rfits and edits have two branches each: one that uses Astro::FITS::Header and
one that doesn't. If Astro::FITS::Header is installed it *should* support
duplicate fields and multiple lines as you want -- though there are some
gotchas (A::F::H merges COMMENT fields into one block in the output, for
example).
A::F::H turns multiple COMMENT cards into a single multi-line string in a
single COMMENT hash field, on read. On write the string is broken back up into
COMMENT cards. Same for HISTORY.. You can achieve finer granularity of
control using the non-tied interface: with A::F::H installed the hashref used
as your PDL's header field is a pointer to the tied hash, and you can back out
the underlying object in the usual way (with the "tied" operator).
It sounds as if you might be using the legacy interface that uses Perl hashes
alone...?
(Mobile)
> On Apr 29, 2017, at 12:54 AM, Karl Glazebrook <[email protected]> wrote:
>
> Yes, the FITS standard allows these particular special case duplicate fields,
> but the PDL FITS readers has never supported them. It was done by hashes and
> of course hashes can only have one key. I imagine to get what you want you
> would have to modify Astro::FITS::Header either with special code our to use
> Tie::DxHash (which is probably overkill)
>
> Karl
>
>
>> On 29 Apr 2017, at 3:20 am, ejm <[email protected]> wrote:
>>
>> Hi all,
>>
>> I have a question about PDL::IO::FITS and in particular the methods hdr &
>> gethdr.
>>
>> I've got a Moose script that works fine with PDL::IO::FITS and adds fine the
>> usual FITS fields to a FITS
>> header. The resulting FITS file is read fine by SAOImage and the FITS fields
>> are in the order I want.
>>
>> The problem is with fields that are potential duplicates such as COMMENT and
>> HISTORY.
>>
>> I noticed that PDL::IO::FITS doesn't make use of Tie::DxHash which
>> specifically handles duplicate keys in tied hashes. Nor does
>> Astro::FITS::Header.
>>
>> I also don't see exported in PDL::IO::FITS the methods insert or index from
>> Astro::FITS::Header which might be the right methods to call for adding
>> COMMENT fields.
>>
>> When I create a tied hash using Tie::DxHash and copy over the data returned
>> by gethdr, I get a tied hash with duplicate COMMENT fields in the order I
>> want.
>>
>> I then save the resultant updated FITS header hash using sethdr.
>>
>> But when I view the FITS file in SAOImage for example I see the added fields
>> in alphabetical order, not the tied order they were saved in. I also don't
>> see any COMMENT fields.
>>
>> If I don't use Tie::DxHash, but just add the COMMENT field directly to the
>> tied hash returned by gethdr, I get only 1 COMMENT field in the header, with
>> the last value assigned to it, which makes sense since Tie::DxHash isn't
>> being used. Hence no duplicate keys allowed.
>>
>> What is the recommended way to add multiple COMMENT fields using
>> PDL::IO::FITS ?
>>
>> Thanks,
>>
>> --Ed
>>
>>
>>
>>
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>
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