TRAINING Technology
monitoring the critical latencies of the
motion and visual systems. A significant
difference between the two will not only
cause negative training, the disconnect
could induce pilot sickness.
latencies, or more specifically,
throughput delay – the time between a
pilot’s control input and when it’s felt in
the simulator movement or viewed on the
out-the-window or sensor scene – were
upwards of 150-250 milliseconds prior to
the Air Force c-130 upgrades. Some studies show a simulation throughput delay
of 150 msec is acceptable; other research
recommends 100. Takats indicates they’d
like to optimize those down to about
50-70 milliseconds. “The customer has
seen tremendous improvement in the
product. It’s very subtle, but the general
reaction is that the sim feels better.”
latency takes three separate paths –
motion system, visual system, and instrument panel simulation or stimulation.
When the pilot moves the yoke or stick,
as the case may be, the signal is sent
to the simulator’s aerodynamic model
for position, velocity, and acceleration
changes. every subsystem the signal
passes through for processing adds to
the latency. But the motion/visual synchronization gets the most attention.
“The motion system is pretty fast,
very high frequency, about 5 to 10 milliseconds” (less than a single frame in a 60
hz visual refresh), Takats says. “The visual
is always the long pole in the tent,” The
control inputs must be routed through the
Ig and its graphics processors, where one
of the tradeoffs is how much content the
user wants to see in the scene. “Do you
want to see blades of grass moving in the
wash from propellers? A lot of building
detail? It takes more processing power.
Add scene content, increase latency.”
From the Ig, the signal travels
through the projector. “We can’t control
the latency in the projector. It depends
on what you buy.” Takats says says some
commercial projectors can be around
40-50 msec, while some that are tailored
for simulation or other custom solutions
offer as low as 4-8 msec.
The visual path typically lags 20-30
msec behind the motion path. human
factors specialists suggest a throughput delay difference of 30 msec (about 2
visual frames and a 60 hz system) is not
a problem for pilots. If the visual cannot
keep pace, Takats says the latency in the
motion system can be increased.
18 MS&T MAGAZINE • ISSUE 3/2009
Mountain Village Realism
low density visual scenes may yield inadequate training environments for some
missions, according to MetaVR president
garth Smith. They’ve recently produced a
database of an urban area south of Kabul
with about 500 buildings in a 2 square
kilometer area so the Iowa Air national
guard can train combined forces involving high-speed aircraft, unmanned aerial
vehicles, ground vehicles, and joint terminal attack controllers (JTAcs).
MetaVR’sAfghan village.
Image credit: MetaVR.
“To do really effective training, you
have to train together. And when you’re
trying to cross-reference in urban settings, you have to be very precise.”
new simulator in development by eSg
(elektroniksystem und logistik gmbh,
Munich) to screen helicopter pilot candidates. The FPS-h (
Fliegerpsycholo-gisches System – hubschrauber) simulator will feature concurrent’s linux-based
Imagen visual hardware and Diamond
Visonics’ genesisIg “scenery on the fly”
software. “The luftwaffe wants to be sure
they are getting the right candidates,”
says Ken Jackson, VP development and
special systems for concurrent.
Smith says some urban databases in
use “tend to be simplistic. It’s easy to find
targets. A lot of databases make the terrain flat because it’s easier to simulate. But
that’s not realistic for close air support.”
Training warfighters in an environment
“that accurately represents mountainous
regions with small population centers is
critical.” MetaVR’s Afghan village is set
within mountains and complex terrain of
varying elevation and cave networks.
Imagen’s largest order to date, 32
servers, is from hyundai Rotem for the
K-series Tank Platoon Simulators to be
used by the South Korean Army. hyundai
Rotem developed the K1/K1A1 main battle tanks and family of ground combat
vehicles. each tank simulator includes 8
channels running Presagis’ Vega Prime
visualization software.
The new Afghan database also
“matches the actual footprint of specific
structures.” The urban area is part of
geospecific terrain covering 9,600 square
kilometers. The terrain is also delivered
with correlated semi-automated forces
(SAF) databases.
Databases for high-flying fighter aircraft “used to be less dense” because
high detail was not required. But now
with very high-resolution sensor pods,
even fast movers need to be able to see
the scene at the building level. “The high
flyer needs to see what the ground vehicle driver sees,” Smith adds. “They all
have to see the same database.”
Doing Hard Real Time
The german Air Force plans to use a
Jackson claims Imagen’s strength
derives from concurrent’s “hard real
time” legacy as a simulator host computer developer. “our Ig is not spending
time on operating system latency. In that
magic moment when you hit the joystick,
you want to see what’s happening on the
screen. you don’t want the oS taking a
‘housecleaning’ break.”
concurrent also offers tools for fine-tuning Ig performance. “We work with
nvidia and ATI to make sure their drivers are working their best on our system with no cross-interrupts to slow
things down,” Jackson explains.”And
we can put trace points on the rendering software to know how much time
it’s spending.” The tools will also highlight page faults, “and we can show the
operator how to lock it down in memory
so it never happens again.” ms&t
