easier workaround as we can use setproperty!() of WCS.jl and pass a symbol to set those fields to some empty initialised WCSTransform object.

[giordano]

The FITSHeader looks like a dictionary, I was thinking to

• look up the relevant WCS keys in FITSHeader
• feed them into WCSTransform(...)

However, this is a high-level functionality that it's not even clear where it should live (see my message above), I think this is a very low-priority issue, even though an interesting one.

[icweaver]

Hey folks, here's two PRs in the works to try and address this:

1. Convert from FITSHeader to WCSTransform WCS.jl#58. This is a FITSIO extension for WCS.jl. Since FITSHeader --> String already exists in FITSIO.jl and String --> WCSTransform already exists in WCS.jl, this extension just does the small step to go directly from FITSHeader --> WCSTransform

2. WCS header support #228. This handles going the other way from WCSTransform --> FITSHeader

Comments welcome for both!