DE2223256A1 - Visual display controller - Google Patents

Description

Please state our reference in the answer

I / p

INTERNATIONAL COMPUTERS LIMITED, ICL House, Putney, London,

S.W. 15, England

Display controller

The invention relates to display controllers and, more particularly, to devices for controlling the drawing of lines on a visual display surface by continuously moving a point as a function of changing position signals with respect to a coordinate axis of a coordinate system, whereby the position values are continuously updated.

Apparatus has been proposed for recording visual indications on the screen surface of a cathode ray tube by selectively shifting the electron beam of the tube. Such a device has often been used in connection with a computer, and for example, when a recording operation is carried out, the course to be recorded by the movement of the beam is continuously increased in increments of the displacement of the

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May 10, 1972 W / He - 2 - I / p 74l4

Ray in each of two orthogonal axes, the X and calculated on the Y-axis. In other cases, the scheme to be drawn is computed and stored in a storage device as one Series of displacement values saved for each line to be drawn.

According to the invention there is featured an apparatus for controlling the drawing of curved lines on a display surface by means of generating an initial pair of values, one for each axis, which is the product represent the radius of the desired arc and the sine of the displacement angle θ over which the radius is around shifted an incremental distance along the sheet to be drawn becomes, and the product of the radius and the cosine of the displacement angle Θ, where the value pair by the incremental distance is expressed in binary code with η value digits, a device for temporarily registering the Value pairs, a device that independently for each axis increases the registered value for one axis by n + 1 value places shifted to the right and the registered value for the other axis shifted by n / 2 value places to the right, arithmetically accumulates, a device that is derived from the accumulation device V / er from the n / 2 value places of the highest importance extracted, where the extracted values are used to

to determine a level of the arc to be drawn for the coordinate axes, as well as to determine the temporarily registered Fourth to modify the same axis, and a device for controlling repeated successive operations the accumulating device, the extracting device, and for Giving up the extracted values in order to determine successive steps of the sheet to be drawn.

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The invention is described below in conjunction with the drawing explained using an exemplary embodiment. Show it:

Fig. 1 is an explanatory diagram,

2 shows a schematic representation of a register arrangement for controlling the achievement of beam position fourths, and

FIG. 5 is a schematic block diagram of a viewing display device. :

Before the device according to the invention for controlling the visual display of curved lines on the screen of a cathode ray tube is described in detail, be briefly on the

at
Received requests for such a device. When lines are drawn on the display screen of a cathode ray tube, such lines are formed by shifting the electron beam of the tube, and the thickness of the drawn lines depends on the resolution of the display area of the spot formed by the beam. Since this spot has a limited size, it is useful to consider the beam displacement when drawing a line as a function of the spot resolution. The dimensions of the figures to be drawn and thus the degree of displacement required for the beam are most simply expressed in increments of a size which corresponds to the spot resolution.

Thus the Great puts this growth shares the demands door digital definition of the spot position addresses required for determining the beam moving over the display area.

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In patent application P (our file i / p 7 ^ 10 of

on the same day) a device for drawing straight lines is described and illustrated, in which the beam position values are expressed in binary code representation, and in which these values are decoded into analog signals in order to control the positioning of the cathode ray at the position whose address is determined in a pair of position registers, one for each of the two orthogonal axes; curved lines can be drawn by a similar beam positioning system. When drawing an arc, however, the incremental change in the address value in a position register for each drawing step must be such that a chord that is drawn by the beam movement does not deviate from the theoretical true curved path which is greater than or as great as the minimum resolution distance between is two adjacent spot positions. In a practical case, the incremental distance is made equal to the spot resolution of the cathode ray tube, and the maximum difference in position between the chord actually drawn by the beam movement and the real curved path must be smaller than such incremental proportion. In the device according to the invention, the radius of the arc is expressed in these incremental fractions, and it is assumed that the maximum radial value for an arc, which can be expressed in a binary code register, is determined by the binary value place capacity of the register and awei 2 ⁿ - l
is.

2 -1, where η is the value place capacity of the register

The error between a drawn tendon and the real bow depends on the imaginary angle over which the radius for every drawing step is shifted, and it can be shown that the maximum permissible error for any circle of an increase in an imaginary radial angular movement oil occurs in such a way that the sine of half the angle

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0 is equal to the value (2R-I) ¹ Z ² ZR, where R is the radius. If R becomes large with respect to the change in angle, it can

1/2 τ / 2
Limit value can be taken as 2 (2) ' / R ' , this value is always smaller than in the theoretical case, and in practice this expression can also be simplified further with certainty. As mentioned above, the maximum value of R, which is expressed in Binärcodedarstellung, 2-1 .. However, if this maximum value is taken to 2 ^n, the critical angle can .with security than 2 (2) ^1/2 / 2 ^{ri / 2} can be assumed for the case of a maximum expressible radius.

If one has reached a safe value for the angular increase 0, expressed by R, it is now desirable to express growth components of axial deflection that do not result in an unacceptable growth component, also expressed in R. The two axes of translation are referred to as the X-axis and the Y-axis, as shown in FIG. This figure shows the condition in which an occupation of a radius from a point a to a point b sweeps an arc. From this figure it can be seen that the changes in the X and Y axis values, namely Δ X and Δ Y from the movement of the radius over an angle increment 0 from an initial position result at an imaginary angle θ with respect to the X axis . The entire angular movement is of course exaggerated for the sake of better illustration. The change A Y can be expressed as Y- ¹ (1-Cos 0) + X ^! sin 0 , where Ϋ ^{1 is} equal to R sin θ and X ^{1 is} equal to R cos θ. Similarly, the change Δ X can be expressed as Y sin 0 - X ^f (1-cos 0) .

the solution

With / these equations for obtaining values for the incremental changes in the X and Y-axis position values, it is necessary to include progressively higher terms of an expression for the incremental angle 0. Provided, however, that an error caused by arbitrary termination of the

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Progression is generated, no beam deflection results, which is greater than an increase in the resolution when drawing a complete circle, the solutions can can be simplified considerably. Furthermore, for reasons of expediency for the facility to be described, the terms used for the calculation must be rounded Binary coefficients are expressed.

It can be shown that if the values of ^ X and AY are assumed to be Y0-X0 / 2 and X0 + YJZT / 2, a complete circle of the accumulated error for a quadrant is enlarged with an increase in η (i.e. a decrease in 0) and tends to -F / 6, where F is a constant defined by 0 = Έ / 2 ^η ' when 0 becomes very small. Under these circumstances, the total accumulated error in drawing a complete circle cannot exceed -4F / 6, and if the requirement that this total error be less than an incremental fraction is taken into account with respect to the contents of a binary register containing incremental fraction values this expression must be solvable, hence a value

ρ smaller than one is obtained. Thus the value for F must not exceed 1.67 so that F cannot exceed 1.225. If the value for F is now assumed to be 1, the value for 0.1 / 2 is ⁿ ', as indicated above ^ where η is the value place capacity of the binary register. Using this expression l / 2 ⁿ / ² for 0, the values for Δ X and ΔY used when drawing an arc become

& Y = X / 2 + Y / 2 ^{n + 1} , and
AX = Y / 2 - X / 2 ^{n + 1} ,

expressed in the values of the register. Thus, assuming that a first starting position for the arc is used as the X and Y axis values should be expressed by the radius of the arc to be drawn relative to a starting angle θ,

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which lies within a predetermined quadrant of FIG. 1, the values X = RcosQ and Y = RsinQ can be calculated and divided into two. Multi-digit binary registers are held. For example, in the case of the ^ Y value, it can be seen that the term X / 2 ⁿ 'can be derived by dividing the starting value in the X register by the kbenz of 2 equal to half the capacity of the register, and that this division is equivalent to shifting the contents of the X-axis register by half the capacity to the right. Moreover, the term Y / 2 ^{rl: f} 'is equivalent to shifting to the right by η + 1 places, where η is the Y-axis register capacity. These two expressions can thus be derived by appropriately shifting the contents of the registers to the right, and the values thus obtained are added to or subtracted from the values in the registers, as required by the corresponding equations above. This process then results in the desired modification of the position values for controlling the electron beam displacement for drawing an incremental portion for the sheet, and it results that this modified fourth then becomes the starting point for drawing the next incremental portion of the arc. This derivation and the oiling process are continued until the bow is completely drawn. '

Fig. 2 shows an arrangement of registers for performing this process of derivation and summation. Two sheet value registers 31 and 32 are for the X and Y axis values, respectively intended. In the present case, each sheet register "5Ij 32" has eight binary value places and has Input channels 33 and output channels 34. In practice is the number of value points is not limited to eight. An adder 35 is the X-axis and a similar adder 36 is the Y-axis assigned? both adders have input and.

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Output channels "57 and" 58, the output channels 38 with the adding output registers 39 and 40 for the X and Y axes are connected. The adder output registers are designed so that they selectively form the fourth correctly or in two's complement the output channels 44 feed. An accumulator 7 is provided for the X-axis and has a part 7a of higher importance on, which in the present case has four places of value, as well as a part 7b of lesser importance with nine places, where half of the hollow meaning referred to as ÄX register while half of the less important is used to record the residual X incremental values. A similar accumulator 17 is intended for the Y-axis. Outputs from the ΔΧ register 7a and the ΔΥ register 17a are transmitted via transmission paths

41 given to the X and ϊ position registers 5 and 15. The Output channels 34 from sheet registers 31 and j52 become connected to the input channels 37 of the adders 35 and 36.

The adders 35 and 36 receive outputs from the arc registers 31, 32 of the same axis from the channels 34, and the four least significant digits of the adders 35 * .36 also take inputs from the & X and & Y registers 7a and 7a 17a on. The values which represent the sums of these input values are passed by the adders 35 , 36 into the output channels 38, which are connected to the output registers 39 »40 in a corresponding manner. Output channels 44 from output registers 39 * 40 of each axis are connected to input channels 33 of X-arc and Y-arc registers 31 and 32, and also to input channels 43 of registers 7 and 17 of the same axis. The same channels 44 from registers 39 and 4o are also with input channels

42 of registers .17 and 7 of the opposite axes are connected.

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The connections to the channels 42 are designed in such a way that values from the register 39 are, for example, four value places to the right before they are introduced into register 17. The four value positions of higher importance of the value in the Output registers "59 are introduced into the ΔΥ register 17a, while the rest of the valuation values are of lesser importance in the value places of highest importance of the remaining part of the Y-axis register 17 are introduced. This arrangement of the connections results in the desired shift to the right equal to half the capacity of the X-arm register. Similarly, values are obtained from the Y-axis output register 14 in the X-axis register 7 with a shift introduced by n / 2 value points that are given to them.

The connections between channels 44 and 43 are designed in such a way that they result in a shift of n + 1 value places to the right when transferring values from registers 39 > 40 in the remaining ΛΧ and Z \ Y registers, so that the Values from the adders 39, 40 are actually introduced into the least significant digits of the register parts 7b and 17b.

During operation, the initial values for X = Rcos9 and Y-sinG introduced into the X-arc and Y-arc registers 31 and 32, which indicate a first starting point for an arc to be drawn.

Together with the values that are stored in AX and AY register parts 7a and 17a (which are zero at this stage)

are the initial values from the X-arc and Y-arc registers 3I and 32 are summed and placed in output registers 40 and 40. The values from registers 39 and 40 become first introduced into the accumulators I7 and 7, which corresponding to the opposite axis, and

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with a shift to the right of n / 2 places. At this stage make the fourth, which is now in the register parts Yes. and 17a are present, incremental changes that the

η ^ 2 current beam position equal to the first expressions Y / 2 ^/

η / Ρ
and X / 2 'of the expressions for X- and Y, as indicated above, are given up, and they are also transferred to registers 7 and 17 in a second working phase, with the n + 1 position shift to the right (set these values represent the second terms X / 2 ^{n + 1} and Y / 2 ^{n + 1 of} the AX and ΔY terms). Thus, the transfer of the values from registers 39 > ^ O brings the X-arc and Y-arc registers 31>

ver—
32 up-to-date and / complete the change for the values in registers 7 and 17 * so that the end of the first percentage of sheet drawing growth is indicated. This point on the line to be drawn will now be the starting point for the second incremental component, and the values in output registers 59 and 40 will be changed by adding the values in the ^ X and JÄY registers to the X-arc and Y-arc registers. Registers 31 > 32 updated. The ΛΧ and A Y registers ¹ Yes. and 17a are cleared, while register parts 7b and 17b can continue to accumulate the remaining incremental components. Dajtfnn a new add and carry cycle is performed. These cyclic operations of inserting, adding, carrying and deleting are repeated until the sheet is completely drawn.

From Fig. 1 it follows that for the first, drawn Quadrants, the X-axis values progressively increase while the Y-values decrease; the progressive gain or loss of values for the respective axes depends on the quadrant that is being drawn. The output registers 39 and 40 (FIG. 2) contain means for selectively complementing the values applied via the channels 44.

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The selection of real or complementary transfer of values is carried out depending on the respective quadrant, in which the arc to be drawn lies, so that the £ »X and ^ Y values have positive or negative form, depending on the way it is required to draw the bow.

The AX and A ^ values are placed on the X and Y position registers 5 and 15 are transmitted over lines 41, and this transmission path includes adding the transmitted values to those that are continuously entered in the position registers 5i 15 are available so that the position values are continuously changed. The position registers are in practice with coupled to the control circuit for deflecting the cathode ray, so that the beam position can be modified depending on the changes caused by the AX and Δ Y registers? A and 17a are registered. The change of the values in registers 7 and 17 for each incremental proportion the beam movement effectively makes a number of addition acts required, e.g. one for registering 59 and 40 to bring up to date, more for adding the first and. second term of the A X and Δγ expressions perform in the manner described above and the X and Y arc registers 31, 3? to bring up to date. The transfer of values from the registers 7a and 17a in registers 5 and 15 with. the cyclical sequence synchronized and takes place after appropriate adding stages.

Another embodiment for drawing curved lines by the same method is shown in Fig. 3, which will be explained below. The lines are drawn on the screen of a cathode ray tube 1 by the electron beam of the tube 1 under the control of Signals itejesehoben is raised, d, Ψ er schiebsei ekt clear, in the conventional way e ^ abandoned

8 9

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will. The electrodes 2 receive signals from an X address decoder 3 and a Y address decoder 4, which are conventional digital-to-analog converters with binary code. Binary-coded position addresses are given to the decoders 3 and 4 through X and Y position registers 5 and 15. X and Y registers 7a and 17a are provided which are coupled to position registers 5, 15 through adders 6, 16 for the X and Y axes so that d X and AY values are entered into position registers 5> 15 can be added to change the beam position of the cathode ray tube 1.

In the ΔΧ and Λγ registers 7a and 17a values from the four most important value places of the accumulators 13 and 23 are transferred, each of which has thirteen positions in total. The accumulators 13 and 23 receive inputs from the input gate groups 11, 12, 21 and 22, which are related to the expressions X / 2 ⁿ - ^{/ 2} : X / 2 ^{n + 1} , Y / 2 ⁿ ' ^{/ 2} and Y / 2 deal ^{n + 1.} The gate group 11 thus has eight outputs, which are respectively connected to the first to eighth position of the accumulator 23, the gate group 12 has eight outputs which are respectively connected to the sixth to thirteenth position of the accumulator I3, the gate group 21 has eight outputs, which are correspondingly connected to the first to eighth position of the accumulator I3, and the gate group 22 has eight outputs which are connected to the positions 6 to I3 of the accumulator 23.

The gate groups 11 and 12 are with their inputs together via a selective complementing unit 10 with the corresponding Outputs of an eight-digit X-arc register 8 connected, while the gate groups 21 and 22 with their inputs. are connected in a similar manner to a Y-arc register 18 via a complementing unit 20. The values are first from a processing device 30 into the X-arm register

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and Ϋ-arc registers 8 and 18 introduced »Subsequent Changes in the X ^ Arc and Y-Arc register values WeMen About Gatter-Addierwäke l4 and 24 of the fermenting from the four Places of utmost importance of the accumulators 13 and 2.3 uii ^ ter Control of a Bogensteüereihheit 26 abandoned that too Control signals for determining the mode of operation of the gate groups 11, 12, 21 and 22, the adders 6 and 16, the complete tierwerke 10 and 20 and the / ^ X and ΛΫ registers 7ä and 17a gives * The networks 14 and 24 are adder networks j of where the X and Y arc registers 8 and 18 output registers represent, and the networks have output gates on j with it a sum value can be introduced into these output registers 8 and 18. Thus the networks 14> 24 also switched in such a way that the values in registers 8, - 18 also second Form entrances.

The ÄX-ündAY registers 7, 17 have Örenz display devices 9 and 19, which are assigned to their ÄusgangsSleltühgen accordingly. The display devices' record 9 and 19 .Are accumulating Komparatoreni also inputs of a Radiüsregister? 3 * RadiUsr.egister speiöhert rush value of the radius of the to be drawn Bögens is j and the display devices 9 and I9 are jev arranged / Eils so, that they result in a display for the control unit 26 * if the accumulated displacement of the corresponding axis is within an incremental proportion of the arcuate radius, so that the completion of the drawing of a quadrant of a circle is displayed. '■

Since the display devices 9 and I9 indicating the completion of a quadrant, 'they .rönnen · other forms-accept ₄ For example, a modified embodiment consisting of a Änzeigevorriehtong of an array of Giattern * ■ which the · stages of the X or Y arc-register assigned

9 8 4 8/1089 BATH *

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and which are designed in such a way that they - the approximation of the value show in register to zero.

The radius value for register 25 is obtained from a display pelcher 28 which also gives indications of the initial beam position for entry into position registers 5 md 15 and the imaginary starting angle θ in the particular quadrant for which the arc is to be drawn, the latter Information is given into the processing device 30. The processing device 30 provides the quadrant information so that the control unit 26 selects the mode of operation of the complementing units 20 and 10, so that the values fed to the accumulators 13 and 23 are in real or complementary form - so that the multiple values can be added or subtracted as a function thereof whether the axial values increase or decrease as you pull the bow.

In operation, the initial beam position values in the registers 5 and 15 are introduced from the memory 28, which also contains the information for the initial, imaginary angle θ for the processing device 30 and the radius value for the radius register 25 results in »The radius value is also entered in the processing device .30 introduced the X> and Y values, RcosG and Rsin9 are calculated and these values are put into the X and Y arc registers 8 and l8 introduces »

The first step of VerSehiebebereehnüng is now carried out under the control of the unit 26, which the gates Ü and 21 and the complementing _{units 1O 1} 2Ό acted upon so that the values from the registers 8 and 18 / in real or complementary form, in the accumulators 23 and 21 of the opposite axis can be introduced, which in view of the registers' 7a and 17a is an effective shift to the right by four places

2 0 § Ο 4 8 / 10i §

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May 10, 1972 W / He - 15 - I / p

corresponds, so that the first expressions for the Δ X and Λ ^T YV erte are added in the accumulators.

The next calculation step is carried out in a very similar way carried out. The gates 12 and 22 are set in a certain state and in the gates 11 and 21 this becomes certain State canceled. The complementing works 10 and are selected as desired and the values from the X and Y arc registers are stored in the accumulators IJ and 23 of the same axis corresponding to an effective displacement to the right by nine places, so that the second expressions of the X and Y values in the accumulators and 23 are added.

The third step now follows, in which the complete four value places of greatest importance of the Δ X and Λ Y values are transferred from the accumulators 13 and 23 to the A X and Δ Y registers 7a and 17a. At the same time, the networks 14 and 24 are set in such a state that these values can be fed back into the X-arc and Y-arc registers 8 and 18 so that the values are brought up to date there. While the registers 7a and 17a are shown in the present embodiment, they are not necessary for a simple arrangement for drawing sheets, but in a practical case allow drawing sheets to be performed in conjunction with other display arrangements. Thus, for a simple application, the Λ X and A Y values can be transferred directly to position registers 5 and 15.

In the present case, however, the Δ X and Δ Y values become off registers 7a and 17a into position registers via adders 6 and 16 are transmitted to change the position register values, thereby shifting the cathode ray in such a way that that an incremental portion of the bow is drawn. ' The / i X and

209848 /. 1.089
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AY values are also introduced into the limit indicators 9 and 19. The transmission of the Δ X and $ Y values can of course take place while a new incremental value is being formed in the accumulators 1.3 and 23, or this transmission can take place as a fourth step of the calculation cycle. In addition, the registers 7a and 17a deleted before new Δ X and .DELTA.Y values are formed.

The above-described operations are repeated until one Draw; the arc is terminated because it has reached an end point; the end point is in the stored information which is related to the sheet. Where the end of a quadrant is indicated by the display devices 9 or 19 is, the drawing of the sheet is continued in the required manner, the selection of the complementing works 10, 20 is but changed to suit the new conditions for increasing or decreasing axial values.

In the example shown, in which the display devices 9 and 19 are connected to the registers 7a and 17a, if the arc begins at an intermediate point within a quadrant, the initial value must be present in the boundary display devices 9, 19 in order to be a real one Display of the end of the Quadrante'n is obtained. Indicators 9 and 19 are prepared in this case with the initial X and Y position values being entered into the sheet registers. One of the display devices then accumulates the successive displacement values in order to reach the radial value at the end of the quadrant. If, as already stated above, the display devices 9 are supplied to the registers 8, 18, this problem does not arise. In the preceding example, for the sake of clarity, it has been assumed that the value of R

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May 10, 1972 W / He - 17 - l / p

in the form of binary value places, which are necessary for the printout, is constant, and that the register value place capacities be chosen so that they correspond to this value. A consideration shows, however, that values for R must be taken into account that contain significant and insignificant bits, by setting the displacement conditions of the system.

In the case of a system designed for a maximum of, for example, η bits, in which n 'significant bits are present, the values representing the expressions X / 2 ⁿ / ² and Y / 2 ⁿ / ² make a correction in the This would require a left shift of n-n '/ 2 digits for the one described, and this left shift can effectively be achieved by changing the amount of right shift that the values apply to during the transfer the accumulators are abandoned. For example, the gate groups 11, 12, 21 and 22 may contain arrangements for achieving the appropriate shift to the right depending on the particular sheets to be drawn. In this case, the appropriate amount of the shift can be specified or calculated by the processing means j50 before every bow is drawn. The expressions X / 2 ^{n + 1} and Y / 2 ^{n + 1 also} require a shift to the left by nn ^! Set so that a comparable correction is made. When n ^{1 is} odd, these left shift corrections are set to become (n-n'-1) / 2 and n-n'-1.

Other modes of operation are possible by further modifying the relative displacement requirements. For example it may be necessary to use the arch in multiple increments that are shorter than the previously noted maximum length. Then the multiple incremental proportion with m Bits' specified. The relative shift to the right for the

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May 10, 1972 W / He - 18 - I-p

Expressions X / 2 ⁿ 'and Υ / 2 ^{Π /} is n.-m places, and another shift to the right of n ^! -m + 1 digits are required for the expressions X / 2 ^{n + 1} and Y / 2 ^{n + 1} .

In all cases, however, it results that the two expressions mentioned above can be achieved by shifting the
RsinQ and Rcosö values are initially obtained and entered into the arc registers. These shifted values are accumulated in the registers which are assigned to the corresponding axes, so that incremental values for changing the current beam position values are formed for each step of the sheet drawing, and the incremental values continuously obtained
are returned to the. Initial values in readiness
for the derivation of each subsequent new step.

209848/1089

Claims (8)

222325Θ 10.5.1972 V / He - 19 - I / p 7 ^ 14 Claims: ' Tiy device for controlling the drawing of curved lines on a display surface by continuously moving a point as a function of changing position signals with respect to a coordinate axis of a coordinate system, the position values being continuously updated, characterized by a device (30, 8 ., 18), which generates an initial pair of fourths, one for each axis, which represent the product of the radius of the desired arc and the sine of a displacement angle θ over which the radius is displaced by an incremental distance "along the arc to be drawn , and the product of the radius and the cosine of the displacement angle Θ, the fourth pair being expressed by the incremental distance in binary code representation with η value places, a device (8, 18) for temporarily registering the value pair, fine device (13 * 23) $ the independent for each axis by the registered value for one axis n + 1 fourth digits shifted to the right and the registered value for the other axis shifted by n / 2 value digits to the right is arithmetically accumulated, a device (7, 17, 14, 24) which takes values from the accumulating device (13 * 23) the n / 2 four digits of greatest importance are extracted, the extracted values being given in order to determine a step of the arc to be drawn for the coordinate axis, as well as to modify the temporarily registered weirs of the same axis, and a device (26) for controlling repeated successive operations of the accumulating means, the extracting means and for giving up the extracted values in order to determine successive steps of the sheet to be drawn. 20 9 8AiM 1 & $ 9 May 10, 1972 W / He - 20 - Tp '? 2. Device according to claim 1, characterized in that a device (10, 20) for controlling 'the arithmetic sign of the shifted ^T / ^r erte is provided, which depends on the particular quadrant with respect to the axes in which to drawing sheet is to be accumulated. 3 «device according to claim 2, wherein the on the screen surface a cathode ray tube is drawn arc to be drawn by deflecting an electron beam, characterized in that, that the extracted values are stored in a pair of position registers (5, 15) j and zv: ar one for each axis of the visual display, with the contents of the position register be decoded so that beam deflection signals for the cathode ray tube are generated. 4. Device according to one of claims 1 to 3 j thereby characterized in that the extracting means comprises summing means (14, 24) for each axis which are converted into one The circulation path from the accumulator device (13 * 23) and the temporary registration device (8, l8) is switched on, the summing means being adapted to feed the extracted values into the temporary registering means (8, '18) added. 5. Device according to claim 4, characterized in that that first and second gate devices (11, 12, 21, 22) are provided for each axis, the values from the temporary recording devices (8, 18) working, with output lines from the first gate device (11, 21) with the corresponding accumulating device (23 »13) on the opposite axis with an effective n / 2 value point shift are connected and output lines from the second gate device (12, 22) with the corresponding Accumulating device (13> 23) of the same axis with one 209848/1089 10. 5.1972 W / He - 21 - i / p effective n + 1 vertical shift are connected. 6. Device according to claim 5, characterized in that the device for controlling the arithmetic sign of values to be accumulated has a device (10, 20) for selectively forming the complement of a given value, the complement forming device (10, 20) between the corresponding temporarily working registration devices (8-, 18) and the gate devices (11, 12, 21, 22) are switched on independently for each axis. 7. Device according to claim 6, characterized in that an arrangement (9, 19 * 25) is provided for indicating the completion of the drawing of a quadrant of the sheet, and that the control device (26) responds to a display from the display arrangement (9, 19 > 25) responds to terminate the selective actuation of the complementing device (10, 20). 8. Device according to claim 7, characterized in that the display arrangement (9, 19, 25) has a device (25) for Registering a radius value representing the arc radius and having a comparison arrangement (9, 19) for each axis, the comparison arrangement being adapted to compare the radius value with successive ones of the extracted values compares to produce a signal indicating the termination of a quadrant when the compared values are less differ from each other than a predetermined value. 9 · Device according to claim 8, characterized in that another register (7a * 17a) between the accumulator (lj5j 23) and the position register (5, 15) for each Axis is switched on, the comparison arrangement (9 * 19) between the radius value register (25) and the further register (7a, 17a), which receives the extracted fourth, is turned on. 209848 / 10B9