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Old 09-26-14, 01:35 PM   #1
nopoe
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Default Unreal Engine 4 sub sim project: Sub^3

Hi everybody,

I recently started working on a project with a friend of mine we're calling Sub^3. We're going to try to make it into a modern version of 688(I) Hunter/Killer.

This project mostly began out of frustration with current sub sims. Specifically, we’re bothered by the fact that the acoustic models kind of suck. There’s a good reason for that in the case of the earlier ones (computing power), but I think that a modern sub sim should really have accurate acoustics.

We’re going to be using a library called USML (Under Sea Modeling library) for our acoustic modeling. It should be suitable for what we want to do. Here’s an image generated by a similar algorithm to show you how awesome they are. They're really hard on the CPU, unfortunately. I have yet to figure out what the minimum requirements are or if I can take advantage of multiple cores, but I expect you will need a modern desktop to run the game. http://oalib.hlsresearch.com/Rays/TLray.jpg

Another issue with using these libraries is that you need a lot of oceanographic data to take advantage of them, so you should also expect a big download (it's already >2.7gb uncompressed). I really dislike high system requirements so I'll do my best to keep everything under control, but my #1 priority is making the best submarine simulator I can, so if it makes sense these requirements could go up.

The main reason for using Unreal Engine 4 is so that we'll actually be able to finish the project. Ogre3d, SDL/OpenGL and various other options were considered. but we ultimately decided UE4 was the only option that let us link with USML (which is written in C++) and would also give us a chance to finish the project. We wouldn't have a chance without extra help otherwise. A lot of work is done for us thanks to UE4, especially in the graphics and networking areas.

Sub^3 is open-source. Unfortunately it's against the Unreal EULA to GPL your projects so we're using the 2-clause BSD license. Here's a link to what we have so far. We'll upload builds when we get something playable.

Right now you can't actually pilot a submarine, but the physics simulations and control loops are working or close to working. In the near future we'll be working on a navigation interface, integrating USML and getting passive sonar working. After that we'll probably start on getting torpedoes working. This project aims to have multiplayer support in the first playable release. The main rationale for that is that writing good submarine AI seems like a really difficult thing to do compared to finding somebody to play with and setting up Hamachi.

One thing we’ll probably need from the community though is the ability to ask questions about submarines so we can understand them well enough to model them in a believable way. Would it be ok to put questions in this thread or is there a better place to do that?

Cheers!
nopoe
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Old 09-27-14, 06:15 AM   #2
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Hi, and welcome!

Looks interesting. But why UE4 and USML? UE4 is very limited for a simulator, the area is limited to 20x20 km (if I'm not mistaken), it is slow, and I just don't like dotnet , and moreover, you have to link it with C++...

And, in my opinion, USML is too heavy for a game (or perhaps I should say "real-time simulation" ). Also, consider the oceanographic data, I doubt you will find it for every point of every ocean, sea, etc. The whole idea of such perfect precision is questionable without it. I'm not even talking that acoustic equations are not perfect themselves. Add classified data on submarines, sensors, etc. to that.
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Old 09-27-14, 11:20 AM   #3
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nice library and all the best for your project!
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Old 09-27-14, 11:23 AM   #4
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sounds great, ill keep an aye on this
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Old 09-27-14, 11:49 AM   #5
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Quote:
Looks interesting. But why UE4 and USML? UE4 is very limited for a simulator, the area is limited to 20x20 km (if I'm not mistaken), it is slow, and I just don't like dotnet , and moreover, you have to link it with C++...
UE4's usual way of dealing with the fact that their world size is, quite frankly, tiny (5km by 5km or something) is world origin rebasing. But that doesn't help when you need to keep the entire world in memory because an anti-ship missile launched 100km away is still a threat. Additionally it gets really complicated when you are doing a multiplayer game.

The simplest way to deal with this issue, scaling down everything except the world, happened to work. I have the luxury of not having to simulate anything remotely small so I managed to scale everything down by 100x. I can now simulate worlds 500km by 500km across, which is much less limiting. I've tested the physics stability at the world edges and it seems exactly the same as the center, so I'm pleased with this solution.

I'm not sure what you mean by not liking .NET though. UE4 uses C# for its build system but that's about it. And linking with C++ is the primary advantage because it lets us use USML.

Regarding slowness, you're basically correct. UE4 is a heavyweight engine, but it made the most sense.

Quote:
And, in my opinion, USML is too heavy for a game (or perhaps I should say "real-time simulation" ). Also, consider the oceanographic data, I doubt you will find it for every point of every ocean, sea, etc. The whole idea of such perfect precision is questionable without it. I'm not even talking that acoustic equations are not perfect themselves. Add classified data on submarines, sensors, etc. to that.
Regarding USML's speed, you're also correct depending on the platform. It's really slow on windows, but it runs about 20x faster than realtime on Linux using a single core. If I gave USML 3 cores, it should theoretically be able to propagate 60 waves at once. It's not necessary to update the propagation losses for far away contacts as often, so that could potentially mean a lot of vessels. I'm working this weekend, but starting around Wednesday I'm going to look at changing the linear algebra backend to something that will let me take advantage of OpenCL devices. Hopefully that will let me get the bulk of the processing onto a GPU or at the very least allow me to use multiple cores with minimal work.

It currently uses uBLAS, which is apparently known for being slow, so even if it doesn't work on a GPU I'd expect the windows performance to meet or exceed the linux performance after I switch. If it does work on the GPU it has the potential to make it all a non-issue.

The oceanographic data I have seems pretty solid, but USML has a built in way of interpolating between nearby data points if there's missing data.

As for why to use USML, the main reason is that it's one of the only pre-existing options out there that isn't in fortran. The alternative is writing my own sorta-correct-but-faster acoustic modeling library or not modeling acoustics at all and just basing detectability on distance, which I'm not interested in. I know for a fact I would never finish my own acoustics modelling project. I don't know enough math or physics.

In addition to that, I think having good acoustic modeling will make the game more fun. The aim isn't to make it extremely true-to-life necessarily, since as you said that's problematic due to classified information. I want a fun game and accurate acoustics is a part of that I think.
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Old 09-27-14, 12:03 PM   #6
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Is that sound engine not more or less a bunch of functions, that is does it really need to be tightly integrated into your application?

In my cold war sub sim project I've currently implemented my own engine, but it is pretty rudimentary...so I might later have a look . It is in .NET, so writing a c++ bridge would be an option....I think there are tools available to autogenerate wrapper.

And concerning .NET....if you have programmed with that framework and its rich set of languages, you do not wanna go back.....it is so 'easy' to write code, running on multi-cores.
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Old 09-27-14, 12:19 PM   #7
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Quote:
Originally Posted by Hawk66 View Post
Is that sound engine not more or less a bunch of functions, that is does it really need to be tightly integrated into your application?

In my cold war sub sim project I've currently implemented my own engine, but it is pretty rudimentary...so I might later have a look . It is in .NET, so writing a c++ bridge would be an option....I think there are tools available to autogenerate wrapper.

And concerning .NET....if you have programmed with that framework and its rich set of languages, you do not wanna go back.....it is so 'easy' to write code, running on multi-cores.
You should be able to write a wrapper for it pretty easily. If I manage to speed it up at all I'll push it to my github and let you know so you can use my version as well. Also if you have trouble building it on windows that you can't figure out feel free to send me an email (listed on my github page). It's not exactly trivial but definitely possible.

This page should list what you need to know: http://oalib.hlsresearch.com/Rays/USML/usml_frontpage

I'm a fan of C#, but for a game I like having most of the work already done for me, which is why UE4 made the most sense. Unity was the other option, but I if I could choose between having to write a wrapper and not having a source license for my engine or not having to write a wrapper and having a source license for my engine, I'm going to pick the latter.
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Old 09-28-14, 12:12 PM   #8
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USML is not designed to run "real-time," though in your case what this means depends on how you're using it.

If you're just using it to control how bright lines are on your sonar display, you should be OK with it producing results every few seconds.

If you're trying to use it to generate actual acoustics (sound), you'll definitely run into problems. For one, it's designed to give more of a qualitative overview of the ocean environment, so it doesn't necessarily provide the kind of detail you'll need to generate the actual sound you'd hear. The fact that it is also slow means it'll be very difficult to generate acoustics without extensive interpolation/extrapolation of the model's output.

Using the eigenrays will pose a big challenge to you as well. Expect the model to generate thousands of eigenrays for a single point-to-point run. How you use those eigenrays will dramatically affect the overall presentation of the ocean, and will be important especially for how multipath effects show up.
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Old 09-28-14, 12:37 PM   #9
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Old 09-29-14, 12:38 AM   #10
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Originally Posted by magicstix View Post
USML is not designed to run "real-time," though in your case what this means depends on how you're using it.

If you're just using it to control how bright lines are on your sonar display, you should be OK with it producing results every few seconds.

If you're trying to use it to generate actual acoustics (sound), you'll definitely run into problems. For one, it's designed to give more of a qualitative overview of the ocean environment, so it doesn't necessarily provide the kind of detail you'll need to generate the actual sound you'd hear. The fact that it is also slow means it'll be very difficult to generate acoustics without extensive interpolation/extrapolation of the model's output.

Using the eigenrays will pose a big challenge to you as well. Expect the model to generate thousands of eigenrays for a single point-to-point run. How you use those eigenrays will dramatically affect the overall presentation of the ocean, and will be important especially for how multipath effects show up.
Yeah, I know it's not a real-time modeling engine, but I think I'll probably be ok. As far as I can tell from the unit test code, it gives you a bunch of propagation losses for the frequencies you propagate. I'm going to propagate a frequency vector and store the propagation losses and approximate travel times on a per-vessel basis. Then the USML worker thread will move on to modeling another vessel's sound. Meanwhile the sonar display will iterate through all vessels taking the most recent propagation loss and then use that, combined with the amount of sound the contact was making in each frequency band n seconds ago to find the "brightness" of the line on the broadband display, where n is the travel time. So if the other vessel makes a ton of noise for a split second, you'll still hear it even if there was no wave propagation happening during that time.

From my tests on Linux I think this is pretty doable real-time on a fast, modern quad core as long as you don't need to update propagation losses too fast and you have a reasonable number of vessels nearby. I've been testing with the malta-movie unit test as my benchmark, which (I think) uses eigenrays so I should be fine.

On Linux it took 4 seconds or so to finish the malta-movie unit test, which included time to load the bathymetry and temperature data from disk (though I removed the saving of the netcdf data). The test itself propagates a wavefront with 90 individual rays for 60 simulated seconds. If you say the average contact distance is going to be 60 seconds away, that means you can update one contact's propagation losses every 4 seconds using one core. Using multiple independent USML worker threads (assuming I can set that up) you can average an update frequency 1/n where n is the number of vessels.

With 20 vessels, which seems like a lot to me, that's one update every 20 seconds. 20 seconds seems like a very long period of time to go without updating propagation losses, but keep in mind the sonar display will still track the sound they've been making during that time. Additionally, that's for contacts that are almost 50 nautical miles away. Even if the two contacts are racing towards each other at 30 knots each they're barely going to cover 600 meters in that time. To put that in perspective, 600m is 0.6% of the total seperation, roughly. That's not going to change their acoustic situation that much. Sound from contacts closer to the sonar array will require (approximately) proportionally less time to propagate. From what I can tell, the complexity per timestep really depends on what the rays are doing in the ocean, but roughly speaking the closer contacts can be updated more frequently.

I'm by no means an expert on submarines, computational acoustics or anything else that this project involves, but I do think I did the benchmarks and the math right.

Like I said, though, it's too slow on windows. Way too slow. And I think OpenCL is probably the wrong choice because there's a lot of overhead associated with it, so I'm currently looking at Eigen as an alternative.

The current status is that most of the stuff in the "ublas" subdirectory is rewritten to use Eigen and I've started moving the rest of the library over. I'm currently puzzling as to how to best handle the seq_vector class. I know it's a pretty big undertaking and stuff, but the project is dead already otherwise so it's worth a shot. If I do get it working I think performance should be as good or better on windows as it was on linux with uBLAS. That's not a small "if" though. It would be really nice if visual studio had better performance...

Last edited by nopoe; 09-29-14 at 01:13 PM.
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Old 09-29-14, 05:38 AM   #11
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Old 09-29-14, 07:31 AM   #12
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Old 10-01-14, 11:48 AM   #13
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Default USML update

Technical details on what I managed to accomplish:

While poking around in the USML codebase I figured out there are faster but more approximate ways to do some of the things that I was doing, so using those I managed to get the average time between updates down to 0.7 seconds per contact at 20nm spread across all cores. Instead of replacing the linear algebra library, I decided to eliminate one very expensive matrix operation and replace it with a bunch of individual scalar operations. That brought computation time per contact down to 0.5 seconds. I'm thinking that's adequate.

These computation times are calculated based on the average time for 4 separate benchmarks to run to completion divided by 4. There's a little more to it than that, but it's important to note a single computation actually takes around 2 seconds, but there are 4 happening at once so you'll get one update every 0.5 seconds on average.

So now all that remains is creating the actual game.
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Old 10-04-14, 11:12 AM   #14
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Quote:
Originally Posted by nopoe View Post
So now all that remains is creating the actual game.
That's a very important point. Usually what I see sinking hobbyist projects like these is focusing on the wrong things too early. Yes, it's good and cool to have a super accurate acoustics model that makes former sub sailors think they're at sea, but if you spend all your time on that early and burn out, where's the rest of the game?

The best thing to do is focus on the fundamentals early on. Get your entity system done, get your network communications done, get a game going before adding the flash and bling. Don't worry about the ocean modeling until you have a sonar display, use 20 log R propagation and get dots stacking on your simulated broadband waterfall first. Playability beats pretty any day.
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Old 10-05-14, 01:36 AM   #15
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Originally Posted by magicstix View Post
That's a very important point. Usually what I see sinking hobbyist projects like these is focusing on the wrong things too early. Yes, it's good and cool to have a super accurate acoustics model that makes former sub sailors think they're at sea, but if you spend all your time on that early and burn out, where's the rest of the game?

The best thing to do is focus on the fundamentals early on. Get your entity system done, get your network communications done, get a game going before adding the flash and bling. Don't worry about the ocean modeling until you have a sonar display, use 20 log R propagation and get dots stacking on your simulated broadband waterfall first. Playability beats pretty any day.
All I was doing is making sure my goal was possible. I'd hate to get something playable without an acoustics model and then realize I was going to need to model all the acoustics myself because the libraries out there weren't fast enough. I simply do not know enough math or physics for that, and it would permanently stall release unless somebody else stepped in and did it for me (unlikely, but it's open source so it could happen). I'd hate to get to that point after a few months of work or more. It's much better to assess all risks up front, especially the ones that have the potential to prevent the project from becoming what I want it to.

Like I said in the original post, we're using Unreal Engine so it already has an entity-component system and the networking code is written for me. I just need to use some preprocessor macros before variables and the engine takes care of the rest.

I've properly finished a few hobby projects before, so I totally understand what you're trying to convey, but benchmarking USML made sense for me. I don't want to make something that isn't as good as what's already available, because then nobody would have any reason to play it.

Unfortunately my graphics card died on me today so I'll need to take a break from the project for however long it takes to get it RMA'd. Maybe a week or two. The unreal engine editor doesn't run on integrated graphics.
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