[AstroPy] Healpy

Mon Oct 5 15:24:00 EDT 2015

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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