[AstroPy] Healpy

[Thomas Robitaille]

Hi Leo,

Yes, this would be great - and note that affiliated packages don't have
to be BSD (in fact, that was one of the reasons to have affiliated
packages - to allow different licenses if needed).

Cheers,
Tom

Singer, Leo P. (GSFC-661.0)[OAK RIDGE ASSOCIATED UNIVERSITIES (ORAU)] wrote:
> Hi,
> 
> I help out a little with Healpy, mainly on bug fixes and software packaging. Healpy has a kind of specialized build process because the underlying healpix_cxx library uses some bleeding edge C++ and runtime features. I think that the Healpy developers would be delighted to have some help making Healpy an Astropy-affiliated package. At a technical level, wouldn't that be a step closer to actual integration with Astropy?
> 
> Thanks,
> Leo P. Singer
> NASA Postdoctoral Program Fellow
> Goddard Space Flight Center
> 
>> On Oct 5, 2015, at 14:48, Thomas Robitaille <thomas.robitaille at gmail.com> wrote:
>>
>> Hi Nathan and others,
>>
>> I already tried to contact the Free Software Foundation about this kind
>> of question (they have a special address for licensing questions), but
>> got no reply.
>>
>> In these kinds of discussion, people often claim to know the answer (one
>> way or another), but none of us are lawyers, and the truth is that the
>> term 'derivative work' as used in GPL is poorly defined. There is a
>> whole section in the GPL Wikipedia article regarding statically linking
>> and dynamically linking against a GPL library:
>>
>> https://en.wikipedia.org/wiki/GNU_General_Public_License#Linking_and_derived_works
>>
>> with different point of views rather than a single interpretation. I
>> think there really is no clear answer and we won't know until it's
>> tested in court. Since this is not a solved issue for linking, the
>> situation is even fuzzier for importing Python packages.
>>
>> As a side note, I did contact the HEALPIX developers, and asked if they
>> could re-license under LGPL (or other) to avoid these issues, and one of
>> the developers answered and actually argued that healpy and any package
>> using it could actually be BSD as long as they don't modify HEALPIX, and
>> that they wouldn't seriously consider a change of license unless we can
>> definitely prove that this is an issue when importing Python modules.
>> All they want to do is prevent linking with proprietary codes (so I very
>> much doubt they will sue us).
>>
>> Regarding my email about reproject, I did not say that users should
>> abide by the GPL only if they use the healpy-based functionality, but if
>> they *install* healpy. After all, if a user installs the reproject
>> package into an empty Python environment with just Astropy, and does not
>> have healpy installed, there is no reason they need to use that code and
>> obey the GPL just because my code contains the words 'import healpy'. In
>> a way, I am dual-licensing the software - if healpy is not installed,
>> people can use it under the BSD license, and if healpy is installed,
>> they should follow the GPL.
>>
>> In any case, the issue will be moot soon. WCSLIB includes an
>> implementation of HEALPIX which I plan to swtich to as soon as possible.
>>
>> Cheers,
>> Tom
>>
>> Nathan Goldbaum wrote:
>>> On Sat, Oct 3, 2015 at 2:46 AM, Thomas Robitaille
>>>> wrote:
>>>    Hi Emil,
>>>
>>>    The 'reproject' Astropy-affiliated package provides a way to easily
>>>    reproject images using Healpy in addition to astropy.wcs:
>>>
>>>    http://reproject.readthedocs.org/en/stable/
>>>
>>>    The functionality with Healpy is optional, so the package is normally
>>>    BSD-licensed, but if you do install Healpy, then as indicated here:
>>>
>>>    http://reproject.readthedocs.org/en/stable/healpix.html
>>>
>>>    you have to abide by the GPL license instead.
>>>
>>>
>>> Hi Tom,
>>>
>>> I don't want to stir up any problems for you, but I don't understand how
>>> this works legally.
>>>
>>> You're distributing code that imports healpy. Even if it's "optional"
>>> functionality, the code that imports healpy is being distributed under a
>>> BSD license. As far as I understand it, the intent of the user doesn't
>>> matter for the licensing, all that matters is the license the code is
>>> distributed under.
>>>
>>> I'd strongly urge you to contact e.g. debian-legal or the software
>>> freedom conservancy about this to get an opinion from an expert. I
>>> suspect your only legal recourses here are either to no longer import
>>> healpy in the reproject package or relicense reproject under a GPLv2
>>> compatible license.
>>> -Nathan
>>>
>>>
>>>    Cheers,
>>>    Tom
>>>
>>>    Emil Lenc wrote:
>>>> Hi All,
>>>>
>>>> I was wondering if there were any plans to incorporate healpy (the
>>>    python interface to the HEALPIX library) into astropy? I often work
>>>    between HEALPIX and FITS format images and it would be really
>>>    convenient to have these two common formats available within the
>>>    same package.
>>>> Cheers,
>>>>
>>>> Emil.
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