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Obtaining YAsim codebase for Unity simulator?

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Obtaining YAsim codebase for Unity simulator?

Postby UnknownTarget » Mon Feb 21, 2022 5:26 am

I hope this is the right place. I'm developing a Unity based flight sim and was just wondering if there was a way to get YAsim in it for a commercial project? Thank you!
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Re: Obtaining YAsim codebase for Unity simulator?

Postby Thorsten » Mon Feb 21, 2022 7:45 am

Provided you're willing to license your project GPL 2+ and make it openly accessible yes, otherwise no.
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Re: Obtaining YAsim codebase for Unity simulator?

Postby UnknownTarget » Mon Feb 21, 2022 1:46 pm

We can't expose unity's code but we could distribute the integration. Is that possible?
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Re: Obtaining YAsim codebase for Unity simulator?

Postby Hooray » Mon Feb 21, 2022 1:50 pm

please read up on the license of the involved components (YASim is actually a standalone program and could be used as such, the FSF has a ton of FAQs exactly on that matter, this forum is a poor replacement for looking up those)

both, YASim and JSBSim, can be used standalone (i.e. in separate address/process spaces), at which point you would be circumventing the (L)GPL automatically.
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Re: Obtaining YAsim codebase for Unity simulator?

Postby S&J » Mon Feb 21, 2022 2:15 pm

No he just needs to make a copy of the GPL code available 'if' anyone asks.
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Re: Obtaining YAsim codebase for Unity simulator?

Postby UnknownTarget » Mon Feb 21, 2022 2:25 pm

I've been doing a lot of digging and can't find the source for YaSim and it doesn't have a separate easy to find page. Would you guys mind pointing me in the right direction please?

I'm not a developer, I'm an artist so I'm sorry if all this seems a bit elementary.

Thanks for the tip on the FAQ: https://wiki.flightgear.org/Frequently_asked_questions

When you say circumventing it, do you mean that in a good way or a bad way? i.e. are we running a separate program in the background and thus we're not in any danger of licensing issues?

Thanks for the clarification S&J. :)

Thank you both for your time!
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Re: Obtaining YAsim codebase for Unity simulator?

Postby Hooray » Mon Feb 21, 2022 2:46 pm

You should probably reach out to the software folks you are working with, i.e. developers/software engineers or programmers and "coders", the point being - this may all sound pretty fancy and sophisticated, but someone with the corresponding background can certainly help you understand what the FSF/(L)GPL expect you to do when you're using an (L)GPL'ed program.

Also, S&J's comments are unfortunately not being helpful either, since they're at best incomplete and depend highly on the given context.
So you really need to get someone involved familiar with the coding side of things and with the corresponding legalese.

The bottom line being, if you are going to use certain open source software with closed-source/proprietary software, you're becoming subject to the terms of that license, which is why it's best to avoid that scenario in a proprietary/commercial project. Basically, you could also search the forum/wiki for "unity" specifically and you will see that this has been previously done, but it all depends highly on your use-case/context, it could be a no-brainer or it can open a huge can of -legal- worms.

Without further context, the best advice at this point is to look up the definition of so called "tight coupling" and interfacing at "arm's length" - at that point, you will understand that using a separate open source binary with an interfacing mechanism (network, sockets, IPC etc) will isolate you from all legal troubles, unless you happen to be subect to the Affero GPL.

Again, all this can be done in a safe and legal way, but you need to have people involved who know what they're doing - and there's nothing scandalous about it either.
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Re: Obtaining YAsim codebase for Unity simulator?

Postby Thorsten » Mon Feb 21, 2022 6:38 pm

YASim is actually a standalone program and could be used as such,


You sure about that? My understanding is that YaSim has a standalone mode, however that only does the coefficient-determination (so you can kinda tune the FDM without having to fire-up the full simulator) - I've never heard of a standalone mode for flight with YaSim.
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Re: Obtaining YAsim codebase for Unity simulator?

Postby Hooray » Mon Feb 21, 2022 7:48 pm

admittedly, it's meanwhile 20 years old (so...), but Andy Ross actually came up with Nasal (Nasl at the time) and yasim for one of his hobby projects, and at the time, the original licensing was rather permissive compared to the GPL used by FlightGear these days.

If in doubt, the people interested in more details (using YASim in a closed-source/proprietary context), would be well-advised to read up on the history of the corresponding components and/or reach out to Andy Ross himself. I am definitely not trying to make statements on his behalf.

That being said, YASim has definitely been used outside FlightGear - and internally, FlightGear uses a so called "FDMShell" mechanism to integrate these two FDMs in a compatible fashion, so someone wanting to use YASim outside FG, could just as well replicate this layer and to come up with a separate binary (address/process space) and use some form of IPC to do what they want to do, without being bound by the terms of the L/GPL.

(again, it's all been done before, and admittedly many things (statements, comments and code) got lost over the years (decades), it seems most of the archives dating back to pre 2002, also are no longer functional)
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Re: Obtaining YAsim codebase for Unity simulator?

Postby S&J » Mon Feb 21, 2022 7:59 pm

Being 'stand alone' is the very essence of being a 'separate piece of work'

I wouldn't worry as you wouldn't be the first to use these type of separate 'physics engine' programs within a sim... Take a look at Ourerra.
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Re: Obtaining YAsim codebase for Unity simulator?

Postby Thorsten » Tue Feb 22, 2022 8:07 am

and at the time, the original licensing was rather permissive compared to the GPL used by FlightGear these days.


That may or may not be the case, but if the question is posed to the FG project, the license to adhere to is GPL and the YaSim code is what it is on the repository. If there's another source available with different capabilities and different license, the question should be answered there.
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Re: Obtaining YAsim codebase for Unity simulator?

Postby erik » Tue Feb 22, 2022 12:55 pm

If Nasal is any indication then it was released under the GPLv.2:
https://github.com/andyross/nasal/blob/master/COPYING

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