Use a GPL package in a proprietary licensed software

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IANAL, but I think normally these issues need to be dealt with on a case-by-case basis, and it's always better play on the safe side. It's also important to remember that if there's a chance that someone will take the time to sue you for violating copyright, it also means they should care enough to answer any licensing questions you may have.

I imagine ar_pose's license restrictions come from ARToolKit itself, and on their license page, they summarize the licensing terms by saying:

i.e. your software incorporating or linking to ARToolKit must also be open-source software, licensed under the GPL.

I think the above means that you cannot sell a product that uses the GPL-licensed ARToolKit, or at very least that they might pursue litigation if you do. However, there's good news, because they also have professional and commercial licenses:

In response to demand from toolkit users, the holders of the copyright on much of the ARToolKit version 1.0 - 2.x code have elected to make this code and other substantially advanced ARToolKit and AR code available under proprietary licenses for professional and commercial use by persons for whom the GPL license is not ideal. These license arrangements are managed by ARToolworks, Inc., Seattle, WA, USA. A variety of license types are available at reasonable cost. Please contact ARToolworks, Inc. directly for information on products, license terms, and pricing.

If ARToolKit is the only GPL restriction in that package, then I would suggest:

1. Contact the maintainers of the CCNY ROS packages to privately release a version of their ROS interfaces under a BSD or commercial license.
2. Contact ARToolworks to negotiate a commercial license.

If there are other GPL components, then I would suggest looking for similar solutions.

This is not a direct answer to your question, but a possible improvement and workaround.

I have used both ar_pose (based on ar_toolkit) and ar_track_alvar based on alvar for a project. In my experience the latter one is far better than the former in any terms. Porting your code to use ar_track_alvar will likely take about a couple of hours. The stability, robustness and pose estimation accuracy of alvar library is not the only benefit you'll earn. The ROS driver is BSD licensed and the original library is LGPL* which will make it more appropriate to be used in a commercial product.

• Main difference between GPL & LGPL

I am not a licensing expert in any way, but to my best knowledge the use case you describe is covered by the GPL. You would need to supply source code for you modified GPL code for free, but TCP/IP communications (ROS) with proprietary software should be OK.

I'd be interested in answers that could confirm/refute this in a better verified way.