US3571932A

US3571932A - Digital planimeter

Info

Publication number: US3571932A
Application number: US673577A
Authority: US
Inventors: John G Peddie
Original assignee: H Dell Foster Co
Current assignee: H Dell Foster Co
Priority date: 1967-10-09
Filing date: 1967-10-09
Publication date: 1971-03-23
Anticipated expiration: 1988-03-23

Abstract

This invention relates to a planimetry and particularly to planimetric apparatus whereby digital representations of the cursor movement in one of two orthogonal reference coordinates are provided in incremental fashion to register means for accumulation and temporary storage. The movement of the cursor in the other of the orthogonal reference coordinates causes the information in the register to be transferred to a down counter. The down counter is pulsed, by means of clock pulse signals, to a zero condition. Simultaneously the clock pulses are provided to an adder subtracter device which accumulates the pulses until the down counter obtains the zero output condition. Control means are provided such that the pulse information which is entered into the adder/subtracter unit provides the correct updated pulse accumulation which represents the total summation of the incremental information stored in the register and periodically transferred to the down counter. The accumulated information in the adder/subtracter device may be displayed to provide a current indication of the area traversed by the cursor.

Description

United States Patent lnventor Appl. No. Filed Patented Assignee John G. Peddie San Antonio, Tex. 673,5177 Oct. 9, 1967 Mar. 23, 1971 H. 11 Foster Co. San tonio, Tex.

DIGITAL PLANIMETER ll glaims, 1 1 Drawingfigs. ugsg ci,

33/123, 235/92 G0lb 7/32, G06g 7/18 3 /123.

References Cited UNITED STATES PATENTS l 1/1956 Roth 7/1960. McAuslan et a1. 7/1961 Walkeretal. 2/1967 Woodard et a1.

Primary Examiner-Robert B. Hull Attorney-Watson, Cole, Grindle & Watson ABSTRACT: This invention relates to a planimetry and particularly to planimetric apparatus whereby digital representations of the cursor movement in one of two orthogonal reference coordinates are provided in incremental fashion to register means'for accumulation and temporary storage. The movement of the cursor in the other of the orthogonal reference coordinates causes the information in the register to be transferred to a down counter. The down counter is pulsed, by means of clock pulse signals, to a zero condition. Simultaneously the clock pulses ar provided to an adder subtracter device which accumulates t e pulses until the down counter obtains the zero output condition. Control means are provided such that the pulse information which is entered into the adder/subtracter unit provides the correct updated pulse accumulation which represents the total summation of the incremental information stored in the register and periodically transferred to the down counter. The accumulated information in the adder/subtracter device may be displayed to provide a current indication of the area traversed by the cursor.

DIGITAL PLANIMETER The measurement of both regular and irregularly-shaped areas on plane surfaces has long been accomplished using mechanical planimeters such as those originated by Kelvin, Amsler and others and later developed to a high degree of precision and usefulness. Such mechanical integrating instruments are in common use in many civil and mechanical engineering applications. Although these mechanical planimeters are employed frequently 'in photogrammatic analysis, deliberate and painstaking operation is required to insure even modest accuracy.

Modern photogrammetric processing generally utilizes very rapid scanning and interpretive procedures so that any manual steps within the overall process represent serious time delays. It is desirable that the speed of such slow steps in the determination of areas be increased to be more consistent with automated processing procedures. In addition, it is preferable that the accuracy and reliability of measurements be improved over that obtainable with purely mechanicalarrangements. Finally, it would be advantageous to generate information in the form of electrical signals which could be displayed either directly or stored for later use in a computational procedure for determining area measurements.

In well-known graphical techniques, an area to be measured may be divided into parallel strips of unit width and the total area obtained as the product of the unit width and the sum of the lengths of the strips. Various mechanical arrangements have been devised to utilize this apparently simple process, but such arrangements are limited in accuracy by the difficulty of making the strips sufficiently narrow. By use of optical and electronic techniques, however, the measuring increments or strips" may be made quite small because the fonnation of the strips is limited only by the resolving capability of lens systems, photographic media and scanning patterns. Similar improvements can be effected, of 'course, in determining the lengths of the incremental strips and in the summation of the increments to obtain their total value.

For most measurements utilizing rectangular integration methods, the area under a given curve is found merelyby the summation of the coordinate values represented by the curve in the coordinate system. In the usual planimetric problem on a map, however, the area of interest is bounded by a closed curve spaced away from the reference axes. Accordingly, the measuring arrangement must utilize the full coordinate values while at the same time providing for the subtraction of the incremental areas which lie outside the boundary curve.

Briefly, in the present invention the boundary enclosing the specified area is traversed by a cursor element which actuates coordinate encoders for the generation of electrical signals representing incremental movements of the cursor element as it is caused to traverse the boundary. The electrical signals are provided to reversible digital counting apparatus, of a unique design, and timing and control means are provided to control the reversible counting apparatus such that the incremental areas are algebraically mounted to' obtain the total area traversed by the cursor. The total area may then be displayed. The area to be measured need not be'immediately adjacent or in any specific predetermined relationship to the reference axes.

Accordingly, the primary object of this invention is to pro vide apparatus capable of rapidly and accurately measuring area on graphic media such as maps, photographs and drawings. 'Another object is toprovide apparatus for measuring areas which need not be in adjacent or predetermined relationship to the coordinate reference axes. Still another object is to provide a digital planimeter in which the measured area is indicated immediately in digital format. Yet another object of the invention is to provide a digital planimetric apparatus which can be assembled readily from standard logic elements which are commonly used in data processing equipment. Finally, it is an object of the invention to furnish a planimetric apparatus which is fully compatible and integrable with digital computer processes and apparatus.

These and other objects and novel features of the invention will become apparent in the following description and the related accompanying drawing wherein:

FIG. I is a schematic showing the principal elements of the scanning portion of the digital planimeter and their interrelationship;

FIG. 2 is a graphical illustration showing an area to be meas'ured placed upon a system of reference coordinates;

FIG. 3 is a simplified block diagram of one arrangement of logic apparatus required to carry out the invention;

FIG. 4 is a block diagram illustrating one preferred arrange ment of the digital logic elements required for implementing the invention of FIG. 3;

FIG. 4a represents the implementation of the logic circuitry for performing the carry function;

FIG. 4b illustrates the detailed implementation of the quadrature converter circuitry;

FIG. 40 shows typical signal waveforms in the quadrature converter circuit;

FIG. M is a block diagram of the timing network for the digital planimeter;

FIG. 4e illustrates typical waveforms at the various points indicated in the timing network shown in FIG. 4d;

FIG. 5 is a block diagram representation of the circuitry for controlling the adder/subtractor' elements of the invention; and

FIG. 5a is a detailed block diagram of the up-down control circuit illustrated in FIG. 5. 7

Referring to FIG. 1 of the drawing, scanning frame [0 is arranged to hold in fixed relationship the map, photograph or drawing 12 containing an area 13 which is to be measured. A movable cursor assembly 14, with reticule I5, is arranged to slide smoothly along horizontal arm 16 and thus transmit its horizontal motion to the X-encoder 20 by means of cable 17 and pulleys 18, -19. Horizontal arm 16 is also arranged so as to slide smoothly in the vertical direction along guides 23, 24 and to simultaneously actuate Y-encoder 25 by means of cable 28 and

pulleys

29, 30. A similar cable 250 and associated pulleys 26, 27 are provided adjacent to guide 23 to provide a balanced and smooth operatingmotion.

In measuring area 13 the operator manually moves cursor assembly I4 carefully along the boundary line as observed in reticule 15. The motions of cursor 14 are transmitted to X-encoder 20 and Y-encoder 25 which generate displacement signals which are utilized in the data recording or area computation circuitry to be described in detail hereinafter.

'Referring to the graphical representation of FIG. 2, area [3 may be considered as defined by the boundary 1 and y coordinates referenced to the zero origin. Thus, if the planimeter index or cursor 14 is placed on the boundary curve at, say, any Y-line, the x-coordinate value may be determined. As cursor l4 traverses the boundary curve it may be assumed that a halt is made at each Y-line, representing an incremental command step, and that the associated x-coordinate value is determined during the halt. In effect, the x-coordinate readings taken at the two boundary intercept points xl and x, will furnish the incremental distance (x x which when multiplied by the y-increment step, or Ay, will furnish the small incremental area, y (XV-2) I Since the y-increments or command steps are all equal, it can be seen that the order in which x-coordinate values are determined is immaterial in the final summation, provided the boundary curve is traversed carefully and without overlap.

Further, it is also evident that the absolute values of x,,x2...x,, can be used in a defining algorithm if some means is provided for determining when the cursor is moving away from or toward the x-axis. Thus, if y is chosen as the command coordinate, which is to determine the measuring increment, then the x-coordinate value can be defined as positive when y is moving away from the x-axis, and negative when y moves toward the x-axis. More simply, x can be considered positive when the y command value, as defined by the usual x-y coor dinate system, is increasing, and x must then be recorded as negative when the y command is decreasing in value.

Using-these definitions, an algorithm may be written to show the necessary operational relationship:

h =Ay=increment of y; the command coordinate Thus, when all values of the y-command coordinate have been traversed and the related x-coordinate values recorded, the total area may be computed by substitution in the algorithm. The proper sign for each x-coordinate value may be determined readily by noting the direction in which y-command has changed since the last halt. The total area is then determined by algebraically summing all the values of the x-coordinate and multiplying this sum by the incremental value of y.

The above-outlined calculations may be automatically computed by the arrangement of apparatus shown in FIG. 3, X- converter 21 is actuated by horizontal movements of cursor 14, shown in FIG. 1, to furnish electrical output signals in digital form to up-down counter 34 comprising sufficient binary (or binary coded) register to permit the desired range of measurement. Various means, which will be described later, may be arranged to supply up-down signals corresponding to increasing or decreasing values of the x-coordinate. The output from up-down counter 34 is transferred to adder/subtractor 35 upon receiving the transfer command from y-converter 22. Whenever cursor 14 moves one increment in the y direction, the adder/subtractor 35 is actuated and acquires the date then accumulated in up-down counter 34 and transfers this data to accumulator 36, where the transferred data is algebraically summed. The total accumulated value may be shown on display 37. This indicated x summation multiplied by the value of the y increment represents the measurement of the desired area.

The simplified representation of FIG. 3 is shown in more detail in FIG. 4 which shows one preferred logic circuit for carrying out the invention. X-encoder and quadrature converter 38 furnish coordinate pulses and sign control signals to the X to register 70 which includes

stages

71, 72, 73, 74. Stages 7174 are interconnected respectively by carry logic circuits 7577 such that X-register 70 operates as an updown counter in response to the input signals provided by quadrature converter 38. Binary-coded-decimal format is preferred for compatibility with associated equipment and analysis. Suitable up-down signals, actually representing the sense of either forward or reverse rotation of X-encoder 20, are derived by phase comparison means in quadrature converter 38. Such rotation-direction indicating techniques are well known in the instrumentation art and described in detail in references such as Control Engineer's Handbook, John G. Truxal, Editor, 1958, McGraw-Hill Book Co., New York.

Although various types of up-down counters may be adapted for use in X-register 70, the novel three-input counter disclosed in my previous US. application Ser. No. 657,936, filed Aug. 2, 1967, which became US. Pat. No. 3,544,773 is especially suitable and preferred. The use of four

stages

71, 72, 73 and 74 in X-register 70 is, of course, by way of illustration and additional units may be included to extend the range and accuracy.

Up-down counter stages 7174 comprising x-register 70 provide. means for accumulating instantaneous incremental values of the x-coordinate. In order to automatically compute the area, it is necessary that the instantaneous incremental xcoordinate values be transferred or read out at the sampling or y-increment instants, as determined by the output from Y-encoder 25. Using the previously described graphical illustration, this Y-encoder transfer signal or command occurs at the instant corresponding to the crossing of a Y-line on the graph.

Down counter 80 the operation of which is more fully described below, comprising stages 8l84, is actuated from timing network 120 in response to a command signal from Y- encoder and quadrature converter 86, so as to acquire by transfer the x-coordinate values from X-register 70 at the proper sampling instants. The x-coordinate values must, in turn, be given the proper sign and transferred permanently to accumulator 88 so as to accumulate an updated summation of the x-coordinate values which is shown l'rnally on display 37. This transfer of information is effectively provided to accumulator 88 by utilizing controlled clock signals, from clock I30, to pulse down counter down from the stored xcoordinate value to a zero count, which condition is recognized by zero recognition NAND gate 85. The output of NAND gate disables the clock signal by turning off clock control gate I25.

Simultaneously with the down counting of down counter 80,

clock pulses are transmitted to accumulator 88 to effect the algebraic summation with the previously accumulated x count. Accumulator 88 comprises another group of counter stages 8993 which may be interconnected as shown in my previously mentioned US. Pat. application Ser. No. 657,936.

The operation of the apparatus in FIG. 4 may be understood more clearly by the following step-by-step outline:

l. The current x-coordinate pulses from X-encoder 20 are converted into digital form by quadrature converter 38 and temporarily stored in X-register 70.

2. When the y increment or command signal is generated by Y-encoder 25 (y has crossed a line"), timing network is actuated so as to disable, via clock control NAND gate 125, pulses from clock I30. Simultaneously, the timing network 120 furnishes a transfer command to down counter 80 to accept the count reading from X-register 70.

3. When the X-register count is present in down counter 80, clock I30 starts sending pulses into down counter 80 via clock control gate under control of timing network 120. Simultaneously, clock pulses are sent into accumulator 88 for addition or subtraction as controlled by the up or down" signal from the y quadrature converter 86 and accumulate with the previous count retained therein.

4. The zero output condition of down counter 80 is sensed by zero recognition NAND gate85 which then stops the clock pulses from clock I30 by disabling clock control gate 125.

5. The clock pulses into accumulator 88 are terminated and the accumulated total count is shown on display 37 as the x-coordinate summation. The accumulated and updated total in accumulator 88 which is displayed by display 37 is the current total area traversed by cursor l4 since the y incremental constant is conveniently selected as unity.

With respect to functioning of down counter 80, it should be noted that the counter stages 8l84 are held permanently in a down mode by a logical I applied to the down input, while the up input is permanently connected to logical 0 as represented by the circuit ground. This control configuration is necessitated by the fact that down counter 80 is preferably constructed in accordance with the Reversible Binary Coded Decimal Synchronous Counter Circuits" as described in my aforementioned pending US. Pat. application Ser. No. 657,936. Those skilled in the art will recognize that more conventional down counter circuits can be substituted for that shown in FIG. 4 to accomplish the function of that apparatus.

Carry logic circuit 75 comprises inverter 78 and NAND gate 79 as shown in FIG. 4a. The pulse signals from X quadra ture converter 38 (FIG. 4) are inverted and logically combined with the carry output signal C,, from counter stage 7]. The output of NAND gate 79 is then applied to the input of carry logic circuit 76 along with the carry output from counter stage 71. Carry logic circuits 76 and 77 are similar to carry logic circuit 75 with the exception that for carry logic circuits 76 and 77 the input shown in FIG. 4a is replaced by the carry output signal from carry logic circuits 75 and 76, respectively.

An embodiment of the circuitry comprising X quadrature converter 38 is shown in FIG. 4b. The operation of the converter will be more easily understood with reference to the signal waveform shown in FIG 4c. Quadrature converter 38 is comprised entirely of NAND gate circuit elements, inverter circuits using a NAND gate circuit configuration, and capacitor-resistor networks which serve to provide the necessary differentiated pulses. The NAND circuit configuration is for convenience only, since most of the logic elements of the digital planimeter are comprised of such NAND gate elements. Those skilled in the art will recognize that other logic circuitry may also be substituted for that shown in FIG. 4b to perform 5 the necessary functions of the quadrature converter circuitry. The two series of output signals from Xencoder are out of phase by 90 as indicated by signal waveforms A and B in FIG. 40. Output signals A and B are provided to

inverter gates

39 and 47, respectively, (which are NAND gate elements having their inputs paralleled to perfonn an inverter function). The inverted outputs A and B are respectively applied to capacitor-

resistor netwgks

41, 42 and 52, 53 to form the indicated output A and B". These signals are respectively inverted by

inverter circuits

43 and 54 to provide signals A" and B" which are shown in FIG. 4c in relation to encoder output signals A and B. Simultaneously, the respective outputs from

inverter circuits

39, 47 are provided through

inverter circuits

40, 48 respectively, and then to capacitor-resistor networks 0 44, and 49, 50, respectively,- to provide the indicated outputs A and B. The signals A and B are then each inverted, respectively, by

inverte circuits

46 and 51 to form the indicated outputs A: a r id B which are also shown in FIG. 4 The signals A", A, B and B", along with the signals A and B are provided to NAND gate circuits 5562 in the indicated manner so as to be combined to provide the logic signals appearing at the output of NAND gate circuits 5562. These outputs are then combined accordingto the logic equations at the bottom of FIG. 4c in NAND gate elements 63 and 64 to form the necessary UP, DOWN control signals for register 70 which is shown in FIG. 4. The pulse output from the X-con verter, which is indicative of the movement of the cursor in the X-direction, is formed through NAND gate 65 and inverter 66 in accordance with the logical equation appearing at the bottom of FIG. 4c. The UP, DOWN and pulse output signals of the X-converter provide the necessary control signals to properly operate register 70 so as to provide therein an instantaneous accumulation of information which represents the movement of cursor 14 in the X-direction.

The Y-encoder circuitry is similar to that of the X-encoder circuitry just described except that the pulse output signal from the Y-converter is altered such that each pulse output represents a traversal of one unit of the cursor in the y coordinate direction. Thus, the Y quadrature converter circuitry 45 130 may preferably comprise an oscillator having a sufficiently high oscillation frequency to provide the necessary accuracy of measurement. For example, the oscillator frequency 5 of clock 130 may be five megacycles. The oscillator is synchronized with the output pulse from quadrature converter 86 to form the clock pulses which are provided toNOR 122 along with the pulse output from Y quadrature converter 86. As shownin FIG. 4e the clock pulses B at the output of NOR 122 are controlled by pulses A, and provided to clock control gate 125 through inverter 140. The NORd pulses are also provided to the clock inputs of flip-flops 123 and 124. Flip-flops I23 and 124 are interconnected to provide the indicated signal at D which serves to control the gating of inverted clock pulses B, in conjunction with zero detection signal E which is obtained from zero recognition circuit from the zero output condition of counter stages 81-84 in down counter 80. The inverted I3 clock pulses, along with signal D and zero detection signal E, are provided to the input of NAND gate 126 and the output of NAND gate 126 is inverted by inverter 127 to provide the indicated control clock output signal G. This latter signal is applied, as shown in FIG. 4, to the clock inputs of the respective counter stages of down counter 80 and also to the respective counter stages of accumulator 88 only when zero detection signal E is at an up level as shown in FIG. 40. The transfer command signal to down counter 80 is formed by providing the indicated signals from flip-flop I23 and I24 to NAND gate 138. The output of NAND gate 128 is inverted by inverter 129 to form the transfer command signal indicated as signal F. Transfer command signal F- indicates the transfer of the accumulated information from register 70 into down counter 80 as described previously.

Although the arrangement described in FIG. 4 is quite reliable and capable of high accuracy when properly instrumented, it is subject to certain operational limitations. For example, to prevent gross errors the operator must take care to move the cursor always in the same direction. clockwise or counterclockwise about the area to be measured when starting a measurement. In addition, the described arrangement requires that the area to be measured extend only in a single quadrant with reference to the origin of the coordinate system. Accordingly, an alternate arrangement is preferred in which all measurements are made essentially automatically and may extend to all four quadrants.

Referring to FIG. 5 of the drawing,'up-down control I02 has been added to the previous arrangement to provide quadrant recognition and suitable output control of accumulator 88. Up-down control 102 is actuated by input signals from X-encoder 20 (via quadrature converter 38) and Y-encoder 25 (via quadrature converter 86).

The logical design of up-down control 102 is based on three requirements: (I) the sign of X, from the X-encoder 38, must be known; (2) the sign of Y, from the Y-encoder 25, must be known; and (3) the zero or nonzero condition of up-down counter stages 8 993, considered together, must be recog nized. Next, it is assumed that the origin (X=0.Y='O) of the coordinate system is located at some point on the boundary of the area to be measured and all up-down counter stages set to zero, after which cursor 14 (FIG. 1) is moved in either direction along the boundary of the area until a Y increment is crossed as indicated by Y-encoder 25.

Assuming that 2 refers to the zero condition of the updown counter stages 8993, that ADD refers to a logical I output, and that SUBTRACT refers to a logical 0 output, the following operation is desired when the Y-increment has been detected:

I. ADD, if Z=0 and X=Y.

2. ADD, lfZF-Q and XfY.

.3. SUBTRAC'I', ifZ O and X did not equal Y when 2 was equal to 0, and X=Y.

4. SUBTRACT, if 2 7 0 andX was equal to Y when Z was equal to 0, and X=Y.

5. ADD, if Z a 0 and X did not equal Y when 2 was equal to 0, and X 2 Y. 6. ADD, ifZ s 0 and X was equal to Y when Z was equal to 0, and X=Y. It will be noted that these verbal logic statements describe the quadrantal relationships of the X and Y increments, plus the count condition Z of accumulator 88.

Referring now to the detailed schematic of FIG. 5a, the necessary control logic for up-down control 102 is effected by the interconnected NAND gates and inverters 106, 115 plus AND gate 107. In practice, inverters I06, 115 may be constructed readily from NAND gate circuits by connecting the input leads together.,.NAND gates 103, I04 receive the indicated input signals from X-quadrature converter 38 and Y- quadrature converter 86. Outputs from nAND gates I03, I04 are provided to NAND gate to effect an EXCLUSIVE OR function. The operation of NAND gates I03, I04 and 105 is expressed Iggically as:

X Y+X Y=C where C is the output condition of NA ND gate 105. The various combinations of 'X,X,Y and Y reflect the possible quadrantal conditions in the XY coordinate system; thus requirements 1 and 2-that the signs of X and Y be known, are satisfied.

The third basic condition-that that the zero or nonzero state of accumulator 88 be knownis satisfied by combining the output of AND gate 107, which functions as a zero recognition detector or the condition of the stages in accumulator 88, with C and C in NAND gates 108 and 109, respectively. When the carryouts of counter stages 89, 90, 91, 92 and 93 all are zero, so as to make AND gate 107 have output, the output A from AND gate 107 is combined with C and C signals via NAND gates 108 and 109, and the resulting signals are passed to cross-coupled NAND gates 110 and 111 which supply the necessary memory functionsexpressed as:

1f the memory term is defined as O where N1 indicates the condition of the memory, a very general logic expression may be written for the output states corresponding to addition and subtracti on:

Outputs Q and Q are combined with C and C, respectively, in

NAND gates

112 and 113, the outputs of which are logically combined in NAND gate 114. The three NAND gates 112. 113 and 114 comprise a two-stage NAND circuit equivalent to the AND-OR function. The output of NAND gate 114, which constitutes the ADD or ADD control signals, as well as the inmed output through inverter 115 which serves as the SUB or SUB control, are thus determined by the sign of the X signal from X-encoder 20, the sign of the Y signal from Y-encoder 25, and the zero or nonzero output condition of accumulator 88.

While the complete logic expressions for the ADD and SUBTRACI control functions may be written in expanded form, the following simplified expressions apply with respect to the C and Q variables-.

ADD=C QlC Q=1 The memory element NAND gates 110 and 111 are set so that the output of 110 is Q and the output of 111 is 6 when a zero signal is received i r om AND gate 107. This conditi on co r responds to C and A inputs to NAND gate 108, and C and A inputs to NAND gate 109, plus subsequent NAND inversion. lf inversion of the C input only occurs, the 0 memory condition follows the C inversion so that control signal ADD is always received at the output terminal of NAND gate 114. Beca t 1se of the Q memory characteristic however, variables C and C occur in opposite sign to Q and Q for the SUBTRACT modes.

Output control signals from up-down control 102 are connected to the respective UP and DOWN control terminals on up-down counter stages 8993 to provide fully automatic control for proper accumulation of the count pulses (the connections shown in FIG. are merely illustrative). Forward or UP" counting occurs when the ADD control signal from output NAND gate 114 is a logical l; the invert or logical 0 is applied from inverter 115 to the DOWN" control terminal. Reverse or DOWN counting takes place when the ADD control signal from NAND gate 114 is logical 0 and is inverted so as to appear as a logical 1 at the DOWN" terminal of updown counter stages 89-93.

When using the fully automatic arrangement shown in FIGS. 5 and 5a, the operator has only to position the cursor 14 (FIG. 1) on the boundary l3, reset all up-down counters to establish the origin of the X-Y system, carefully move the cursor 14 around the boundary 13 for one complete traverse, and then read the area on the display 37. Reversals of direction in the movement of cursor l4 introduce no error into the area indications provided the boundary of area 13 is followed carefully; in fact, excursions from the boundary are permissible provided the motion is carefully retraced.

It will be understood, of course, that the NAND functions are employed for constructional convenience; AND and NOT functions, OR and NOT functions, and NOR functions may be utilized within the scope and intent of the invention. Similarly,

positive or negative logic. as well as mixed logic, may be employed without departing from the novelties and advantages of the invention.

The display apparatus illustrated in block diagram form in FIGS. 3 and 4 may comprise any suitable apparatus that will accept digital information and convert that information into a visual set of numbers indicative of the area being traversed by the cursor. For example, a suitable display device would be a series of Nixie tubes arranged to receive the accumulated data in accumulator 88. The display means could preferably be controlled by the command pulses emitted from the Y quadrature converter such that the area measurement was displayed each time the accumulator unit was updated.

Although preferred embodiments of the invention have been described in such detail as to facilitate reproduction by those skilled in this art, such description is to be considered il lustrative rather than limiting for the invention may be altered by the substitution of other components than those described herein without departing from its fundamental concepts and the spirit of the subject invention.

lclaim:

1. An area measuring apparatus. comprising:

cursor means for traversing the boundary of a two-dimensional figure forming the area to be measured;

encoding means including first encoding and converter means for generating signals representing the movement of the cursor means along the boundary of the figure only in a first coordinate direction, second encoding and converter means for generating signals representing the movement of the cursor means along the boundary of the figure only in a second coordinate direction. the signals from the second encoding and converter means being command signals produced at each traversal by the cursor means of a unitary distance in the second coordinate direction,

accumulating and registering means for storing the encoder signals and computing the area of the figure, including reversible register means for temporarily storing encoding signals representative of the cursor movement in a first coordinate direction. down counter means for periodically receiving the stored data in the reversible register means and for providing the quantitative value of the stored data. accumulator means for receiving and accumulating pulsed signals representing the quantitative value of the stored data;

control means regulated by the cursor movement in one coordinative direction for generating timing and clock signals to operate the accumulating and registering means; and

display means for indicating instantaneously the accumulated data in the accumulating and registering means representing the area of the measured figure.

2. An area measuring apparatus according to claim 1 wherein the control means further includes clock generating means for providing periodic pulse signals and timing means for generating a transfer signal for transferring data from the reversible register means to the down counter means in response to a command signal from the second encoding and converter means.

3. An area measuring apparatus according to claim 2 wherein the timing means includes gating means for simultaneously transferring the periodic pulse signals to the down counter means and the accumulator means.

4. An area measuring apparatus according to claim 3 wherein the accumulating and registering means further comprises gating means responsive to the zero condition of the down counter means for controlling the timing gating means.

5. An area measuring apparatus according to claim 3 wherein the timing means is responsive to the periodic clock signals and to the command signals from the second encoding and converter means to pro ide synchronized periodic pulse signals, and comprises means responsive to the synchronized periodic pulse signals for generating additional control signals coding and converter means and to the condition of the accumulator means for operating the accumulator means in either an add or a subtract mode. 7 a l 7; An area measuring apparatus 'according to claim 6 wherein the up-down control means includes NAND gating means responsive to the signals from the first and second encoding and converter means, AND gating means responsive to the condition of the accumulator means, and means responsive to the output signals fromthe NAND and AND gating means for generating up and down control signals for operating the accumulator means.

8. An area measuring apparatus for measuring the area of two-dimensional figure, in combination, comprising:

cursor means for traversing the boundaryof said figure, accumulating and registering .means for computing the area of the two-dimensional figure in response to pulse signals representative of the movement of the cursor means along the boundary of the two-dimensional figure in a first and second coordinate direction; the accumulating and registering means including reversible register means for storing the pulse signals representing the boundary dimension in the first coordinate direction, down counter means for periodically receiving the stored data in the reversible register rneans, and accumulator means for receiving and accumulating digital signals.

representing the quantitative value of the stored data in the reversible counter means; control means including clock pulse'generating means for providing repetitive pulse. signals and timing means for LII generating a transfer signal to transfer data from the reversible register means to the down counter means in response to the pulse signals representing a unit dimension of the boundary in the'second coordinate direction. said control means being regulated by the cursor movement; and I display means for instantaneously indicating the accumulated data in the accumulatormeans representing the area of the measured figure.

9. An area measuring apparatus according to claim ll wherein the timing means includes gating means for simultaneously transferring the repetitive pulse signals to the down counter means and the accumulator means.

10. An area measuring apparatus according to claim 9 wherein the accumlating and registering means further comprises gating means responsive' to the zero condition of the down counter means for controlling the timing gating means.

It. An'area measuring apparatus according to claim [0 wherein the control means further includes up-down control means responsive to the pulse signalsrepresentative of the boundaries of the two-dimensional figure and to the condition of the accumulator means for operating the accumulator means in either an add or a subtract. mode.

10. An area measuring apparatus-according to claim 9 wherein the accumulating and registering means further comprises gating means responsive to the zero condition of the down counter means for controlling the timing gating means.

11. An area measuring apparatus according to claim 10 wherein the control meansfurther includes up-down control means responsive=to the pulse signals representative of the boundaries of the two-dimensionalfigure and to the condition of the accumulator means for operating the accumulator means in either an add or a subtract mode.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 571 932 Dated March 23 1971 lnvent r( John G. Peddie It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 20, "register to permit" should read register stages to permit Column 6 line 65, "nAND" shoul read NAND Column 7 line 1 "that that the" should rea that the line 4, "or" should read for line 14 u u h "Q should read Q line 18, ADD A+A Q 5 cu read ADD A+A Q line 19, "SUB A Q should read SUB A Q Signed and sealed this 9th day of November 1971 (SEAL) Attest:

EDWARD M. FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Acting Commissioner of Pate

Claims

1. An area measuring apparatus, comprising: cursor means for traversing the boundary of a two-dimensional figure forming the area to be measured; encoding means including first encoding and converter means for generating signals representing the movement of the cursor means along the boundary of the figure only in a first coordinate direction, second encoding and converter means for generating signals representing the movement of the cursor means along the boundary of the figure only in a second coordinate direction, the signals from the second encoding and converter means being command signals produced at each traversal by the cursor means of a unitary distance in the second coordinate direction; accumulating and registering means for storing the encoder signals and computing the area of the figure, including reversible register means for temporarily storing encoding signals representative of the cursor movement in a first coordinate direction, down counter means for periodically receiving the stored data in the reversible register means and for providing the quantitative value of the stored data, accumulator means for receiving and accumulating pulsed signals representing the quantitative value of the stored data; control means regulated by the cursor movement in one coordinative direction for generating timing and clock signals to operate the accumulating and registering means; and display means for indicating instantaneously the accumulated data in the accumulating and registering means representing the area of the measured figure.

5. An area measuring apparatus according to claim 3 wherein the timing means is responsive to the periodic clock signals and to the command signals from the second encoding and converter means to provide synchronized periodic pulse signals, and comprises means responsive to the synchronized periodic pulse signals for generating additional control signals for the timing gating means and for generating the transfer signal.

6. An area measuring apparatus according to claim 3 wherein the control means further includes up-down coNtrol means responsive to the signals from the first and second encoding and converter means and to the condition of the accumulator means for operating the accumulator means in either an add or a subtract mode.

7. An area measuring apparatus according to claim 6 wherein the up-down control means includes NAND gating means responsive to the signals from the first and second encoding and converter means, AND gating means responsive to the condition of the accumulator means, and means responsive to the output signals from the NAND and AND gating means for generating up and down control signals for operating the accumulator means.

8. An area measuring apparatus for measuring the area of two-dimensional figure, in combination, comprising: cursor means for traversing the boundary of said figure, accumulating and registering means for computing the area of the two-dimensional figure in response to pulse signals representative of the movement of the cursor means along the boundary of the two-dimensional figure in a first and second coordinate direction; the accumulating and registering means including reversible register means for storing the pulse signals representing the boundary dimension in the first coordinate direction, down counter means for periodically receiving the stored data in the reversible register means, and accumulator means for receiving and accumulating digital signals representing the quantitative value of the stored data in the reversible counter means; control means including clock pulse generating means for providing repetitive pulse signals and timing means for generating a transfer signal to transfer data from the reversible register means to the down counter means in response to the pulse signals representing a unit dimension of the boundary in the second coordinate direction, said control means being regulated by the cursor movement; and display means for instantaneously indicating the accumulated data in the accumulator means representing the area of the measured figure.

9. An area measuring apparatus according to claim 8 wherein the timing means includes gating means for simultaneously transferring the repetitive pulse signals to the down counter means and the accumulator means.

10. An area measuring apparatus according to claim 9 wherein the accumulating and registering means further comprises gating means responsive to the zero condition of the down counter means for controlling the timing gating means.

10. An area measuring apparatus according to claim 9 wherein the accumlating and registering means further comprises gating means responsive to the zero condition of the down counter means for controlling the timing gating means.

11. An area measuring apparatus according to claim 10 wherein the control means further includes up-down control means responsive to the pulse signals representative of the boundaries of the two-dimensional figure and to the condition of the accumulator means for operating the accumulator means in either an add or a subtract mode.