[OSGeo-Standards] Please review: Open Letter asking to avoid format fragmentation in LiDAR standards

[Sebastiaan Couwenberg]

On 04/11/2015 01:19 PM, Even Rouault wrote:
> Le samedi 11 avril 2015 12:18:39, Sebastiaan Couwenberg a écrit :
>> On 04/11/2015 09:24 AM, Cameron Shorter wrote:
>>> I forgot to share URL:
>>> http://wiki.osgeo.org/wiki/LIDAR_Format_Letter
>>
>> Are you aware of the legal issue in LASzip which likely contributed to
>> ESRI developing their own alternative?
>>
>> LASzip contains code from the FastAC algorithm which allows distribution
>> but not modification.
>>
>> The FastAC license is therefor incompatible with the LGPL-2.1+ license
>> used for LASzip which guarantees the right to modification.
> 
> I believed the LGPL only guarantees the right to modification to the source 
> code that is licenced under LGPL, or am I wrong ? LGPL can (and does) put 
> constraints on code that uses it, but why/how could it put constraints on code 
> it uses ? 

The LGPL-2.1+ [1] defines a library as follows:

"
 A "library" means a collection of software functions and/or data
 prepared so as to be conveniently linked with application programs
 (which use some of those functions and data) to form executables.

 The "Library", below, refers to any such software library or work
 which has been distributed under these terms.  A "work based on the
 Library" means either the Library or any derivative work under
 copyright law: that is to say, a work containing the Library or a
 portion of it, either verbatim or with modifications and/or translated
 straightforwardly into another language.  (Hereinafter, translation is
 included without limitation in the term "modification".)
"

[1] http://spdx.org/licenses/LGPL-2.1+

The FastAC code in LASzip is part of the "collection of software
functions" and therefor considered integral part of the library.

The LGPL guarantees the right to modify "any portion" of the library:

"
 2. You may modify your copy or copies of the Library or any portion
 of it, thus forming a work based on the Library, and copy and
 distribute such modifications or work under the terms of Section 1
 above, provided that you also meet all of these conditions:

    a) The modified work must itself be a software library.

    b) You must cause the files modified to carry prominent notices
    stating that you changed the files and the date of any change.

    c) You must cause the whole of the work to be licensed at no
    charge to all third parties under the terms of this License.

    d) If a facility in the modified Library refers to a function or a
    table of data to be supplied by an application program that uses
    the facility, other than as an argument passed when the facility
    is invoked, then you must make a good faith effort to ensure that,
    in the event an application does not supply such function or
    table, the facility still operates, and performs whatever part of
    its purpose remains meaningful.

    (For example, a function in a library to compute square roots has
    a purpose that is entirely well-defined independent of the
    application.  Therefore, Subsection 2d requires that any
    application-supplied function or table used by this function must
    be optional: if the application does not supply it, the square
    root function must still compute square roots.)
"

The license for the FastAC portion does not allow modification making it
incompatible with LGPL.

The changes made to the FastAC source code included in LASzip can also
be considered a violation of the FastAC license. But since those changes
are quite minimal it can be argued that the FastAC terms do not apply,
only a court ruling can settle this argument.

Since the FastAC authors would like their work to be used in open source
projects they are unlikely to make a case about the modifications made
to their code in LASzip, but it's entirely within their rights under the
current license terms.

The FastAC terms make LASzip undistributable because the LGPL gives
permissions to recipients of the library to modify it and disallows
restricting these rights:

"
 10. Each time you redistribute the Library (or any work based on the
 Library), the recipient automatically receives a license from the
 original licensor to copy, distribute, link with or modify the Library
 subject to these terms and conditions.  You may not impose any further
 restrictions on the recipients' exercise of the rights granted herein.
 You are not responsible for enforcing compliance by third parties with
 this License.
"

The FastAC license does restrict these rights in violation of this clause.

> Similar situation: I can write GPL/LGPL code that works on Windows and links 
> against Windows system libraries, which don't give right to modification, but 
> it doesn't invalidate the fact that I chose GPL/LGPL license for my code and 
> doesn't prevent anyone using it under their terms.

The license for the Windows libraries are leading in this example, if
their license terms contains a clause like the LGPL about a "work that
uses the Library" those terms are applicable to the GPL/LGPL code that
use the Windows libraries.

> For Debian, I can understand that it doesn't want to distribute code licensed 
> with free license that uses code with a not-free license. But from the point 
> of view of a proprietary software editor, if you don't need to make any 
> modification to the FastAC code, what's the issue ?

As explained above the LGPL allows modification of "any portion", which
in the case of LASzip is not applicable, because the FastAC portion does
not allow modification. This is the root of the problem.

A proprietary software vendor needs to comply with the Free Software
licenses of the works it includes in their product. GPL licensed works
are out of the question because inclusion of only portions of the code
makes their entire product the GPL code is included in a derivative work
to which the terms of the GPL apply.

The proprietary software vendor can only include LGPL licensed works
because only linking to the library does not make their product a
derivative work of the library. If they make modifications to the LGPL
licensed work, those modifications do fall under the LGPL license and
therefore require source code for the modification be made available.

The current FastAC license doesn't allow that portion to be modified,
preventing anyone from making improvements. If the FastAC code was
freely licensed, ESRI could have improved the algorithm instead of being
forced to develope an alternative for example.

Kind Regards,

Bas

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