GB2194113A - Azimuth recognition system - Google Patents

Abstract

In a polar-cartesian scan converter, the azimuthal co-ordinate may be specified in any of a number of forms. The converter is able to digitize any of these forms, and, if it is supplied in a coarse form, to interpolate. A plurality of scans from different sources, with azimuthal co-ordinates in different forms, may be displayed simultaneously. <IMAGE>

Description

SPECIFICATION Azimuth recognition system The present invention relates to an azimuth recognition system well suited for use with a radar system or the like so that the pictures generated from a plurality of different polar coordinate display apparatus to present the azimuth in different formats or forms are selectively displayed by a single rectangular coordinate display apparatus.

Such conversion display apparatus for converting a polar coordinate display to a rectangular coordinate display has been used with a radar or the like.

Then, the form of an azimuth signal generated from an antenna of a radar or the like differs with different types of radars, that is, it takes the form of an output signal of a synchro, an output signal of a resolver or a pulse signal of a shaft encoder which has recently come into use owing to its low cost.

Particularly in the case of remote display, the conversion display apparatus should preferably be adapted to be connected to many different types of radar systems. In the past, however, it has been necessary so that each time the form of a radar azimuth signal changes the converting device must be replaced with one which suits the new form and therefore many different types of converting devices must be used in correspondence to the different forms of azimuth signals.

Also, in the past, an S/D converter or R/D converter has been used for the purpose of digitizing the output of an analog angle transducer, such as, a synchro signal or resolver signal in view of its capacity to select a wide range of input signals and its accuracy and reliability.

On the other hand, in the case of a pulse-type azimuth signal, a counter for counting pulse signals inputted as the azimuth signal has been used.

However, even if these converting devices are used, there still exists the need to make uniform the angular unit per bit for every azimuth signal in the scanning conversion unit.

For instance, the previously mentioned S/D and R/D converters heretofore used have been usually of the 12-bit binary type and the minimum unit corresponds to 0.0878 degrees. In the case of the pulse-type lazimuth signal, however, there are different numbers of pulses per radar rotation, e.g., 360, 45(t 1080 and 1024 and each pulse corresponds to 1 degree, 0.8 degrees and 0.35 degrees when one radar rotation is represented in terms of 360 pulses, 450 pulses and 1024 pulses, respectively.

Also, if, for example, one radar rotation is given in terms of 360 pulses in the case of the pulse-type azimuth signal, each pulse corresponds to 1 degree and using this alone as such as the azimuth data greatly deteriorates the accuracy of coordinate conversion.

Then, to attain an improvement in this angular accuracy circuit-wise has the disadvantages of requiring complicated logics and altering the logics in response to a change in the rotational angle per pulse.

The present invention has been made in view of these circumstances and it is an object of the invention to provide an azimuth recognition system well suited for use with an apparatus so designed that each of a plurality of pictures in the form of polar coordinate displays generated according to azimuth signals having different display forms is displayed in the form of a single rectangular coordinate form.

In accordance with the invention, noting the fact that computing means (CPU) is used in the modern radar systems, anticollision apparatus aid (ARPA) or the like, the computing means is utilized to obtain single-form rectangular coordinate data for rectangular coordinate display purposes.

A feature of this invention resides in the provision of form pointing means for pointing the form of azimuth data, data interpolating means whereby during data conversion data is interporated in accordance with the form of the azimuth data to obtain interpolated azimuth data, and data converting means for performing data conversion in accordance with the form pointed by the form pointing means to obtain rectangular coordinate data from the azimuth data and the interpolated azimuth data.

The form of polar coordinate display azimuth data to be converted is pointed by the form pointing means.

The data interpolating means interpolates azimuth data in accordance with the input azimuth data. The azimuth data to be interpolated is one having an angle other than that of the input azimuth data.

The desired single-form rectangular coordinate data is obtained by the data converting means by using the input azimuth data and the interpolated azimuth data.

In accordance with the invention, even if azimuth data have many different forms, each of the azimuth data is converted to standardized azimuth data and the interpolation of azimuth data is effected as occasion demands, thereby producing the following effects.

(1) When the apparatus is connected to any of radars which are different in azimuth data form from one another, the requirements can be met easily without modifying its circuit construction.

(2) Even if the accuracy of azimuth data is lower than the display capacity of the rectangular coordinate-type display apparatus, it is possible to prevent any considerable reduction in the display capacity of the apparatus by performing the interpolation.

(3) The selective connection to different types of radars which has heretofore been considered to be complicate and difficult can be easily selected and performed.

The above and other objects as well as advantageous features of the invention will become more clear from the following description taken in conjunction with the drawings, in which: Fig. 1 is a block diagram showing an embodiment of the invention; Fig. 2 is a block diagram showing a conventional apparatus; Fig. 3 is a block diagram showing an example of the pulse count type; Fig. 4 is a time chart useful for explaining the interpolation of data; Fig. 5 is a flow chart showing the interpolation procedure; Fig. 6 is a block diagram showing another embodiment of the invention.

Before describing preferred embodiments of the invention, an example of the ordinary conventional conversion display apparatus will be described with reference to Fig. 2.

Fig. 2 shows a known type of conversion display apparatus for converting a polar coordinate display to a rectangular coordinate display. The illustrated apparatus is used with a radar system by way of example.

In the Figure, an antenna 50 is connected to an A/D converter 52 where an azimuth signal corresponding to the pointing direction of the antenna is converted to a digital signal.

Then, the A/D converter 52 is connected to- a sine-cosine converter 56 in a scanning conversion unit 54 and the sine-cosine converter 56 is connected to a coordinate converter 58.

By virtue of the scanning conversion unit 54 comprising the sine-cosine converter 56 and the coordinate converter 58, coordinate data for rectangular coordinate display is computed from the digitized azimuth signal or the coordinate signal for polar coordinate display.

The coordinate converter 58 is connected to a video memory 60 so that the output data indicative of the coordinates converted by the coordinate converter 58 is applied as address datato the video memory 60. Then, the video memory 60 is connected to a CRT display 62 for producing a rectangular coordinate display.

On the other hand, a receiver-transmitter 64 is connected to the antenn:a 50 so that a radio wave based on a trigger signal produced in the transmitter-receiver 64 is radiated from the antenna 50 and the reflected radio wave from an object to be measured is received by the transmitter-receiver 64, thereby generating the resulting video signal of the object as well as a trigger signal. The trigger signal is applied to a clock circuit 66 and the video signal is applied to an A/D converter 68.

The clock circuit 66 is connected to the coordinate converter 58 of the scanning conversion unit 54 and clock signals generated in response to the trigger signal are applied to the coordinate converter 58.

The A/D converter 68 is connected to the video memory 60 through a buffer memory 70.

The buffer memory 70 is designed so that a video signal for one sweep corresponding to each trigger signal, for example, is temporarily stored in the buffer memory 70 in a real-time manner with the signal reception of the transmitter-receiver 64 and the video signal is read and delivered to the video memory 60 at a predetermined timing.

A synchronizing circuit 72 is connected to the video memory 60 and the CRT display 62, respectively, so that the synchronizing circuit 72 applies an address signal for reading the stored video signal to the video memory 60 and also applies a synchronizing signal to the CRT display 62. The address signal is delivered in correspondence with the delivery of the synchronizing signal so that a rectangular coordinate display is made on the CRT display 62 in accordance with the video signal stored in the video memory 60.

The operation of this apparatus will mow be described. Generally, a picture on a radar or the like is displayed by the polar coordinates, by the azimuth angle and the distance from the point of transmission. On the contrary, the CRT display 60 makes rectangular coordinate displays.

Therefore, the display position of the video signal is subjected to coordinate conversion by the scanning conversion unit 54.

The azimuth sinal indicating the azimuth angular position of the antenna 50 is converted to a digital signal by the A/D converter 52 and then applied to the sine-cosine converter 56 which in turn determines the sine and cosine values of the angle in question.

Then, in accordance with these values, the rectangular coordinate values of a video signal sampling point at this angle are determined by the coordinate converter 58. At this time, the distance of the sampling point from the polar coordinate center is provided by the output signals of the clock circuit 66.

The rectangular coordinate values determined in this way by the coordinate converter 58 are applied, as write address to the video memory 60.

On the other hand, the video signal at these coordinates is converted to a digital signal by the A/D converter 68, temporarily stored in the buffer memory 70 and then applied to the video memory 60. At this time, the clock circuit 66 generates its signals in such a manner that the operation timing of the A/D converter 68 corresponds to the operation timing of the coordinate converter 58. By virtue of this operation, the video signal of the corresponding rectangular coordinate values is stored in one of the addresses of the video memory 60.

Then, the video signals stored in the video memory 60 are read at a high speed by the read address singals generated from the synchronizing circuit 72 in synchronism with the scanning of the CRT display 62 and the video signals are applied to the CRT display 62, thereby making a high brightness display in rectangular coordinate form.

Referring to Fig. 3, there is illustrated an ordinary digital azimuth singal generator of the pulse counter type. In the Figure, a counter 74 is reset or cleared by a reference signal of zero azimuth angle to count up in response to the application of the subsequent pulses. The resulting count value is outputted as azimuth angle data.

Fig. 1 shows an embodiment of the present invention. In the Figure, an A/D converter 10 for receiving an azimuth signal is connected to a buffer circuit 12 so that the azimuth signal is changed to a digital form and temporarily stored in the buffer circuit 12.

The A/D converter 10 includes an S/D converter, R/D converter, pulse counter, etc., and thus any one of the S/D converter, R/D converter and the pulse counter is selected in accordance with the form of the radar azimuth signal to be displayed.

The buffer circuit 12 is connected to a data bus 16 for a CPU 14 which is designed so that when an interrupt signal such as a transmission trigger signal is applied, the unprocessed azimuth data is read from the buffer circuit 12 into the CPU 14.

Also, a setting adjusting switch 18 is connected to the data bus 16 of the CPU 14 and the setting adjusting switch 18 points the form of the unprocessed azimuth data.

In addition, a processing table 20 is connected to the data bus 16 as occasion demands and it is used for performing the azimuth data processing.

The processed standard azimuth data is temporarily stored in a latch circuit 22 connected to the data bus 16 and applied to a scanning converter 24. The scanning converter 24 corresponds to the scanning conversion unit 54 of Fig. 2 and performs the similar functions.

The operation of this embodiment will now be described. In this embodiment, various unprocessed azimuth data are each subjected to the following processing to obtain standard azimuth data. Then, the standard azimuth data is converted to obtain position data for rectangular coordinate display purposes or rectangular coordinate data corresponding to the address data for the video memory 60.

Firstly, the method of standardizing the form of azimuth data will be described.

Generally, the output of the S/D converter or R/D converter is of the 10-bit or 12-bit pure binary type. Assuming that the output is 12 bits long and its MSB represents 180 , there results 3601212 = 0.0878 , that is, 0.0878 per bit of LSB.

Also, in the case of the pulse type, particularly in the case of 1024 or 2048 pulses per rotation type, it is possible to raise 2 to a given power to obtain azimuth data and thereby handle it in the like manner as the 212 type data. Also, in the case of other types than the 2's involution type, such as, 360 or 450 pulses per rotation type, if N represents the number of pulses per rotation and D(degrees) represents the azimuth when the pulse count is M, then the following holds D = (360/N) x M (1) On the other hand, if the azimuth D is given by the 2'2 type, the following holds 360 D = 4096 x d (2) Since d represents the count obtained in the case of 4096 pulses per rotation, the count M can used as the azimuth data d of the 2'2 type if the following conversion is performed 4096 D = N x M (3) Next, the interpolation of azimuth data will be described. In the case of a radar, the transmitting purse repetition rate is 500 to 4000 pps and the antenna is generally rotated smoothly at 24 rpm or about 2.5 seconds per rotation. Even in the case of the lowest transmitting pulse repetition rate of 500 pps, the azimuth accuracy of video data is given as 360 . 1250 = 0.288 (4) However, where the number of pulses generated for every rotation of the antenna is 360 or 450, the azimuth accuracy becomes 1 or 0.8 and the azimuth interval is increased. Thus, the display accuracy is not necessarily satisfactory.

The azimuth corresponding to each trigger signal during the interval between the azimuths determined by the pulses is established and interpolated and the video data present during the interval are utilized effctively.

Next, this interpolation of azimuth data will be described in detail with reference to Figs. 4 and 5.

Fig. 4 shows a time chart for the interpolation in the case where the azimuth data requires 360 pulses per antenna rotation and the necessary standard azimuth data for coordinate conversion requires 500 Hz, and Fig. 5 is a flow chart showing the computing procedure for interpolation.

If one rotation of the antenna requires about 2.5 seconds, about three trigger pulses are applied to the CPU 14 during one pulse period of the azimuth data (See Fig. 4,(A) and (C)).

In this example, the A/D converter 10 is composed of a counter which counts up each time an azimuth data pulse of Fig. 4(A) is applied (See Fig. 4(B)).

In this case, if no interpolation is effected so that only count values M1 and M2 for example, are used as such as azimuth data, the azimuth values of video signals V1, V2, etc., (See Fig.

4(D)) at times T1, T2, etc., (See Fig. 4(C)) in the Figure become ths same as that indicated by the count value M1 and they are handled as the video data of the same azimuth position despite the fact that they are in fact video data of different azimuths.

Thus, the conversion expression of equation (3) is replaced as follows 4096 xrn (5) n n=Nxk (6) 'n=kxm+i (7) Here, k is a multiplier indicating the number of transmitting trigger pulses present in the interval between the azimuth data pulses. In the case of Fig. 4, k = 3 (See Fig. 4,(A) and (C)).

Then, when the count data M changes first as shown in the flow chart of Fig. 5, i = 0 is set and a new count data M is adopted (See steps SA and SB of Fig. 5). For instant, the count data changes from M1 to M2 at a time T4 so that the count data M2 is adopted (See Fig. 4(B)).

If there is no change in the count data M, the preceding value of m is incremented by 1 to advance the azimuth data in a pseudo manner (See step SC of Fig. 5).

By virtue of the foregoing operation, the azimuth accuracy of essentially 360 pulses is enhanced to one corresponding to 1080 pulses or about three times the essential accuracy.

Regarding other numbers of pulses, it is only necessary to arrange so that the values of n and multiplier k for m are suitably selected by the setting adjuster 18.

The azimuth data thus changed in form and subjected to the necessary interpolation by the CPU 14 in the above-mentioned manner or the standard azimuth data is applied to the scanning converter 24 through the latch circuit 22. Then, the sine and cosine values of the azimuth are obtained by the scanning converter 24 by calculation or by reference to the processing table 20 and hence rectangular coordinate values are determined.

Another embodiment of the invention will now be described with reference to Fig. 6.

This embodiment differs from the embodiment of Fig. 1 in that the section including the A/D converter 10 and the buffer circuit 12 is replaced by A/D converters 30 and 32 and a selector 34.

In Fig. 6, azimuth data of a first form is applied to the A/D converter 30 and azimuth data of a second form is applied to the A/D converter 32.

The A/D converters 30 and 32 are connected to the selector 34 and either of the azimuth data is delivered to the data bus 16 in response to a command from the CPU 14.

Also, a selector switch 36 is provided for the CPU 14 and the selection by the selector 34 is commanded by the operation of the selector switch 36.

With this embodiment, when azimuth data of different forms are inputted, the azimuth data are selectively processed through the selection by the selector 34 in response to the operation of the selector switch 36 and are all subjected to rectangular coordinate display.

In addition, when occasion demands, it is only necessary to connect third, fourth, --- --- converters so that suitable one of the input azimuth data is selected in accordance with their forms.

In addition, the present invention is applicable to a case where a plurality of pictures of polar coordinate displays based on azimuth data of different forms are simultaneously presented as rectangular coordinate displays by a single apparatus.

Claims (3)

1. An azimuth recognition system for obtaining singleform rectangular coordinate data for rectangular coordinate display from any one of a- plurality of azimuth data of different forms for polar coordinate display, said system comprising: form pointing means for pointing the form of said azimuth data; data interpolating means whereby during data conversion data is interpolated in accordance with the form of said azimuth data to obtain interpolated data; and data conversion means for performing data conversion in accordance with said form pointed by said form pointing means to obtain said rectangular coordinate data from said azimuth data and said interpolated azimuth data.

2. A system according to claim 1, wherein said data interpolating means includes means for changing a per-bit angular unit of said azimuth data in accordance with the pointing of said form pointing means.

3. An azimuth recognition system substantially as hereinbefore described with reference to, and as shown in, Figures 1 or 6 of the accompanying drawings.