DIGITAL EQUIPMENT COMPUTER USERS SOCIETY A STEREOSCOPE DISPLAY FOR ON-LINE MONITORING OF SIMULATED TERMINAL ENGAGEMENTS Psychology Group M.1. T. Li n col n La b 0 ratory, Lexi ngto n , Mass. Thisarticlewas extracted from Technical Note 1965-58 pre­ of computer analysis. pared by Lincoln Laboratory under Electronic Systems Divi­ Moreover, on-I ine analysis has a unique advantage: the sion Contract AF19 (628)-5167. analyst may become an active participant in the process. It describes a stereoscopic, dynamic display of reentry bodies. When it reaches a given point, the program may display rel­ A simulation program on an IBM 7094 generates information evant information, rei inquish control to the analyst, and for the display and feeds it to a PDP-1 computer. The PDP-1 wait for orders. It is not difficult to imagine instances in drives a Type 340 CRT display which is viewed through a which this kind of facility would be of great value, for ex­ spec ial device by a systems analyst. The reasons for this ample, in the developmentofnew procedures of data analysis project are threefold: it is part of a larger effort to evaluate or in the invention of new system doctrine. techniques for on-line control of large computer programs A breadboard computer and display system for on-I ine anal­ that simulate systems and analyze systems data; it is intended ysis of systems is being prepared to test the val idity of these as a test of the feasibil ity of generating on commercial equip­ ideas. No prototype equipment or programs are being de­ ment a display that will give an immediate perception of veloped. Rather this is a test facility, assembled largely depth; and the display is to be used in a study of terminal from existing machinery and programs, where the systems defense doctrine with an existing simulation program. analyst can work on substantive problems on-I ine with the computer. The essential product of this effort is an under­ standing of the advantages and costs of on-I ine procedures. Background Of course, it is hoped to achieve a useful interim capacity A principal objective of Lincoln Laboratory to develop new to accelerate progress in sel ected areas. computer techn iques is to replace the present awkward pro­ cedures for using computers in the analysis of data and the A block-diagram of the system for this study is shown in Fig­ simulation of systems. At present the analyst is subject to ure 1. During live operation, calculations are made on the detays of a day to a week in obtaining results from a partic­ 7094 in Building J at Lincoln Laboratory and sent by wide­ ular computer run. If he could monitor his program during band I ink to the PDP-1 computer in Building L. The current the run and intervene on-I ine, he would achieve advantages data is shown on the display in the form of a dynamic picture of speed and efficiency. For example, whenever he per­ of RV's and interceptors. The operator makes decisions rel­ ceived the effects of an error of procedure or judgment, he evant to intercept assignments. His orders are sent back to would be abletostop the run, correct the error at once, and the 7094 via typewriter, PDP-1, and data-I ink and cause begin again. During the run, especially with good on-I ine new interceptor launches in subsequent steps. Efficient use displays, he would get an immediate appreciation of the of the 7094 is achieved by dumping the simulation program significance of the results. Often the analyst is testing a onto the disc file and making routine calculations of other hypothesis about the nature of his data or the effect of a sys­ kinds during the relatively long waits between orders from tem parameter. If the results come back while the rationale the analyst at the PDP-l. During the display-development that led tothe hypothesis is still fresh in his mind, his appre­ phase reported here, output of the 7094 simulation program ciation of the results is I ikely to be more rapid and profound. was recorded on tape and run off-I ine at the PDP-l to test For these reasons an on-line facilityshould provide a marked the display techniques. The dotted lines in Figure 1 indicate improvement in efficiency and speed over the present methods the tape links between the cOiilputers. target and the interceptor farms are at the bottom near the I left-hand margin. Reentering objects enter at the upper right, and the nominal trajectory to the target is in the fron­ ~--~- tal plane. The "standard picture," the largest area avai~. I abletothe operator, is about 250 km wide and 120 km hig,~ and depth is perceived readily in the range between 50 km in front of the reentry plane and 50 km behind it. The dis­ play is quantized, and the unit of quantization (which is set by the logical circuitry that drives the CRT) is 1/4 km in WIDEBAND LINK width and height, and 2 km in depth. There is an X2 expanded view. A sel ected volume 125 km wide by 60 km high is expanded by a factor of two in each BUILDING J BUILDING L of the three dimensions--width, height, and depth--and fills the entire display. Off-centering of the expanded area is Figure 1 Block Diagram Experimental On-L ine System provided in the lateral and vertical dimensions, but not in depth. Expansions of X4 and X8 are also provided. Since the unit of quantization is a fixed distance on the face of the The Display CRT, the quantization error in kilometers decreases by a factor of two in all three dimensions with each factor of two The input to the display consists of two kinds of information: in expansion. the locations of objects at successive times and a table of interceptor assignments. The position of each object, RV or The current (or latest) position of each object is represented interceptor, is given in three coordinates of space at 1-second by a point, as in Figure 2. Directly below the point, and intervals beginning at the time of appearance of the first RV. perceived at the same depth, is a number tag representing A table, which is kept up to date second by second, shows the depth of the object in kilometers. (The number "50" is the number of the RV to which each interceptor is assigned. arbitrarily set to represent the depth of the nominal trajec­ The most difficult display requirement is to achieve a com­ tory plane.) Alternatively, the tags may be changed so that plete picture of an engagement--one that presents objects they refer to the numher of the objects in the simulation in three-dimensional space and changes as the engagement program. progresses. Several techniques were considered. For ex­ ample, considerable work has been done recently on the use ., of relative motion as a method for obtaining a perception " " .. ., ,""",,' ".,.", of depth with a computer-driven display. This method con­ 58,," ...... " ...... -:, ...... ... 62'- " ... ...... sists of showing the changing two-dimensional projection RV's 70-;::::::" of a cluster of lines while the cluster is rotating in space. { Previous research at Lincoln Laboratory by Green et al* .. 58} 27 showed that depth is readily perceived during rotation, even ........ 39 INTERCEPTORS . : ••.• 22 if the cluster is made up of a haphazard arrangement of ele­ ..... ments. However, in the case where the elements move with TARGET respect to one another, as do RV's and interceptors in a ter­ minal engagement, the change due to rotation is confounded with change of relative position among the objects. Thus, Figure 2 Analyst's View of Reentry Events an accurate perception of the position of the objects over time seemed out of the question for this appl ication. The dynamics of the engagement are presented by showing *Figure coherence in the kinetic depth effect. J. exp. the analyst 8 seconds of history for each object. The RV Psychol ., 1961, Vol. 62, No.3, 272-282. trails are dashes; the length of the dash is proportional to depth--the longer dashes indicating closer objects. Inter­ ceptor trails are represented by a series of dots. Current The only reasonable way to achieve depth perception ap­ peared to be to use the time-honored principleof the stereo­ position and the number tag are bright and steady, but the scope. A separate view was presented to each eye. Appro­ trailsof interceptor dots and RVdashes are presented in rapid priate geometrical discrepancies were introduced--discrep­ sequence. The timing is such that there are repeated cycles ancies in keeping with the sl ightly disparate views of two of apparent movement along the trail up to the current posi­ eyes viewing objects distributed in depth and viewed at tion. If the analyst wants to review an earl ier portion of the short range--about 30 inches. The two views were painted engagement, i.e. back up in time, he may temporarily des­ on the CRT in an unusual orientation and were seen through ignate any earl ier second as II current time. II He will then. a viewing device. see the positions of the objects at that time, with the usu~ 8 seconds of history behind them. Looking through the viewer, the analyst sees a side view of A maximum of 32 RV's and 32 interceptors may be shown. the engagement, except that his view includes depth. The With that many objects on the display, the analyst needs some way of clarifying the picture.