When a Helmet-Mounted Display (HMD) system is used in an aircraft cockpit, the usual intent is to overlay symbols or images in the display on their real-world object counterparts. The HMD system determines a pointing angle (in aircraft coordinates) to the real-world object. This pointing angle is sent to the Mission Computer (MC) for use by other aircraft systems and is used by the HMD to position symbology in the HMD image. The accuracy of the HMD is defined as the error of the pointing angle sent to the MC versus the real-world angle to the object. This error is usually given in terms of milli-radians (mrad). Note that having the symbol in the HMD image overlay the corresponding object in the real world does not necessarily ensure an accurate pointing angle. One example of HMD use is to position an aiming cross in the display over an aircraft in the sky. The pointing angle to that aircraft is sent via the MC to another sensor (radar, missile, targeting pod) which then locks onto that aircraft or object. The accuracy requirement is to get the other sensor pointed at an angle to detect the same aircraft. There are aircraft integration issues to ensure target acquisition, but these will not be covered in this paper. One component of the HMD system is a tracker system, and the tracker system's accuracy is often looked at as the HMD accuracy. However, the accuracy of the tracker system is only one piece of the total HMD system accuracy, and as trackers get better, they may not even be the largest error component. This paper identifies the various error components of the HMD system installed in the aircraft cockpit and discusses the techniques used for minimizing errors and improving accuracy.
Different aircraft in different services and countries have their own set of symbology they want displayed on their HMD. Even as flight symbolgy is standardized, there will still be some differences for types of aircraft, different weapons, different sensors, and different countries. As an HMD supplier, we want to provide a system that can be used across all these applications with no changes in the system, including no changes in the software. This HMD system must also provide the flexibility to accommodate new symbology as it is developed over the years, again, with no change in the HMD software. VSI has developed their HMD software to accommodate F-15, F- 16, F-18, and F-22 symbology sets for the Joint Helmet Mounted Cueing System. It also has the flexibility to accommodate the aircraft types and services of the Joint Strike Fighter: Conventional Takeoff and Landing variant for the USAF, Carrier-based Variant for the USN, and the Short Takeoff and Vertical Landing variant for the USMC and U.K. Royal Navy and Air Force. The key to this flexibility is the interface definition. The interface parameters are established at power-on with the download of an interface definition data set. This data set is used to interpret symbology commands from the aircraft OFP during operation and provide graphic commands to the HMD software. This presentation will define the graphics commands, provide an example of how the interface definition data set is defined, and then show how symbology commands produce a display.
Conference Committee Involvement (1)
Helmet- and Head-Mounted Displays IX: Technologies and Applications
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.