Computer-generated displays are becoming increasingly popular in aerospace applications. The use of stereo 3-D technology provides an opportunity to present depth perceptions which otherwise might be lacking. In addition, the third dimension could also be used as an additional dimension along which information can be encoded. Historically, the stereo 3-D displays have been used in entertainment, in experimental facilities, and in the handling of hazardous waste. In the last example, the source of the stereo images generally has been remotely controlled television camera pairs. The development of a stereo 3-D pictorial primary flight display used in a flight simulation environment is described. The applicability of stereo 3-D displays for aerospace crew stations to meet the anticipated needs for 2000 to 2020 time frame is investigated. Although, the actual equipment that could be used in an aerospace vehicle is not currently available, the lab research is necessary to determine where stereo 3-D enhances the display of information and how the displays should be formatted

Crittenden, Lucille

Lane, Harold

Nataupsky, Mark

Turner, Timothy L.

English

NASA Technical Reports Server

N90-22955
DEVELOPMENT OF A STEREO 3-D
PICTORIAL PRIMARY FLIGHT DISPLAY
Mark Nataupsky 1
NASA Langley Research Center
Hampton, Virginia
Timothy L. Turner
Harold Lane
Lucille Crittenden
Research Triangle Institute, North Carolina
INTRODUCTION
Computer-generated displays are becoming increasingly popular in aerospace applications.
The use of stereo 3-D technology provides an opportunity to present depth perceptions which oth-
erwise might be lacking. In addition, the third dimension could also be used as an additional
dimension along which information can be encoded.
Historically, the stereo 3-D displays have been used in entertainment, in experimental facil-
ities, and in the handling of hazardous waste. In the last example, the source of the stereo images
generally has been remotely controlled television camera pairs.
This paper describes the development of a stereo 3-D pictorial primary flight display used
in a flight-simulation environment. The purpose of this research is to investigate the applicability
of stereo 3-D displays for aerospace crew stations to meet the anticipated needs of the 2000-2020
time frame. Although the actual equipment that could be used in an aerospace vehicle is not cur-
rently available, the laboratory research is necessary to determine where stereo 3-D enhances the
display of information and how the displays should be formatted.
HARDWARE/SOFTWARE CONFIGURATION
The hardware consists of a VAX 11/780 computer, an Adage 3000 raster programmable
display generator (PDG), and a Stereographics 3-D display stereoscopic system. A FORTRAN
aircraft simulation is used to provide parameters to the display programs residing in the
Adage 3000. The display programs are written in a "C" language known as ICROSS-3000, with
a graphics-enhancement package known as the Real-Time Animation Package (RAP). (RAP is a
proprietary software product developed at the Research Triangle Institute.)
The Stereographics display uses liquid crystal shuttered glasses and specially adapted
hardware which divides each video frame into two fields corresponding to the left- and right-eye
views, each at half the resolution. The PDG outputs a 60-Hz repeat field, 512 x 512 pixel image.
The stereo display system converts this input to a 120-Hz repeat field, 216 x 512 pixel output with
ILt. Col., USAF. Detailed to the NASA Langley Research Center.
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https://ntrs.nasa.gov/search.jsp?R=19900013639 2020-03-19T22:06:48+00:00Z
alternatingleft- andfight-eyefields. Figures1and2 showamonocularversionof thedisplay.
Figure3 showsasimilardisplaywith left- andfight-eyestereoviewsastheywouldappearona
conventional60-Hzmonitor. TheStereographicsystemconvertstheinput shownin figure 3 and
generatesthestereopairssimilar to thosein figures1and2, butwith only half theverticalresolu-
tion. Theliquid crystalshutteredglassesaresynchronizedsothateacheyeseesonly oneof the
stereoviews.
A stereoimagepaircontainstwicetheinformationcontainedin amonocularimage. There-
fore,onasystemwith limited videobandwidth,eitherthevideoframerateor thenumberof lines
mustbereducedwhenstereodisplaysarebeinggenerated.Thecurrentsystemmaintainsframe
rateby halvingthenumberof lines. Flicker,whichwasa problemwith othersystems,is thus
eliminated.Thesystemalsoperformstheconversionof thevideosignal,andthePDGresponds
asif it wereoutputtingits customary60-Hzrepeatfield image.Theliquid crystalshuttertech-
nologyis muchfasterthanthevideoframe-rate-displaycapabilities;therefore,thestereosystem
doesnot imposeanybandwidthlimitations.
DISPLAY FEATURES
The main features of the display are an own-ship symbol, a perspective follow-me target
ship, two different 3-D tracks showing the path of the target ship, a ground grid around the
runway, a pitch grid on both the left and fight sides of the display, and digital readouts for
altitude/heading/airspeed. The digital readouts display the instantaneous values for the own-ship
and the desired preprogrammed flightpath. Because the own-ship remains fixed relative to the
other display elements, an inside-out (i.e., moving horizon) display is represented.
Generating the Stereo 3-D Effect
The display program needs to generate the left- and fight-eye views of the display. Given
distinct x, y locations of each eye, the calculation of the viewing transformations are described by
Foley and Van Dam (ref. 3).
Two parameters are used to control the stereo 3-D effect: zero-parallax distance and inter-
ocular separation. In general, parallax refers to the positional discrepancy in the left- and right-eye
views of a point in the display. The parallax is zero when the corresponding points in each view
occupy the same relative screen location. Points in the display at the zero-parallax distance from
the eye appear to lie in the plane of the screen. Points closer to the pilot than the zero-parallax dis-
tance appear to lie in front of the screen, while points farther from the pilot appear to lie beyond the
screen. In addition, the interocular distance controls the apparent relative depth of objects in the
display. The greater the interocular distance, the more powerful the stereopsis effect. By com-
paring the apparent depth of the target ship with the own-ship symbol, the pilot has an indication of
position error. This stereo 3-D effect reinforces the depth cue provided by the relative size of the
perspective target ship.
When viewing objects in the natural environment, the eyes must perform the separate func-
tions of converging and focusing on a point of interest. In a stereoscopic display, although the
eyes must converge on an object, they focus on the plane of the screen regardless of the apparent
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distance. One requirement of a stereo 3-D display is to minimize that disparity (ref. 4). This is
accomplished by keeping the principal objects near the zero-parallax distance where the focus and
convergence relationship is correct.
After setting the zero-parallax distance at the desired distance from the aircraft to the target
ship, the size of the target ship becomes a distance cue. For example, if the pilot is following too
closely, the target ship appears larger on the screen and projects out of the plane of the screen
towards the pilot. Conversely, if the pilot drops behind the target ship, it appears to shrink in size
and recede into the background. The combination of stereo and size cue serves as an important
error indicator.
In this display, the zero-parallax distance is set to a nominal following distance. The inter-
ocular distance was established empirically at 8 ft. Moving the eyes that far apart is equivalent to
shrinking the scale of the scene proportionally. Such distortions enhance the pilot's ability to per-
ceive the sensations of depth. They are also necessary because of inherent limitations of the hard-
ware. The precision in rendering the left- and right-eye views is limited both by the display reso-
lution and the arithmetic precision of the display processor (i.e., 16-bit f'Lxed point).
If a fixed time lag rather than a fixed distance is desired, the zero-parallax also could be
dynamic. In that case, the zero-parallax distance would be a function of the time lag and the
instantaneous velocity of the target ship.
Within the 3-D display, apparent depth had to be assigned to 2-D symbols such as digital
readouts and the pitch scale. Two possible choices are the zero-parallax distance or the maximum
distance. If they are set at the zero-parallax distance (i.e., drawn with the same left- and right-eye
view), they would be perceived by the pilot as if they were being looked past in order to see the
part of the 3-D display beyond the zero-parallax distance. Earlier informal evaluation has shown
the resulting perception to be disorienting. Instead, by placing the 2-D symbols at the maximum
distance, they appear natural and unobmasive.
Care must be taken when defining the left- and right-eye transformations. Figure 4 illus-
trates two ways of conceptualizing the transformations. In figure 4a, the views are converged by
rotation of the viewing pyramid. In figure 4b the viewing pyramids are sheared. The latter
approach is preferred, as the projection planes in each view remain parallel. Achieving conver-
gence by rotation creates artifacts which can not only cause eye fatigue, but also can interfere with
the pilot's perception of depth (ref. 4). Although the rotation method is easier to implement, the
shearing approach has become the standard in 3-D graphics software (refs. 1 and 2).
Own-Ship Symbol
Figure 5 shows the evolution of the own-ship symbol. The original configuration, fig-
ure 5a, presented the pilot with two problems. First, it was impossible to perceptually fuse the
right- and left-eye viewpoints to form the 3-D image. This fusion problem was surprising,
because the signposts also were made of single, straight lines, but there was no problem with their
visual fusion. An additional problem was that the own-ship symbol tended to "get lost" in the
display. The signpost symbol was constructed of perpendicular horizontal and vertical lines; the
same was true of the own-ship symbol. Therefore, there were many instances in which the own-
ship symbol would overlay the signposts and could not be perceived.
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In orderto increasethepilot's ability to perceivetheown-shipsymbol,thecenterslanted
linesweredrawnasshownin figure5b. Althoughtheability toperceivethesymbolwasgreatly
increased,therewasstill theproblemof inability to visuallyfusethestereo3-D image.
Figure5cwasoriginally constructedto furtherenhancethepilot'sability to perceive the
own-ship symbol; it worked. A serendipitous benefit was that the symbol now visually fused. At
this time there is no theoretical explanation for the fusion phenomena.
INITIAL RESEARCH
The initial research with the display will be a study of recovery from flightpath offset.
Pilots will be initiated on the nominal flightpath. After 2 sec, they suddenly will experience a
flightpath offset. They will be required to make the stick input to rejoin the nominal flightpath.
Visually evoked potentials will be triggered from the sudden flightpath offset. In addition, reaction
times, response accuracy, and a projected workload estimate also will be recorded. The Subjective
Workload Assessment Technique (SWAT) will be used for the workload estimate (refs. 5 and 6).
A test for stereoscopic acuity will be administered prior to data collection. Recent anecdotal
evidence indicated that some subjects tend to lose the ability to use the stereoscopic cue after
prolonged exposure to it. Therefore, stereoscopic acuity also will be measured immediately after a
long series of trials with the stereo 3-D cues.
In addition to using stereo 3-D or monocular cues as an independent variable, the inclusion
or exclusion of the target ship will be the second independent variable. The last independent vari-
able will be the pathway. There either will be the signpost or a monorail pathway for the subjects
to follow.
FUTURE RESEARCH
The initial research will use the stereo 3-D cues to represent geographic information. In the
"real world," objects axe geographically separated by space, and the displays will attempt to create
the perception of that geographic separation.
In contrast, one line of future research will use the third dimension as a dimension to
encode new information for the pilot. For example, presume that there is a pictorial display which
is entirely in the plane of the screen and that depth perception is simulated with monocular cues
such as linear perspective. If a pilot were using that display in a current aircraft, and if the airspeed
were to get too low, an audio display (i.e., a horn) would sound. The audio display is an alerting
display, and the pilot must know to then look at the visual display for speed.
However, part of the pictorial display is a box with digital readouts for instantaneous actual
and desired airspeed. Using the same airspeed error example, the box with the airspeed would
modulate in the third dimension (i.e., along the z-axis) as the alerting cue instead of using the audio
cue as the alerting cue. In this manner, new information would be presented to the subjects in the
third dimension.
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Fromahumanfactorsperspective,that is a potential way of decreasing the total number of
cockpit displays and also to make the alerting cues more nearly intuitively obvious. There are
many research questions to be addressed. First, can it be demonstrated that the proposed use of
stereo 3-D is quantifiably better than the use of audio alerting cues? Some of the other questions
concern the rate and perceived depth of modulation in the third dimension. For example, should
the rate or perceived depth of modulation be proportional to the amount of error? Should the mod-
ulation only be from the plane of the screen towards the pilot or should it also modulate from the
plane of the screen away from the pilot?
Other uses of stereo 3-D also are possible. The "natural" use of stereo 3-D is to represent
the 3-D geography. Part of the true test of the technology will be to go beyond that approach and
determine if there are more effective applications.
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REFERENCES
. American National Standards Institute. Draft Proposed American National Standard Program-
mer's Hierarchical Interactive Graphics System. Prepared by Technical Committee X3H3 -
Computer Graphics. New York: ANSI, 1985.
2. Association for Computing Machinery. Status Report of the Graphics Standards Planning
Committee. Computer Graphics, Vol. 13, No. 3, Aug. 1979.
3. Foley, James D. and Van Dam, Andries. Fundamentals of Interactive Computer Graphics.
Reading, MA: Addison-Wesley, 1982. Reprinted with corrections, July 1984.
4. 3-D Display Handbook for Stereoscopic Computer Graphics. San Rafael: Stereographics
Corporation, 1984.
. Reid, Gary B., Shingledecker, Clark A., and Eggemeier, F. Thomas. Application of
Conjoint Measurement to Workload. proceedings of the Human Factors Society-25th
Annual Meeting. Santa Monica, CA: Human Factors Society. 1981a.
. Reid, Gary B., Shingledecker, Clark A., and Eggemeier, F. Thomas. Development of
Multidimensional Subjective Measures of Workload. Proceedings of the International
Conference on Cybernetics and Society, IEEE Systems, Man and Cybernetics Society.
1981b.
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ORIGINM. PP_r2k" f_
OF POOR QUALITY
Figure 1.- Monocular "monorail" display.
Figure 2.- Monocular "signpost" display.
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ORIGINAL PAGE IS
OF_ POOR QUALIFY
Figure 3.- Stereo display as seen on a conventional CRT.
(a) (b)
Figure 4.- Generation of stereo pairs by eye rotation (a); generation of pairs by shearing the view-
ing pyramid (b).
II V ' \_/_
v
(a) (b) (c}
Figure 5.- Evolution of own-ship symbol: Stereo pairs for (a) and (b) would not visually fuse;
(c) would visually fuse.
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