EP0014127A1 - Curve generator for making visible symbols on a cathode ray tube screen - Google Patents

Abstract

Device making it possible in particular to develop signals relating to a circular path from simple algorithms. It includes means for calculating (1) a parameter ΔL defined by R = ???? and 0 <= ΔL <U with U elementary vector, ϑ angle at the center of a polygon with side U + ΔL circumscribed to the circle R, and logic processing circuits (2 to 6) developing the polar direction Pn of the plot according to the relation: <IMAGE> The invention applies to systems for displaying symbols on a cathode-ray screen.

Description

The present invention relates to a device for generating curves representing symbols in the form of circles or vectors, with a view more particularly to their display on the screen of a cathode-ray tube.

The invention can thus be applied to cathodic display systems such as, in particular, graphic display consoles and electronic piloting indicator systems.

In these systems, a digital computer supplies data to a curve generating device in order to develop the deflection signals corresponding to the display of the various symbols. The scanning of the tube is of the random type, also called jumper scanning, according to which the current symbol is drawn directly by the cathode ray. The different symbols are displayed one after the other in an order established in advance during an image scan of the tube.

In order to relieve the computer and not to clutter it unnecessarily from the time point of view by repeated calculations and from the volume point of view by high-capacity memories, these systems use, in known manner, a buffer memory which contains the words of the data to view. These words are supplied initially by the computer which then only has to transfer the replacement words corresponding to data modifications. The memory is read at the rate of the image scan of the tube during which all the different data to be displayed is displayed. The data successively extracted from the memory are generally transformed by decoding and applied to the generator of curves.

The curve generator device consists of circuits carrying out operational processing corresponding to parametric equations or algorithms, determined as a function of the various symbols to be displayed made up of vectors, or curves of higher degree such as circle, ell.ipse, conic, or alphanumeric characters.

The generator device according to the invention relates more particularly to the preparation of signals intended for the representation of circular symbols, the device also making it possible to represent linear symbols or vectors. The processing can be analog or logical depending on whether the computer data is converted or not before application to the generator device. Whatever the solution adopted, the resolution of the problem requires circuits that are all the more complex as the refinement, that is to say the precision required for the tracing, is higher, the algorithms corresponding to circles becoming very complex.

An object of the invention is to provide a device for generating curves which allows great precision in the drawing using relatively simple circuits since it results from the implementation of an original drawing method which results in simple algorithms. .

et 0≤ΔL<U où U est la valeur prédéterminée d'un vecteur élémentaire, 0 une valeur prédéterminée d'angle au centre d'un polygone régulier de côté L = U + AL circonscrit au cercle, 0 étant de la forme

, et des circuits logiques de traitement opérationnels groupant, un premier circuit sommateur résolvant x_n = x_n-1 + ΔL.Δ _n-1 - U.Δ_n-1 avec x_o prédéterminé entre 0 et L, un circuit élaborant le facteur binaire Δ_n égal à 1 pour x_n supérieur ou égal à U, un circuit multiplicateur résolvant α_n = x_n-1-

. Δ _n-1, un deuxième circuit sommateur résolvant θ_n = θ_n-1 + θ . Δ _n-1 et un troisième circuit sommateur délivrant la valeur d'angle polaire P = θ_n - a du tracé formé de vecteurs élémentaires successifs se terminant sur le polygone de côté L.According to a characteristic of the invention, there is provided a device for generating circular symbols, comprising digital calculation means developing a parameter ΔL defined by the relationships R =

and 0≤ΔL <U where U is the predetermined value of an elementary vector, 0 a predetermined value of angle at the center of a regular polygon of side L = U + AL circumscribed to the circle, 0 being of the form

, and logical operational processing circuits grouping together, a first summing circuit resolving x _n = x _n-1 + ΔL. Δ _n-1 - U.Δ _n-1 with x _o predetermined between 0 and L, a circuit developing the binary factor Δ _n equal to 1 for x _n greater than or equal to U, a multiplier circuit resolving α _n = x _n-1 -

. Δ _n-1 , a second summing circuit solving θ _n = θ _n-1 + θ. Δ _n-1 and a third summing circuit delivering the value of polar angle P = θ _n - a of the plot formed of successive elementary vectors ending on the polygon of side L.

• - les figures 1 à 3, des schémas relatifs au procédé utilisé dans un dispositif générateur de courbes selon l'invention ;
• - la figure 4 un diagramme général d'un dispositif générateur conforme à l'invention, et
• - les figures 5 et 6, un diagramme d'un exemple de réalisation des circuits logiques de traitement du dispositif générateur,et des formes d'ondes s'y rapportant.

The features and advantages of the invention will appear in the description which follows, given by way of nonlimiting example with the aid of the appended figures which represent:

• - Figures 1 to 3, diagrams relating to the process used in a curve generator device according to the invention;
• FIG. 4 a general diagram of a generator device according to the invention, and
• - Figures 5 and 6, a diagram of an exemplary embodiment of the logic processing circuits of the generator device, and related waveforms.

The trace on the screen of the cathode ray tube is constituted in a known manner by a series of elementary vectors of short length U, constant for the speed of the trace considered. The succession of directions of these successive elementary vectors determines the type of tracing, straight in the case where the symbol to be represented is a vector, curved in the case where it is for example a circle.

The drawing of a circle is carried out according to the invention by seeking to reproduce a regular polygon circumscribed to the circle as shown in Figure 1, whose angle at the center 0 has a predetermined value and whose side is L = U + ΔL with the condition 0≤ΔL <U.

The relationship between the radius R of the circle to be drawn and the parameter L results from R = ^L , the angle at 2 tg 0/2 center 0 being chosen sufficiently small to be able to make the conventional approximations cos θ = 1 and sin θ = tg θ = 0.

déterminant une plage de variation du paramètre R allant de la valeur

comme représenté sur la figure 2.The result

determining a range of variation of the parameter R going from the value

as shown in figure 2.

est égal à 2 et la plage de variation R₀ à R₁ peut s'avérer insuffisante pour les besoins de l'exploitation. Afin d'y remédier, une deuxième plage ou gamme R₁ à R₂ est déterminée,selon l'invention, en considérant une deuxième valeur 02 d'angle au centre de valeur moitié de celle θ₁ initiale correspondant à la première gamme R₀ à R₁. Plusieurs. gammes peuvent ainsi être déterminées successivement en divisant par 2 à chaque fois la valeur de l'angle au centre θ, le rayon maximal étant à chaque fois doublé. Le nombre de gammes est déterminé en fonction de la plage totale de variation à couvrir. La figure 3 représente à titre d'exemple trois gammes pour les valeurs d'angle au centre θ₁,

et

. En conséquence, le paramètre θ peut s'écrire sous la forme

, m étant nombre entier de la forme G +G où G est une constante non nulle et où G varie de 0 à une valeur K prédéterminée, pour produire K + 1 gammes de variation. La première gamme correspond à la valeur

Go et la dernière à

. Le rapport entre les rayons extrêmes de la plage totale de variation

, soit 256 pour K = 7. La résolution pour ΔL est égale à U.2^K.The ratio of extreme rays

is equal to 2 and the variation range R ₀ to R ₁ may prove to be insufficient for operational requirements. In order to remedy this, a second range or range R ₁ to R ₂ is determined, according to the invention, by considering a second value 02 of angle at the center of value half of that initial θ ₁ corresponding to the first range R ₀ to R ₁ . Many. ranges can thus be determined successively by dividing by 2 each time the value of the angle at the center θ, the maximum radius being each time doubled. The number of ranges is determined based on the total range of variation to be covered. FIG. 3 represents by way of example three ranges for the values of angle at the center θ ₁ ,

and

. Consequently, the parameter θ can be written in the form

, m being an integer of the form G + G where G is a non-zero constant and where G varies from 0 to a predetermined value K, to produce K + 1 ranges of variation. The first range corresponds to the value

Go and the last one to

. The ratio between the extreme radii of the total range of variation

, ie 256 for K = 7. The resolution for ΔL is equal to U.2 ^K.

The tracing cannot generally be carried out exactly because it is carried out by means of elementary vectors whose fixed length U is generally different from that L on the side of the theoretical polygon defined previously.

In accordance with the process implemented according to the invention, the condition is imposed that each vector elementary ends at a point belonging to the theoretical polygon of side L considered. By calling x the distance which separates the end of the n ^th elementary vector from the next vertex of the polygon, it is agreed that: when this distance x _n is greater than or at least equal to the value U, the elementary vector of order n + 1 is drawn exactly along the side of the polygon and in the opposite case, that is to say for x _n less than U, the drawing of the vector n + 1 is carried out according to the polar angle of the next side of the corrected polygon d 'an angle θ _{n + 1} .

• - pour
  
• - et pour
  
  et
  

It follows from the above the following relationships:

• - for
  
• - and for
  
  and
  

et x_n = x_n-1 + ΔL.These last two values can be approximated and can be written: α _n = x _n-1 .

and x _n = x _n-1 + ΔL.

It is agreed an initial value x _o for the start of the plot, for example x _o = 2 as shown in FIG. 1 where the plot starts in the middle I of a first side AB of the theoretical polygon of side L.

et

The uncorrected polar angle θ _n of the plot, that is to say the one corresponding to the direction of the corresponding side of the theoretical polygon of side L checks the relations:

and

This angle is corrected by the aforementioned value to obtain the real direction of the plot P _n = θn-α _n .

The parameter θ _n has an initial value θ _o = P corresponding to the polar angle presented by the first side of the polygon. Thus in the case of FIG. 1, the value P is equal to the angle made by the direction AB with a reference direction for measuring the angles, not shown.

The plot algorithm is deduced from the foregoing relationships by using, to facilitate writing, the binary factor Δ _n-1 by convention equal to 1 for x _n-1 ≥U and equal to 0 for x _n-1 <U .

It results in:

où le facteur S est égal à 1 ou -1 selon le sens de tracé choisi.One can notice that the formulation of the angles supposed a tracing according to the negative direction (fig.l) that is to say the opposite direction of the conventional trigonometric direction. More generally can write:

where the factor S is equal to 1 or -1 depending on the direction of the route chosen.

The realization of the curve generator device can be carried out in multiple ways, the essential means responding to the general algorithm of the layout have been symbolized on the general diagram of FIG. 4, disregarding the time synchronization, for the sake of simplification. .

et θ/U qui résultent de calculs simples.Calculation means 1, forming part of an annex digital computer, develop the parameter ΔL as a function of the radius R displayed or programmed and also deliver, the data U and 0 (or m), the angular value initial θ _o and incidentally,

and θ / U which result from simple calculations.

The processing is preferably digital and the corresponding logic circuits comprise; a first summing circuit 2 which performs the summation relative to x _n , a circuit 3 which produces the factor Δ _n by comparison of the values U and x _n , a multiplier circuit 4 resolving a _n , a second summing circuit 5 which produces θ _n and a third summing circuit 6 which delivers the polar angle P _n or real direction of the trace.

The signal Pn is then processed by. known manner in additional circuits, comprising a sine-cosine table 7 which delivers the sin P _n and cos P _n values respectively to integration circuits 8 and 9 whose integration time corresponds to that of the symbol to be traced. This duration is controlled and determined by the computer by using, for example, up-counting means supplied by a clock signal.

In the application to a display system on a cathode screen, the downstream circuits can consist of digital-analog conversion circuits 10 and 11 preceding or following conventional multiplication and addition circuits 12 and 13 to produce the format. and the initial positioning of the route. The operators and the initial coordinates are also provided by the computer. The resulting deflection signals feed beam deflecting members 14 and 15 of the cathode ray tube 16.

A linear vector plot is obtained simply as can be seen by forcing the control value Δ _n of circuits 2, 4, 5 and 6 to 1 so as to keep the polar direction of the plot constant. This can be obtained by a control signal SV supplied by the computer and transmitted through a gate circuit or 17 receiving Δ _n by a second input. The SV signal is value 1 in the case of a vector plot and P _n = θ _o , its value has gone to 0 in the case of a circle plot.

An exemplary embodiment of the logic processing circuits is shown in FIG. 5. It includes a first memory register 20 or waiting register which receives from the annex computer the digital data ΔL, m relating to the radius R as well as the data S of the direction of layout. The data are entered in parallel in the register 20 on reception by the latter of a loading signal S1 (FIG. 6). It is considered that the transferred word comprises eight bits for the data ΔL, three bits for the parameter m defining the angle at the center θ and one bit for the parameter S. A second register 21 constitutes a buffer memory. On receipt of a loading pulse S2 the data ΔL, m and S are transferred to the register 21. From then on, the data relating to the circle or vector symbols can be entered in the register 20.

. Il reçoit ensuite la sortie d'un circuit d'addition 23 lui-même alimenté par la sortie du registre 22 et par la valeur ΔL du registre 21. Le poids des registres 20, 21, 22 est U longueur du vecteur élémentaire. La valeur x₀ est produite à l'aide des sept bits de plus grand poids de AL et d'un bit 1. La commande S3 est appliquée pour initialiser le contenu du registre 22 à x_o puis, la sortie du sommateur 23 reste connectée au registre qui est commandé périodiquement par le signal HΔ_n, H étant le signal d'horloge représenté sur la figure 6. Le facteur Δ_n est produit à l'aide d'un circuit ET 24 d'une bascule PQ 25. L'intégration de l'erreur de longueur ΔL a lieu dans le registre 22. Le débordement de l'intégrateur est mémorisé par le signal S4 dans la bascule 25 qui produit Δ_n. Selon la valeur 0 0 ou 1 de Δ_n-1, le contenu du registre 22 se trouve accru de AL, ou diminué de U et la bascule remise à 0, ce qui réalise bien la première relation de l'algorithme. Le contenu Ml du registre 22 de poids 2°, considéré comme nombre entier représente 2⁸. x_n-1.A circuit 22 grouping a multiplexer and a register is initially loaded at the value

. It then receives the output of an addition circuit 23 itself supplied by the output of the register 22 and by the value ΔL of the register 21. The weight of the registers 20, 21, 22 is U length of the elementary vector. The value x ₀ is produced using the seven most significant bits of AL and a bit 1. The command S3 is applied to initialize the content of the register 22 at x _o then, the output of the summator 23 remains connected to the register which is periodically controlled by the signal HΔ _n , H being the clock signal shown in FIG. 6. The factor Δ _n is produced using an AND circuit 24 of a flip-flop PQ 25. L ' integration of the length error ΔL takes place in register 22. The overflow of the integrator is memorized by the signal S4 in flip-flop 25 which produces Δ _n . Depending on the value 0 0 or 1 of Δ _n-1 , the content of register 22 is increased by AL, or decreased by U and the flip-flop reset to 0, which does the first relation of the algorithm well. The content Ml of the register 22 of weight 2 °, considered as an integer represents 2 ⁸ . x _n-1 .

The other relations of the algorithm are realized by means of a complement circuit 26, of an OR gate 27 of a bit shift circuit 28, of an AND gate circuit 29 and of a summing assembly 30 and multiplexer -register 31 similar to the set 23 and 22. The clock signal H is equal to 0 during a first half-period and to 1 during the following half-period (fig. 6). The signal M2 at the output of the OR gate circuit 27 consists of the content of the register M1 supplemented at 26 when H = 0 and during the following half-period, when H = 1, it is formed of a word of eight bits 1. The offset introduced by circuit 28 is a function of the value of the parameter m which can have eight different values from ^{M =} Go to m = G _o + G, G varying from 0 to 7. The inputs of circuit 28 have seven bits 0 and the eight-bit word M2 from circuit 27. This arrangement is such that the word M3 recovered at the output of circuit 28 represents the value θm for the value M considered when H = 1 and the product M1.θ for H = o. The number represented by M3 is forced to 0 when Δ _n-1 = 1 by the circuit gate AND 29, otherwise it is presented to the adder 30 whose incidental carry is worth 1. The initial value θ _o is introduced into the integrator register 31 and added or subtracted from the output M4 of the AND circuit 29 according to the sign of the parameter S of direction of the trace. The output of the summator 30 is looped back to the register 31 to produce the value P _n responding to the algorithm. The polar angle value P _n is transmitted downstream through a register circuit buffer 32.

The other circuits shown include waiting registers 33 and 34 in which the initial value θ _o and an image rotation value ϕ are written respectively. This value is added to the value θ _o by means of a summing circuit 35.

To perform a linear plot, that is to say to represent a vector by a succession of elementary vectors, the number M4 at the output of the gate circuit 29 is forced to 0 by the signal SV applied to the AND gate circuit 29 via of an OR gate circuit 37 which receives the signal Δ _n by its second input. Thus the output value Pn retains the initial value θ _o , or θ _o + ϕ in the case of an angle image rotation ϕ.

An important advantage of the invention is to allow the drawing at constant speed of the circles whatever their diameter in the total range of variation R _D to R _K , the ratio of the extreme radii being equal to ²⁸ in the example considered.

Le paramètre m se trouve doublé lorsque la vitesse est diminuée de moitié ce qui revient à diminuer de moitié l'angle 0 et disposer de vecteurs élémentaires plus petits pour conserver la même valeur de rayon sur l'écran.A speed change may be necessary, for example, because the number of symbols to be represented becomes very high, or else, as a result of a change of colors in the case of a color representation on a three-color tube. To satisfy this condition the parameter V of the speed is introduced into the exponent m to vary the speed in the ratio 2 each time and the range of the circles G is previously added to the speed in a summing circuit 36 which allows to compensate for the effect of the size of the elementary vector on the radius of the traced circle. Parameter 0 is thus of the form

The parameter m is doubled when the speed is halved which amounts to halving the angle 0 and having smaller elementary vectors to keep the same value of radius on the screen.

The circular arc tracing is obtained by checking the integration time in the integrator circuits 8 and 9 from the annex computer programmed accordingly.

The particular method implemented in a curve generating device according to the invention is characterized in that a quasi-continuous variation of the radius R desired for the circle to be displayed is obtained over a wide range of variation using a binary variation parameter 0 angle at the center, as well as possibly, a binary variation of the value U of the elementary vector combined with a binary variation of the speed V of the plot; the corresponding digital processing is carried out according to a relatively simple logic assembly, of small overall size and therefore particularly suitable for constituting airborne equipment and being integrated into an electronic piloting indicator system.

Claims (10)

1 - Curve generator device for viewing symbols on a cathode screen and in particular circular symbols, characterized in that it includes digital calculation means (1) developing a parameter ΔL defined by the relationships

where U is the predetermined value of an elementary vector, 0 a predetermined value of angle at the center of a regular polygon with side L = U + ΔL circumscribed in the circle, θ being of the form

, and logical operational processing circuits grouping together, a first summing circuit (2) resolving

with x ₀ predetermined between 0 and L, a circuit (3) developing the binary factor Δ _n equal to 1 for x _n greater than or equal to U, a multiplier circuit (4) solving

a second summing circuit (5) resolving

and a third summing circuit (6) delivering the value of polar angle P = θ _n - a of the plot formed of successive elementary vectors ending on the polygon of side L. 2 - Device according to claim 1, characterized in that the angle value at the center θ is determined by a parameter m according to the relation

where m = Go + G, Go being an integer and G a number varying between 0 and K to define a total range of variation of the radius R between R ₀ (m = Go) and R _K (m = Go + K) with

. 3 - Device according to claim 2, characterized in that the parameter m is of the form m = Go + G-V where V is an integer representing the speed of the plot. 4 - Device according to any one of claims 1 to 3, characterized in that the calculation means (1) deliver a binary factor S representative of the direction of the plot. 5 - Device according to any one of claims 1 to 4 characterized in that the transmission of the factor Δ _n from the generator circuit (3) takes place through an OR gate circuit (17-37) which receives by a second input of the calculation means a signal (SV) of value 1 in the case of a linear vector line and of value 0 in the case of a circle line. 6 - Device according to claim 4, characterized in that the processing circuits include a memory register (21) receiving the data ΔL, m and S, a first summing circuit (23) receiving ΔL from said register by a first input and connected by its second input and by its output respectively at the output and at a first input of a first multiplexer-register circuit (22), the latter comprising a second input receiving a predetermined initial value x _o (x _n for n = 1) and between 0 and L and having its output connected elsewhere through an OR gate circuit (27) to a bit shift circuit (28) receiving the data m, the OR gate circuit receiving a clock signal (H) by its second input, the offset circuit being connected to a second summing circuit (30) through an AND gate circuit (29) receiving A by a second input, the second summing receiving the data S representing the sign of the summing and being connected by another input to the output of a second multiplexer-register circuit (31) which receives by a pre first input of an initial polar angle data 0 of the trace and being connected by a second input to the output of the second summing circuit delivering the polar angle information P _n of the trace. 7 - Device according to all of claims 5 and 6, characterized in that the AND gate circuit (29) is connected by an inverted input to the output of an OR gate circuit (37) receiving by two inputs respectively the data Δ _n and SV. 8 - Device according to claim 3 and any one of claims 4 to 7, characterized in that it comprises a summing circuit (36) receiving on an input the data Go + G and V on a second input and delivering the parameter m at exit. 9 - Device according to any one of claims 6 to 8, characterized in that it comprises a register (33) receiving the initial data θ _o , a register (31) receiving a data ϕ of possible image rotation, a summing circuit (35) supplied by the outputs of these registers and the output of which is connected to the first input of the second multiplexer-register circuit (31). 10 - Device according to any one of claims 1 to 9, applied to the display of linear and circular symbols on a cathode screen, characterized in that the polar angle value P of the trace is transmitted through a buffer register circuit ( 32) to a memory circuit called sine-cosine table (7) which feeds integration circuits (8, 9), the integration time of which is controlled by an annex computer comprising said calculation means.

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