An Experimental Digital IntBractive Facility'Lawrence A. Gambino and Bryce L. SchrockU.S. Army Engineer Topographic Laboratories

HardwareIntroduction

About 2-1/2 years ago the Army's Engineer TopographicLaboratories and Defense Mapping Agency began develop-ing a digital image processing system for use in map

making. Today that system, if it has not yet supplantedconventional approaches to map'making, has neverthelessdemonstrated the feasibility of digital techniques in photo-interpretation, stereo compilation, and automated car-

tography.Historically, the cartographic and mapping community

has relied upon slow and tedious analog techniques togenerate maps and charts for military applications. Morerecently, hybrid techniques have been employed to decreasethe amount of time required to create the map from photo-graphs and to improve the quality of the final product.Purely digital techniques have been considered, but theircost-effectiveness has yet to be established. Such proof-when it does come-will be the product of a significantresearch program, one that has access to an extensive andpowerful digital image processing system.Meanwhile, the problems facing the researcher in digital

map-making encompass essentially all of the disciplinesof digital image processing: point operations, filtering,geometric operations (rectification, zoom, warp or de-warp,etc.), and pattern recognition. The problems becomeextremely difficult in light of the normal requirement tohandle very large arrays of data, Typically the concern isfor the generation of maps in the scale range of 1:24000to 1:500,000-scale factors that require image resolutionof 2.4 meters to 50 meters, respectively (assuming a pres-

entation resolution of 10 line pairs per millimeter).The usefulness of the final product is largely determined

by the area covered: some maps represent thousands ofsquare kilometers, resulting in the requirement to handlelarge arrays of data. Of course, the problems are consider-ably affected by the need to use three-dimensional imagery(stereo pairs) in the generation of the rmap.Any research facility for exploration of digital techniques

in map generation should place a human in the loop. It isnot surprising, therefore, that our approach to the designof this system-the Digital Image Analysis Laboratory-placed heavy emphasis on interactive processing.

22

Generally speaking, three subsystems make up the Digi-tal Image Analysis Laboratory (see Figure 1): the host con-trol processor (CDC 6400), the associative array processor(Staran), and the image softcopy/hardcopy/digitizing sub-system (Comtal 8300; Dicomed D-56, D-47, D-36; PDP-1 1/50).Each subsystem operates either as a stand-alone ortogether with other subsystems as an entire system where-by digital interactive processing goes on concurrentlywith image processing and testing on the host processor.In the single system mode, imagery can be passed fromone subsystem to another via commands from the Tek-tronix terminals. Processing might take place in Staranon command from these terminals and the results viewedon the softcopy system in a matter of seconds.

Staran. Developed and built by Goodyear AerospaceCorporation, Akron, Ohio, the Staran was delivered to theEngineer Topographic Laboratories in October 1974.Until recently, it was used in a stand-alone mode whichenabled personnel to become familiar with its character-istics and programming structure. All applications imple-mented on Staran have required a considerable rethinkingof the problem in order to take full advantage of itsarchitecture, which is unique among all digital processingsystems.

The major components include four arrays of associativememory (up to 32 are possible), a parallel input/outputunit, a 64-track parallel head disk, printer, card reader,teleprinter, and a PDP-11/20 controller with a disk oper-ating system.Each of the four arrays is composed of 256 words, each

having 256 bits for a total of 1024 words and 262,144 bits.Each array contains 256 simple processing elements.Therefore, 1024 processing elements are available to per-form an operation at the same time. Further, each process-ing element acts on an independent data stream, therebyoffering the theoretical possibility of acting simultaneouslyon 1024 independent data streams. Thus far, I/O restric-tions have kept us from taking full advantage of thisvery large processing bandwidth. However,' we could

COMPUTER

DMA/ETL DIGITAL IMAGE ANAYSIS LABORATORY (DIAL)

I 6633-2EXTENDED CORE SYSTEM 125K

IMAGE DISPLAY SYSTEM IMAGE PROCESSING (STARAN) SYSTEM

Figure 1. The Digital Image Analysis Laboratory. Developmentof the system actually began with the acquisition ofa Staran associative array processor. A search for acentral processor for the control of the Staran result-ed in the acquisition of a CDC 6400 with extendedcore. The combination of the Staran and CDC 6400provided a high level of capability in speed and flexi-bility at a moderate cost. Data display systems were

surveyed, resulting in the selection of a Coomtal 8300.The PDP 11/50 was added to provide the last link in adistributed system and to provide a stand-alone capability to the Comtal display; Other equipment for digi-tizing film data and generating hard copy was In placeand operational at the Engineer Topographic Labora-tories before the new system design was started.

August 1977 23

exploit a- larger portion of this capability by utilizing anexisting high speed port to extended core storage (ECS)on the CDC 6400. To accomplish this a data channel inter-face between extended core storage and the Staran arrayswould have tb be built. That interface would have I/Obandwidths in the 150-300 megabits/second range, whichwould effectively match or exceed processing rates in theStaran. We have already experienced the need for thesehigher bandwidths in our digital image processing opera-tions. For example, many of the simpler routines experiencehigh software and I/O overhead relative to processingrates.A simplified diagram of one array is shown in Figure 2.

The arithmetic operations are bit-serial but word-parallel-architecturally the inverse of conventional computers.

ations can be performed many different ways amongwords of the MDA array. The flip network also allowsa mixed mode operation whereby it is possible to permutea 256-bit word -as a whole, or to divide it into groups(powers of 2) and permute within groups. This capabilitybecomes a valuable asset in data arrangement when theinitial data from a digital acquisition system, suchas NASA's Landsat Multispectral Sensing System, isnot in a format amenable to image processing. Rubenet al.' have provided an excellent description of suchapplications. Detailed information about the entire systemcan readily be found in the literature2 and in the article"Image Processing with the Staran Parallel Computer"by D. L. Rourbacher and J. L. Potter in this issue.

TO/FROM CONTROL

-I

c\j

BITS0.- 255

256 PE'S256 WORDS X 256 BITS PER ARRAY

Figure 2. Associative array.

Another unique feature of the array is its content-addressed (associative) memory. This allows identity of allelements meeting a certain criteria in a single memoryaccess whereas the conventional computer searches itsdata file one element at a time. This feature will findwidespread use in searching an imagery data base forimages which meet certain criteria of interest to a photointerpreter.Uniqueness of the Staran arrays is enhanced even further

by multi-dimensional access and permutation (flip) net-works. MDA allows data to be accessed in both the wordand bit directions; the flip network allows communicationbetween processing elements and with the MDA. TheMDA capability allows shifting and rearrangement ofdata so that parallel arithmetic, logical, and search oper-

CDC 6400 computer. The current configuration of theCDC 6400 consists of four seven-track tapes, one nine-track tape, three 844 disk drives, eight peripheral process-ing units, one bank of extended core storage consistingof 128K 60-bit words and 98K 60-bit words of main corememory. Five additional disk drives are planned, therebyreaching the capacity of one disk controller. The inter-active image processing system utilizes private diskpacks for image analysts and thus places additionaldemands on the number of packs required by the overallsystem.One especially desirable feature of the 6400 series that

makes a significant impact on throughput of the imageprocessing system is the availability of extended coresystem, or ECS. A recently designed high-speed interfacebetween ECS and the arrays of Staran will provide a high-bandwidth data path from ECS through the parallel I/Ounit into the arrays of Staran. The 150-megabit/secondbandwidth provided by this data channel can be increasedto 300 with the addition of another bank of ECS. Thiswould not only represent the first time that Staran's veryhigh bandwidth capability would be tapped; it wouldalso provide the means for alleviating inefficient use ofthe machine's processing power. The potential suggestspossibilities for future digital image processing systems-i.e.,using special processors as off-loaders for host com-puters. This is exactly the way it is currently being usedbut the data channel would provide greater efficiencies.Other components of the CDC 6400 which are being

utilized in somewhat non-standard manner are the periph-eral processing units. These units, which resemble mini-computers with 4096 12-bit words and a repertoire ofabout 65 instructions, control all the peripheral hardwareand much of the operating system software. In the DigitalImage Analysis Laboratory, two of the eight availableperipheral processing units have been essentially dedicatedto non-standard use in that they are used to interfaceStaran and the image processing subsystem to the hostcomputer. These two units are used to accomplish allcontrol and data transfers among the CDC 6400, theStaran, and the PDP-1 1/50-thus relieving the CDC 6400CPU from most housekeeping chores.

Digital image displays. The image display units con-sist of two Comtal 8300-SE systems featuring refreshstorage of three 512 x 512 8-bit images and three 512 x 5121-bit graphic overlays in each system.System software for the Comtal 8300's resides in the

PDP-11/50. This software allows the assignment of bothComtal displays to only one Tektronix terminal or theassignment of one Comtal to each terminal. In conjunctionwith the hardware described below, it also permits efficienttransmission of information between the CDC 6400 andthe Comtal 8300's. For example, it is possible to transmit

COMPUTER

cm:C)

0:

\ BIT SLICE

11s

"I WORD SLICE

_s~~~~~~~~~~%__s~~~~~~~I

_ ~~~~~~~SI_j | | | | 1 |Il

24

any 512 x 512 8-bit image from the CDC 6400 disks tothe Comtal displays in less than 3 seconds.

Channel couplers. Both the PDP-1 1/50 minicomputerand the Staran are interfaced to the CDC 6400 host pro-cessor through identical hardware devices. Each device,or channel coupler, resides on a data channel of the CDC6400 in the same fashion as any other peripheral controllerand thereby requires no data channel converter. They arepassive devices, responding to requests from the periph-eral processing units of the CDC machine. The CDCprocessor acts as the master and the DEC machine asslave, but any transfer operation can be terminated byeither processing unit. It is possible to use this channelcoupler on the Staran/CDC side of the interactive systemsince the Staran is controlled by a PDP-11/20 sequentialcomputer. In this case, the channel coupler is pluggeddirectly into the Unibus of Staran's PDP-1 1/20. As statedearlier, this represents a relatively low-speed channel anddoes not reflect the full potential offered by a special datachannel directly into the parallel I/O of Staran.The channel coupler permits up to four formats to be

programmed. One is a standard data format in which12-bit words from the CDC data channel are transferredto or from the 12 least significant bits of the 16-bit PDP-11words. The three additional formats include two 6-bitbytes from the CDC 6400 to or from the 6 least significantbits contained in the 2 bytes of a PDP-1 1 word, 8 leastsignificant bits of two CDC data channel words into asingle PDP-1 1 word or vice versa, and, finally, transfer ofcore images in either direction. These operations takeplace at approximately a 4.8 megabit/second rate acrossthe channel coupler, but because of software overheadthe effective rates are only about 2.5 megabits/second.This formatting capability allows efficient processing

of digital imagery and has proven very successful inpractice. Detailed information concerning the channelcoupler is available elsewhere.3

PDP-11/50 computer. The PDP-11/50 provides the infer-face between the image displays and the CDC 6400 proces-sor through the channel coupler. As for the Staran sideof the interactive system, the channel coupler is pluggedinto the Unibus of the PDP-1 1/20 and operates in a similarfashion. However, the PDP-11/20 in Staran operates underthe disk operating system, whereas the operating systemin the PDP-1 1/50 is a custom-designed, interrupt-drivensystem and thus operates somewhat more efficiently.In addition to serving as the interface between the CDC

6400 and Comtal displays, the PDP-11/50 is used as thereal-time controller for all devices connected to it. It alsoallows local processing of imagery as opposed to perform-ing all image manipulations on the CDC 6400 computer.Many image processing functions which do not requirethe power of a large scale computer; these are performedon the minicomputer. Such things as grey scale remapping,pseudocolor encoding, and numerous other functions areperformed "locally."Many of these simpler operations can occur concurrently

with processing on the CDC 6400. For example, whilethe PDP-11/50 is remapping the grey shades, the CDC 6400can be pseudocolor-encoding grey shade data stored inthe Comtal display system. This capability providesadded dimension in photo interpretation where rapidlychanging contoured color scenes provide a more vividportrayal of differences in grey shades which relate tosubtle changes in physical and cultural features.Some additional features of importance are related to

the memory of the PDP-1 1/50. We have a total of 32K

16-bit words, half of which consist of a fast MOS memory.All direct memory transfers of data are done in this portionof memory. This enables us to transfer data at a ratealmost commensurate with the full capability of the channelcoupler. Of course, there is a small amount of softwareoverhead which prevents the maximum achievable rate of4.8 megabits/second. However, as stated earlier, we feelthat we have achieved maximum efficiency under thecircumstances in that we can retrieve a 512 x 512, 8-bit/pixel image from the CDC 6400 disk and display thisimage on the Comtal screen in approximately 3 seconds.A 1024 x 1024 8-bit image can similarly be displayed inless than 5 seconds.This is a very general description of a fairly sophisticated

minicomputer. Reliability of both the 11/50 and the channelcoupler has been exceedingly good, and both were opera-tional within a short time after delivery to our installation.

Software

Two of the most interesting elements of the softwareare the Menu system and the Fortran interface. Otherimportant elements control the Staran/CDC 6400 interface,CDC/PDP communication, and the display controllersystem, and the application algorithms. All of these arehighly systems oriented. However, it is via the Menu andFortran interface software that a user communicateswith the system and implements applications of interestto him without having to be a systems analyst. Thesefeatures should speed research in digital image processingsince the data management aspects of handling imageryinteractively will not burden the user in either the imple-mentation of application programs or in the use of theMenu system.

Menu software. This body of software can be referred toas control software since it provides the user a capabilityfor exercising the computer system, processing functions,and hardware peripherals. It is designed to be a tool sinceit is highly user oriented and, as such, it has been tailoredto the needs of the user who has customarily utilized lighttables and microscopes for the extraction of informationfrom photography. In a way, the system will serve as atestbed for using digital image processing techniques asaids in image interpretation. On the other hand, researchfor advancing the state of the art in digital imageprocessing will take place by analysts using the Fortraninterface capability.The basic mode of communication between the user

and the system is through the Tektronix terminal, and itis via this terminal that the non-computer-oriented is ledthrough such image processing operations as search, scale,rotate, translate, generate subimage, reformat, remapgrey levels, etc. A series of multiple image operationsinclude capabilities such as mosaic, color operations, splitscreen, align images, etc. Some of the display operationsinclude display capabilities such as display entire imageor subimage, erase screen, save image, edit images, etc. Auser can access any of these operations via the menu orby typing a mnenonic name corresponding to the opera-tion such as "ROT" for the rotation operation. Beforethese operations are performed, the function dialoguerequests the user to enter the image name, Comtal displayname, and other relevant parameters.Generally speaking, many application programs exist

within the Menu system. For example, there are threerotation operations consisting of a fixed rotation, a speci-fied angle rotation, and a rotation specified under cursor

August 1977 25

control. The first option allows the user to execute fixedcardinal angle rotation with no further prompting. Option 2requires the user to enter more information about theoperation, and Option 3 requires interaction on the part ofthe user to access flexible rotation routines requiringfurther input.

Many image operations are available to the user whois not computer oriented. To date, we have approximately80 different operations in the Menu system, many of themhaving more than one level of prompting. This tool isdesigned to assist a photo interpreter in making decisionsquickly and accurately and should also prove valuable toimage analysts who wish to pursue research in digitalimage processing.

Fortran interface software. The control software allowsthe user to access his own Fortran programs using sys-tem routines for input/output and to execute them fromthe Tektronix terminal. This body of software also allowscommunication with the Staran via Fortran-callableroutines. For example, there are 11 routines available tothe Fortran program which, in general, are designed todetermine the status of both the CDC 6400 and Staranand to transfer control information and data between thetwo machines.The Staran portion of the Fortran interface software

allows both batch and interactive Fortran programs tobe implemented on the system. One of the 11 routinesallows this decision to be made by the application pro-grammer. For example, the Fortran-like statement CALLQUEUE (BQU, IQU) returns the number of jobs in thebatch queue (BQU) and the number of jobs in the inter-active queue (IQU). This helps an interactive job decidewhether it wants to use Staran or wants to do its com-putation on the 6400 only.Other Staran/6400 related routines perform such tasks

as providing the status of Staran, placement of the routinein one of two queues, initiation of loading and executionin Staran, transmission of control information from the6400 to Staran and receipt of control information fromStaran, transfer of buffered data from 6400 to Staranand vice versa, transfer of various status indicators forread/write operations, initiation of Staran debug modules,and, finally, detaching Staran from the system.That body of software which allows the Fortran pro-

grammer to easily task the other components of the systemis called the Fortran Interface Routines To The InteractiveImage Processing System." It enables him to use theTektronix and Comtal displays via Fortran-like statements.The imagery data transfers and manipulations are accom-plished through 9 Fortran statements such as reading andwriting with their associated arguments describing thearray, word count, file name, and a recall flag whichindicates whether control returns to the CALLING pro-gram module before or after the WRITE operation iscomplete. Other statements relate to such things as pack-ing and unpacking fixed and floating point words. Forexample, a call to the routine UNPKI with associatedarguments converts packed data to 60-bit integers.Tektronix-related Fortran calls include such things assending characters to the Tektronix terminal, readingdata which has been typed in at the terminal, drawinglines and plotting points on the Tektronix screen, etc. Thelist for the Comtal Fortran calls is even longer. Mentionwill be made here only of the CALL CURSXY routinewhich sends and receives Comtal cursor coordinates. Thisis a very important capability to have for our applicationsin digital stereo-photogrammetry and other activitiesrequiring mensuration of digitized aerial photographs.

26

Applications

The applications being researched for the Defense Map-ping Agency fall into four functional areas: (1) digitalstereo-photogrammetry, (2) automated cartography, (3) digi-tal image processing, and (4) storage and retrieval. Theseareas were chosen based on the capabilities of Staranrather than on the capabilities afforded by a total inter-active system, which was in the early stages of developmentat the time. We will touch upon only two of these fourareas with a bit more emphasis on image processing.

Digital image processing. Digital image processing forthe Defense Mapping Agency aims at cost-effective, accu-rate extraction of features from aerial photographs. Thesefeatures, cultural and physical, go into a data bank forlater use in the generation of various topographic product-.In working towards a feature extraction operation, the

digitized photo must be processed to a reduced form leav-ing only the information of interest. In an excellent refer-ence on the subject, Holdermann et al.4 state that thereis no unique classification scheme for particular featuresand feature extraction methods because there are severalroutes to approximate the same results.Several algorithms related to feature extraction have

been implemented on the interactive system using allmajor components. Holdermann et al. consider thesealgorithms as pixel-oriented as opposed to region- andimage-oriented. Dr. Friedrich Rocker of the ResearchInstitute for Information Processing and Pattern Recog-nition implemented these algorithms on the interactivesystem and derived execution times and software overheadinformation. These same algorithms were implemented ona batch-oriented CDC 3300 computer at his institute.The first and most primitive of these pixel-oriented

algorithms to be discussed is the two-dimensional differ-entiation of an image. Several window sizes were movedthroughout images of sizes 256 x 256, 512 x 512, and1024 x 1024 pixels, 8 bits per pixel. Total processing timeand Staran compute times were derived along with soft-ware overhead calculations and time spent waiting forinput/output. The latter figures are presented in percentof total processing time. For example, the differentiationalgorithm consumed a total of 0.8 seconds of which0.1 seconds is Staran compute time for the 256 x 256 imageusing a 3 x 3 window. This represents only 8% of the totaltime while 35% of the time was spent in software overheadand 57% in waiting for I/O. The total processing timeincludes retrieving the image from the CDC 844 disk. Thedata is passed to central memory, to a peripheral process-ing unit, to Staran bulk core, to Staran arrays, and backthrough the same route to be stored on the CDC disk. Ona dedicated CDC 3300 computer, the compute time was16 seconds approximately 160 times slower than Staran.Using a 15 x 15 window this same algorithm consumed atotal processing time of 1.1 seconds for the 256 x 256image, 2.3 seconds for a 512 x 512 image, and 10.9 secondsfor the 1024 x 1024 image.Two other parameters are derived from this analysis: a

processing bit rate and a transfer bit rate. The latter par-ameter is generally twice the processing rate. Looking atthe 512 x 512 with the 15 x 15 window scenario citedabove, we achieved a processing bit rate of approximately898K bits/second and a transfer rate of approximately1.8 megabits/second.Another algorithm implemented on the system is called

a mask comparison. This process yields directional infor-mation about edges occurring in the image. Masks ofdifferent orientations are compared to a small section ofthe image grey levels, and the direction of the mask with

COMPUTER

the best fit will be the local direction of an existing edge,if any. Masks were implemented using several windowsizes. Eight different orientations were used for eachmove of the window throughout the image. Total pro-cessing time for the 256 x 256 image was approximately11 seconds using the 7 x 7 window, and Staran computetime was approximately 10 seconds. Therefore, about4 percent of the time was in I/O wait and 5 percent insoftware overhead with 91 percent in Staran computing.This reflects a completely inverse situation when com-pared to our first example; that is, I/O wait and softwareoverhead are minimal while Staran compute time domin-ates the total processing time.Another algorithm which yields similar statistics as the

mask comparison, and is also used to generate local direc-tions, is known as the plane approximation method. Thistechnique is applied directly to a grey-level picture whichis regarded as a three-dimensional distribution. Smallplanes of fixed size are oriented so that the volume formedby the plane and the local grey-level distributions is aminimum. The resulting normal vector yields informationabout the slope and direction of edges in the images.

Several window sizes were used in the plane approxima-tion method. For the 7 x 7 window case, the total process-ing time for the 256 x 256 image was approximately 8 sec-onds with Staran compute time being approximately7 seconds. If a dedicated CDC 3300 is used for this oper-ation, there is about a 45 to 1 increase in speed. I/O waitaccounts for about 6 percent of the total processing time;software overhead amounts to about 7 percent, and Starancompute time accounts for the remaining 87 percent.Here we have a statistical situation similar to the mask

comparison, but the algorithm is faster and yields thesame kind of information-namely, directional informationrelated to edges in the image. This was the reason the lateDr. Fritz Holdermann4 investigated this procedure. Inboth the mask comparison and plane approximation, theStaran is kept busy computing-a more desirable situationthan that related to the differentiation process wheremost of the total processing time is spent in I/O wait andsoftware overhead.

Convolution using 3 x 3, 5 x 5, and 15 x 15 windows was

also implemented on the system. For the smaller windowsand images, the statistics are similar to the differentiationprocess-that is, high I/O wait and software overhead andlow Staran compute times. For the 256, 512, and 1024images, the total compute times were 4, 9, and 21 seconds,respectively, using the 15 x 15 window for each case.

A 1024 x 1024 image was recently processed throughthe mask and plane approximation routines. Total process-

ing time was approximately 133 and 79 seconds, respec-

tively, using 13 x 13 windows in each case. We see thatthe difference in compute time between the two algorithmsbecomes even more pronounced with larger images andlarger windows. We can only guess how much time itwould have taken on the dedicated CDC 3300. Estimatesrun from several days to at least a week.These statistics underscore the desirability of the high-

speed interface mentioned earlier. This kind of hardwarewill generally minimize the high percentage of I/O waitfor many applications and will create the more favorablesituation of higher compute percentages. It will be interest-ing to note over the next several years how photo inter-preters will react to the interactive system and whetherthey will benefit more from the simple but I/O-boundalgorithms as opposed to the more complex, compute-bound situations. Nevertheless, hardware improvementsshould be made in both I/O and computer architecture inorder to facilitate research in digital image processing.

Reader Service Number 6

The first examinations for the Certificate in Computer Pro-gramming (CCP) will be held on October 22, 1977,at selectedcollege and university test centers throughout the world.

Specific requirements for this year's three separate examina-tions in Business, Scientific, or Systems Programming aredetailed in the "Certificate in Computer Programming Exami-nation Announcement and Study Guide." The study guideand application form for the 1977 examination are availableon request from ICCP.

Please forward the "Certificate in Computer ProgrammingExamination Announcement and Study Guide" along withapplication and test site list.

Name

Street Address

City State or Province Zip Code

Reader Service Number 7

SAVE 5% To 15% On TheWorld's Finest

Hardware & Software.Call (315) 637-6208 NOW.

List Price Our PriceIMSAI 808 Kit with 22 slots $751 $645IMSAI 4K 5OOns RAM Kit $139 $117North Star Micro-DiscoSystem Kit $699 $599

Gromemco Bytesaver Kit $195 $185Vector Graphic 8K 5OOns RAM(Assembled) $265 $225

Edge Connectors & Guides for IMSAI(In lots of 10-each) $ 7 $ 4

Our own Extender Boardw/connector $ 30 $ 15

Shipping charges: $10 per CPU or larger units; $1.50 per kit.$2.00 minimum per order.

Provided stock is available, we will ship immediately for pay-ment by cashier's check, money order or charge cards. Allow3 weeks for personal checks to clear.N.Y. State residents add appropriate sales tax. Prices maychange without notice.

PO.ox71 Fae teville,NewY TM

P.O. Box 71 * Fayetteville, New York 13066m-

I

Digital stereo-photogrammetry. The process of makingmaps usually begins with mensurating aerial photographsto reconstruct the geometry at the instant of exposure inthe aerial camera and continues with the process of extract-ing elevation data from stereopairs of these photographs.The interactive system will be used to investigate both ofthese processes for the Defense Mapping Agency.The removal of parallax and the extraction of elevation

data from stereo images, called the stereocompilationphase of the map-making process, involves correlating thestereo imagery. In this phase conventional, sequentialcomputers using digital correlation techniques cannotcompete with the electronic devices used in the DefenseMapping Agency's production centers. Parallel digitalprocessors must be developed if digital techniques are tocompete with existing production systems.We have implemented correlation algorithms on Staran

and on CDC's so-called "Flexible Processor." Both showpromise in being able to do the stereocompilation speedily,cost-effectively, and accurately. For example, we havedemonstrated that Staran can correlate imagery from asmall section of a stereo image in a matter of seconds.Since we have not digitized a whole stereo area of 9-inch x9-inch photographs, we extrapolated our compute timesfor the entire area and arrived at a few minutes of Starancompute times, to which we added round-trip travel timesfrom disk. This brings us into the 10- to 20-minute range,depending upon pixel size and spacing for the stereocom-pilation of a 40-square-inch area of overlapping photo-graphs. This is an ideal situation in that no considerationis given to additional software strategies required whenencountering areas of difficult correlation, such as waterbodies. This problem exists no matter what technology isused for correlation-digital, electronics, or optical.We intend to use the interactive system for various

phases of the map-making process. In the photogram-metric phase, we will use the Comtal displays for passpoint mensuration-i.e., the phase of the process whichreconstructs the geometry of stereo photographs-andthen proceed to extract three-dimensional information onan ad hoc basis. This does not imply that the interactivesystem represents production equipment. It will takemany years before a production-oriented digital mappingsystem that is flexible and efficient enough can replacethe numerous, non-standardized pieces of special purposeequipment in the Defense Mapping Agency's productioncenters. This will be evolutionary and will be preceded byspecial-purpose digital processors dedicated to the individ-ual tasks such as rectification, mensuration, stereocom-pilation, etc.

Conclusion

Our experience thus far with the interactive system hasbeen very favorable. For example, two-dimensional, inter-active warping now takes only 17 seconds for a 5122 image,whereas it took a week, or longer, to perform in a batchenvironment. The reason for the great reduction in timeis that the latter situation required tedious manual count-ing of pixel positions from portions of corresponding imagewhich were output on a line printer. It required severalruns on the computer to be assured that the manual deter-mination of corresponding image coordinates was adequate.On the other hand, the interactive system, which includesa cursor coordinate capability with the high resolutiondisplay, provides a rapid solution to the same problem.Nevertheless, until we can show that digital processes

are cost-effective, fast, and accurate, they will remain idlecuriosities in the eyes of production personnel. The current

crop of map-making instruments will remain the dominantmeans of accomplishing the task, and the ordinary lighttable will remain the photo interpreter's primary tool.Convincing them otherwise will require a lot of R&D inboth hardware and software.We are in the process of integrating an advanced display

system into our facility so that some of the processesdescribed earlier will be almost instantaneous. This develop-ment will represent a significant achievement in digitalimage processing, and it should also be appealing fromthe photo interpreter's point-of-view. Any further discus-sion of this development must necessarily be left forfuture articles. U

References

1. Sherwin Ruben, Rudolf Faiss, John Lyons, and MatthewQuinn, "Applications of a Parallel Processing Computerin LACIE," 23 August 1976. Presented at the 1976 Inter-national Conference on Parallel Processing, Waldenwoods,Michigan, August 24-27,1976.

2. Lawrence A. Gambino and Roger L. Boulis, "StaranComplex, Defense Mapping Agency-U.S. Army EngineerTopographic Laboratories," 1975 Sagamore ComputerConference on Parallel Processing, pp. 132-141.

3. Robert Edwards, Robert Eggert, and John Martin, "OptionDescription, DRHCD, CDC Channel Coupler," ComputerSpecial Systems, DEC, California, September 19,1974.

4. F. Holdermann, M. Bohner, B. Bargel, and H. Kazmierczak,"Review of Image Processing," Research Institute forInformation Processing and Pattern Recognition, Karlsruhe,Germany, July 1976.

Lawrence A. Gambino is director of the Com-puter Sciences Laboratory at the U.S. Army'sEngineer Topographic Laboratories, FortBelvoir, Virginia, where he is responsible forseveral large-scale, digital image processingprograms under the sponsorship of the DefenseMapping Agency and the U.S. Army Corp ofEngineers. He is actively engaged in explor-atory and advanced research involving the

_______ application of digital image processing todigital mapping for the mapping and charting community. Thisincludes special emphasis on digital architecture and on massstorage systems for the efficient handling of digital imagery. Heis a graduate of Syracuse University and was a mathematicianwith long experience in scientific, electronic computations inboth industry and government before coming to USAETL.

Bryce L. Schrock is a physical scientist atthe U.S. Army's Engineer Topographic Lab-oratories where he is responsible for thedesign and implementation of a large-scaleinteractive digital image processing system.He has been a research associate at UCLA,a research scientist at Battelle MemorialInstitute, a senior member of the technicalstaff at Computer Sciences Corporation, anda consultant for the Rand Corporation. At

CSC he was responsible for the implementation of a batch digitalimage processing system.Schrock received his BS from Purdue University and his MS

and PhD in experimental high energy physics from UCLA atLos Angeles.

COM PUTER28