How to handle disparate DIS versions

Felix Rodriguez

Now that VR-Link 5.0 is out and we have added support for DIS Version 7, you might have questions about compatibility between DIS versions and VR-Link. In a nutshell, if everyone is using VR-Link 5.0, there will be no compatibility problems. If you have systems not using VR-Link, or using an older version of VR-Link, then you might have some situations arise.

DIS Version 7 is not fully backwards compatible with previous versions of DIS. If you are sending DIS 7 PDUs, there is no guarantee that the other systems in your exercise will be able to read them. For this reason, by default, VR-Link 5.0 still sends DIS version 6 PDUs. This means that upgrading to VR-Link 5.0 will not suddenly make your exercise incompatible.

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Speed Up VR-Link Performance for HLA 1516 and HLA Evolved

Douglas Wood

Each HLA object must have an object name that is unique throughout the federation execution. When an object is registered, the federate can provide a name or let the RTI supply an object name. In the HLA 1.3 specification, when the federate supplies the name, it is up to the federate to make sure that the name is unique. If it isn’t, the RTI throws an exception. The HLA 1516 specification lets you reserve names to ensure that they are unique.

By default, the VR-Link publishers perform name reservation and object reservation at the same time - when the publisher is created. The name reservation process requires a round trip handshake between the local RTI component (LRC) and the rtiexec. Therefore, performing it just before an object is registered can delay the object registration process. If the federate is simulating a limited number of objects that are created at start up, this overhead is negligible. However, if the federate is creating many 100s of objects or if an object is being created in a time critical fashion (say a missile fly out), the delay caused by name reservation can become significant. One way to avoid the name reservation delay is to perform the name reservations ahead of time before the objects are registered. VR-Link can do this.

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VR-Link Adds New Feature to Prevent Mismatched RTI Versions

Matt Figueroa

When working in an environment with multiple compiler versions of our MÄK RTI installed, it can sometimes be tricky to remember which RTI you have your environment variable pointing to. With the release of VR-Link 4.0.7, we introduced a new “DtVlRtiMismatchException.” An exception in C++ is a way to handle certain outlying situations, like runtime errors, which can lead to program crashes. This new DtVlRtiMismatchException is an exception that VR-Link throws if it finds that the RTI is an incompatible compiler version. When the exception is thrown, a catch is needed to handle it. A catch statement is some C++ code that triggers when a certain exception is caught. This DtVlRtiMismatch-Exception is thrown when making an exercise connection, so adding a catch after creating a connection is a great way to avoid, what are often, vague issues caused by a mismatched RTI compiler version. (continued...)

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VR-Link for Unity

Len Granowetter

We are almost ready to release our beta version of VR-Link for Unity - an HLA/DIS Interoperability module for the Unity Engine!  The official 1.0 release is scheduled for late February.  Meanwhile, you can see a quick demo video here.

On the right, you'll see a helicopter flying a route in VR-Forces. And on the left, you'll see that same helicopter being reflected in real-time into a Unity-based sample application - over HLA through the new VR-Link for Unity asset.  For this demo, we used Unity's well-known "bootcamp" sample terrain, which we also loaded into VR-Forces by exporting it as a height field and image.  And through VR-Link for Unity's model-mapping GUI, we mapped the HLA entity type to a pre-existing Unity helicopter asset.

VR-Link for Unity gives you access to HLA/DIS objects and interactions directly from Unity's standard C# scripting and development environment, so that your Unity applications become natively HLA and DIS compliant.  But since the module is built on our traditional C++ VR-Link libraries, it supports all the various flavors of HLA and DIS and works with any RTI that conforms to the appropriate HLA standards.  You can also leverage VR-Link's FOM mapping capability to support custom HLA FOMs.  If you're building M&S applications on the Unity Engine, and are interested in DIS/HLA interoperability, we'd love to hear from you.  If you are interested in participating in our beta program, or even just willing to help by describing some of your Unity-based projects, please drop us a note at unity@mak.com!

We are almost ready to release our beta version of VR-Link for Unity - an HLA/DIS Interoperability module for the Unity Engine!  The official 1.0 release is scheduled for late February.  Meanwhile, you can see a quick demo video here: ftp://ftp.mak.com/VR-LinkForUnity.mp4
On the right, you'll see a helicopter flying a route in VR-Forces. And on the left, you'll see that same helicopter being reflected in real-time into a Unity-based sample application - over HLA through the new VR-Link for Unity asset.  For this demo, we used Unity's well-known "bootcamp" sample terrain, which we also loaded into VR-Forces by exporting it as a height field and image.  And through VR-Link for Unity's model-mapping GUI, we mapped the HLA entity type to a pre-existing Unity helicopter asset.

VR-Link for Unity gives you access to HLA/DIS objects and interactions directly from Unity's standard C# scripting and development environment, so that your Unity applications become natively HLA and DIS compliant.  But since the module is built on our traditional C++ VR-Link libraries, it supports all the various flavors of HLA and DIS and works with any RTI that conforms to the appropriate HLA standards.  You can also leverage VR-Link's FOM mapping capability to support custom HLA FOMs.  If you're building M&S applications on the Unity Engine, and are interested in DIS/HLA interoperability, we'd love to hear from you.  If you are interested in participating in our beta program, or even just willing to help by describing some of your Unity-based projects, please drop us a note at unity@mak.com!
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Tech Tip - Speed Up VR-Link Performance for HLA 1516 and HLA Evolved

Douglas Wood

Each HLA object must have an object name that is unique throughout the federation execution. When an object is registered, the federate can provide a name or let the RTI supply an object name. In the HLA 1.3 specification, when the federate supplies the name, it is up to the federate to make sure that the name is unique. If it isn’t, the RTI throws an exception. The HLA 1516 specification lets you reserve names to ensure that they are unique.

By default, the VR-Link publishers perform name reservation and object reservation at the same time - when the publisher is created. The name reservation process requires a round trip handshake between the local RTI component (LRC) and the rtiexec. Therefore, performing it just before an object is registered can delay the object registration process. If the federate is simulating a limited number of objects that are created at start up, this overhead is negligible. However, if the federate is creating many 100s of objects or if an object is being created in a time critical fashion (say a missile fly out), the delay caused by name reservation can become significant. One way to avoid the name reservation delay is to perform the name reservations ahead of time before the objects are registered. VR-Link can do this. (continued...)

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Greetings from ATCA

Bob Holcomb

The weather in Atlantic city is definitely IFR conditions ("Instrument Flight Rules" - or for us recovering army helicopter pilots, "I Follow Roads"). There's zero visibility and clouds all the way down to the surface. I'm not the least bit worried though, I'm at the Air Traffic Controller's Technical Symposium with a large number people who are used to landing aircraft of any size in these conditions.

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RTI 4.0.4, VR-Link 4.0.3, and the HLA Evolved API

Morgan Moretz

By Aaron DuBois - The MAK RTI version 4.0 was released on the same day that IEEE officially released the IEEE 1516-2010 standard, otherwise known as HLA Evolved. We were very excited to be able to fully support the new version of HLA from the very first day the standard was out. The down side, however, is that we did all of our development for RTI 4.0 before the standard was finalized, and even at the very end there were minor tweaks happening. Unfortunately we failed to capture the very last change made to the C++ API. As a result, versions 4.0-4.0.3 of the MAK RTI were built against a nearly-final version of the C++ headers, which means that those versions are not quite compatible with the final version of the specification. The new release of RTI 4.0.4 fixes this, and is now built against the final version of the header files.

The final change that was not included in the previous RTI versions was related to a defect in one of the final draft versions of the specification. We actually wrote about this defect in a previous blog post. The problem was with the createFederationExecution RTIambassador methods. There were three variations of this method, each with different input parameters. Some of these parameters contained default values, and as a result there was an ambiguity between two of the variations. We mistakenly thought that there hadn’t been time to get a fix for this ambiguity into the spec, but apparently it did make it in after all. The third variation was renamed to createFederationExecutionWithMIM.

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Our Windows MSVC 10 Plans (and Windows Compiler Compatibility II)

While we don't have firm dates picked for supporting Windows MSVC10 with all MAK products we are planning to roll out support for this new compiler across our product line throughout the year. Today I wanted to provide some details about our thinking, as well as describe how we want to handle the notorious issue regarding SCL and HID compiler flags (see:Windows Compiler Compatibility).

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RTI 4.0 and VR-Link 4.0 Status Update

Today I just wanted to provide a status update on our upcoming MAK RTI 4.0 release, and the corresponding VR-Link 4.0 release .  These releases will add support for HLA Evolved to each product. As most of you know, HLA Evolved is the latest version of the IEEE 1516 standard which was released this spring.

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