Method and device for producing a pulse trail

Information

  • Patent Grant
  • 6522289
  • Patent Number
    6,522,289
  • Date Filed
    Wednesday, June 20, 2001
    23 years ago
  • Date Issued
    Tuesday, February 18, 2003
    21 years ago
Abstract
The invention relates to a method for producing a pulse trail for at least one target whose actual position is represented in a continuous manner in a radar image of a radar device. In order to improve said method, wherein the pulse trails are represented on the radar screen in a highly visible manner for a viewer without any overcrowding of the radar screen when a plurality of targets that should be displayed simultaneously are present, the actual target position can be seen by means of a plurality of pixels that cover a continuous surface of the radar image and prior target positions are represented by a thinning out of said pixels that increases according to the chronological status of the respective target positions in the area.
Description




BACKGROUND OF THE INVENTION




The invention relates to a method and an apparatus for producing a persistence trail for at least one target whose respective current position is represented in a continuous manner in a radar image of a radar instrument.




Such persistence trails which are produced on the radar screen in a manner assigned to individual targets describe the tracks of located targets on the radar image, from which an observer can distinguish the movement behavior of the targets and also recognize collision risks evident from the directions of movement and eliminate them by suitable maneuvers instigated by said observer.




In a known method of this type (DE 29 24 176 C2), the radar echoes of the current panorama sample and of a plurality of preceding panorama samples, after storage in a single image memory, are displayed on the screen of the radar instrument. The image memory used is a read/write memory which is oriented in x,y coordinates and in which storage is performed by storing the intensities of the radar echoes currently received in each case in successive samples of the panorama, with the memory addresses corresponding to their spatial coordinates. The intensities obtained from previous samples are preserved in this case. The image content of the image memory is read out independently of the chronological order of reception of the radar echoes and represented on the radar image. As a result, the intensities stored for successive panorama samples appear strung together on the screen and describe the tracks or the persistence trails of the targets.




In a further configuration of the known method, the stored intensities are reduced by one or more increments after a predeterminable number of panorama samples, as a result of which the preceding target positions are represented on the screen with an intensity that decreases with age. The length of the persistence trails is thus dependent not only on the target speed but also on the speed with which a complete panorama sample is effected, and thus allows the time interval for which the persistence trail is represented to be assigned to the length of the persistence trail only in the case of a constant rotational speed of the radar antenna. If the rotational speed is changed, the time interval must be redefined.




BRIEF SUMMARY OF THE INVENTION




The invention is based on the object of improving a method of the type mentioned in the introduction to the effect that the persistence trails, with little outlay, appear in the radar image in a manner that is highly visible to the observer without overburdening the radar image in the case of a plurality of simultaneously represented targets.




The object is achieved according to the invention by means of the features in patent claim


1


.




The method according to the invention has the advantage that it can be carried out using standard graphics cards in a standard screen or video device and, as a result, can be implemented practically without any additional outlay. The persistence trails visible on the screen are very clear and do not overburden or overload the radar image even in the case of a multiplicity of targets appearing on the radar image, since, by virtue of the thinning out of pixels that increases with increasing age, their luminosity diminishes towards that end of the persistence trail which faces away from the current target position.




Expedient embodiments of the method according to the invention with advantageous developments and configurations of the invention emerge from the further claims.




The method according to the invention can be realized in a particularly advantageous manner in that, in accordance with a preferred embodiment of the method, the amplitudes of the radar echoes received by the radar instrument are stored in a radar video memory, whose memory cells are oriented in x,y coordinates, in that the memory content of the radar video memory is written as 1-bit information memory cell by memory cell to at least one trail memory, whose memory cells are oriented in x,y coordinates, in so far as the memory content of the individual memory cells exceeds a first predetermined value, in that the memory content of the trail memory is continuously erased according to an e.g. pseudo-random method for thinning out pixels, in that firstly the memory content of the trail memory is written to an image buffer memory, whose memory cells are oriented in x,y coordinates, and, chronologically succeeding that, the memory content of the radar video memory is written, in so far as the memory contents of the individual memory cells of the radar video memory exceed a second predetermined value, and in that the memory content of the image buffer memory is represented in a continuous manner on the radar screen—oriented in x,y coordinates—of the radar instrument as a pixel per memory cell.




Storing the persistence trails in a special trail memory not only enables the pixels to be thinned out in a particularly simple manner, but also enables, without difficulty, the changeover of the representation mode true-motion to the representation modes relative-motion and relative-motion true trails (center display), in which one's own location, that is to say one's own ship carrying the radar instrument, is fixed in the radar image, preferably in the center thereof, and vice versa, since only the memory content of the trail memory has to be cyclically shifted in accordance with the movement of one's own ship or the addressing of the memory cells of the trail memory has to be cyclically changed in accordance with the movement of one's own ship. If two trail memories are used, no loss of the persistence trails is associated with the changeover, with the result that, unlike in the case of known radar instruments, it is not necessary to accept a waiting time, which lasts at least a plurality of antenna rotations, until the persistence trails reappear on the radar image in the representation mode respectively chosen.




The provision of the additional memories having the same memory size has hardly any appreciable effect on the production costs of a screen device operating according to the method, since memory cards of the required size are extremely inexpensive. Furthermore, a color coding can be achieved in a simple manner using the trail memory, with the result that the persistence trails can also additionally be represented in different colors.











BRIEF DESCRIPTION OF THE FIGURES




The invention is described in more detail below using an exemplary embodiment illustrated in the drawing. In the figures, in a diagrammatic illustration in each case:





FIG. 1

shows a block diagram of a radar instrument according to an embodiment of the claimed invention,





FIG. 2

shows an enlarged illustration of the radar image that can be seen on the screen of the radar instrument in

FIG. 1

, and





FIG. 3

shows an illustration of the memory content of a trail memory in the radar instrument in accordance with

FIG. 1

at three successive instants.











DETAILED DESCRIPTION OF THE INVENTION




The radar instrument illustrated as a block diagram in

FIG. 1

has a rotating radar antenna


10


in a known manner, which antenna can be used to detect targets according to the principle of radio detection and ranging. Instead of mechanical rotation of the antenna


10


, the antenna can also be rotated electronically. Each radio detection and ranging signal, or radar echo, received by the antenna


10


is fed to the receiving device of a transmitting and receiving device


11


, is correspondingly conditioned there and converted into digital signals in an analog-to-digital converter


12


. The digital signals present in o,φ coordinates (distance and direction-finding) are transformed by a coordinate transformer


13


into an x,y coordinate system and fed to an image generator


14


, which represents the position of the targets identified by the radar echoes in a radar image


15


which appears on the radar screen


16


of a screen or video device


17


.




A radar image


15


for an arbitrarily chosen scenario is shown enlarged in FIG.


2


. The radar image


15


is illustrated in the “relative-motion mode”, i.e. the positions of the detected targets are represented in a reference system referring to one's own ship. Therefore, one's own ship, designated by


20


in

FIG. 2

, is always situated at a fixed point on the radar image


15


, in this case in the center of the radar image


15


. In the radar image


15


of

FIG. 2

, the radar instrument detects three different targets


21


to


23


, firstly the respective current position of the targets


21


to


23


being represented and, secondly, chronologically preceding target positions of the targets


21


to


23


in each case being represented as a persistence trail


24


identifying the chronological status, so that these persistence trails


24


can provide an overview of the positions of the targets


21


to


23


changing with time. The representation of the persistence trails


24


for the individual targets


21


to


23


is effected in such a way that the current target position of the targets


21


to


23


is made visible by a number of pixels covering a contiguous area in the radar image


15


and the chronologically preceding target positions are represented by a thinning out of pixels in the area, said thinning out increasing with the chronological status of the respective target position, so that the number of pixels activated within the area decreases as the age of the target position increases. This is illustrated in the radar image


15


of

FIG. 2

by the fact that the current target positions are in each case occupied by a black area which is increasingly interrupted in a dotted manner at the preceding older target positions. The older the represented target position, the larger the gaps in the closed area on account of the thinning out of pixels, thereby producing for the preceding target positions a dot pattern which becomes increasingly sparse as the age of the respective target position increases.




In order to produce the radar image


15


with the targets


21


to


23


and the persistence trails


24


assigned to each target


21


to


23


, the image generator


14


has a radar video memory


25


, a trail memory


26


, an image buffer memory


27


and a control unit


28


controlling the read-in and read-out processes of the memories


25


to


27


. The three memories


25


to


27


are each oriented in x,y coordinates and have an identical memory size with regard to the coordinate range. The radar video memory


25


is connected, on the input side, to the output of the coordinate transformer


13


and, on the output side, to a respective comparison circuit or a comparator


29


and


30


. The trail memory


26


is connected, on the input side, to the output of the first comparator


29


and, on the output side, via a second multiplexer


35


, whose function will be explained later, to one input of the multiplexer


31


, to whose other input the output of the second comparator


30


is connected. The memory input of the image buffer memory


27


is connected to the output of the multiplexer


31


and the memory output of the image buffer memory


27


is connected to the video device


17


. A first comparator threshold


32


is applied to the first comparator


29


and a second comparator threshold


33


is applied to the second comparator


30


, the second comparator threshold


33


preferably being made equal to zero. The first comparator


29


is designed in such a way that a 1-bit information item is present at its output if a value present at its input, in this case the memory value of the radar video memory


25


, exceeds the first comparator threshold


32


. The second comparator


30


is designed in such a way that a value present at its input, in this case the memory value of the radar video memory


25


, is present at its output connected to the multiplexer


31


if said value is greater than the second comparator threshold


33


. The multiplexer


31


, which is controlled by the control unit


28


and has merely the function of a data selector, switches its output periodically and in a chronologically successive manner firstly to its input connected to the trail memory


26


and then to its input connected to the radar video memory


25


.




The image generator


14


constructed in this way operates according to the following method:




The amplitudes of the electrical reception signals of the transmitting and receiving device


11


, the “video signals or video data”, which represent the radar echoes received by the antenna


10


and have been digitized and subjected to signal conditioning, are stored in accordance with their associated x,y coordinates in the correspondingly addressed memory cells of the radar video memory


25


. The memory content of the radar video memory


25


is read out cyclically and written as 1-bit information by the first comparator


29


memory cell by memory cell to the trail memory


26


, if the memory content of the individual memory cell exceeds the first comparator threshold


32


. As a result, all the memory cells of the radar video memory


25


in which the stored amplitude is greater than the first comparator threshold are cyclically copied as 1-bit information to the trail memory


26


. For a color representation of the persistence trails on the radar image


15


, during the writing process the 1-bit information is additionally coded in such a way that its coding can be clearly distinguished from the coding of the memory content of the radar video memory


25


. During the copying or writing operation, the content of the trail memory


26


is not erased but only overwritten. If the amplitude in a memory cell of the radar video memory


25


is less than the first comparator threshold


32


, then there is no occupancy of the identically addressed memory cell in the trail memory


26


. The memory content of the memory cells of the trail memory


26


is continually erased by a method for thinning out pixels, e.g. a pseudo-random method. In this case, the erasure frequency is independent of the frequency of writing to the trail memory


26


, in which case, by altering the erasure frequency, the length of the persistence trail produced can be chosen independent of the rotational speed of the radar antenna.





FIG. 3

illustrates the construction of such a persistence trail


24


in three phases.

FIG. 3



a


shows the trail after the initiation phase as copied from the radar video memory


25


. In

FIG. 3



b


, the target has moved on somewhat. The trail image at the current position is still closed, while the trail image at the position from the initiation phase has been thinned out by approximately 20% by the erasure method employed. In

FIG. 3



c


, the target has once again moved on somewhat, so that now three regions can be discerned. The trail is closed in the front region of the trail, that is to say the direct, current target position. The memory content is thinned out by approximately 20% in the middle region of the trail and by approximately 40% in the rear region.




The memory contents of trail memory


26


and radar video memory


25


are copied into the image buffer memory


27


cyclically and chronologically successively in the order mentioned, the second comparator


30


performing sorting such that the memory content of the radar video memory


25


is written, and if appropriate overwrites pixels previously written from the trail memory


26


, only if the memory contents of the individual memory cells of the radar video memory


25


exceed the second predetermined value. In this case, the multiplexer


31


controlled by the control unit


28


connects the respective output of trail memory


26


and radar video memory


25


to the memory input of the image buffer memory


27


in a chronologically correct manner. The memory content now copied in this way into the image buffer memory


27


is a mapping of the radar image


15


which is to be presently represented on the radar screen


16


and is cyclically renewed and is represented in a continuous manner on the radar screen


16


.




The multiplexer


31


can be dispensed with and the outputs of trail memory


26


and comparator


30


can be connected directly to the memory input of the image buffer memory


27


if a corresponding control routine is provided in the control unit


28


, which control routine effects the read-out of trail memory


26


and radar video memory


25


in the manner described above.




As already mentioned, the image representation is effected in relative motion. If it is to be performed in relative-motion true trails, then the content of the trail memory


26


has to be cyclically shifted or a readdressing of the memory cells of the trail memory


26


has to be performed, said readdressing compensating the intrinsic movement of the ship carrying the radar instrument.




In order, in the event of changeover between the representation modes, which can be performed arbitrarily by the operator, to avoid the loss of the persistence trails, which are built up again after a changeover operation only after a relatively long time lasting a plurality of antenna revolutions, a second trail memory


34


is provided, whose memory input is likewise connected to the output of the first comparator


29


. As a result, the 1-bit information items are simultaneously copied into both trail memories


36


,


34


, in which case, however, when the 1-bit information items are written to the second trail memory


36


, the control unit


28


carries out a readdressing of the memory cells, said readdressing being important for the true-motion representation, in such a way that the movement of one's own ship is spatially compensated in the x,y coordinate system. As a result, the trail is built up in relative motion in the first trail memory


26


and in true motion in the second trail memory


34


, to be precise at the same time. The second trail memory


34


is processed in parallel by the control unit


28


in the same way, so that its memory content is continuously erased routinely according to the same method and the above-described thinning out of pixels is effected in the memory content representing the persistence trails


24


. In the event of a changeover of the representation mode on the radar screen


16


, it is now optionally possible to have recourse to the first trail memory


26


and to the second trail memory


34


, and the persistence trails


24


can thus be represented in relative motion or true motion on the radar screen


16


.




For optional access to the two memory outputs of the trail memories


26


and


34


, the latter are connected to the two inputs of a second multiplexer


35


, whose output is connected to one input of the first multiplexer


31


. The second multiplexer


35


is controlled by means of a changeover switch


36


that can be operated manually. In this case, if the changeover switch


36


assumes the switching position indicated diagrammatically in

FIG. 1

, then in the multiplexer


35


, the output thereof is connected to the input connected to the first trail memory


26


. If the changeover switch


36


is closed, then the output of the multiplexer


35


is connected to the input connected to the second trail memory


34


.



Claims
  • 1. A method for producing a persistence trail for at least one target having a current target position and one or more previous target positions, wherein the current target position is represented in a continuous manner in a radar image of a radar instrument, and the current target position is made visible by a number of pixels covering a contiguous area in the radar image, and wherein the previous target positions are represented by a thinning out of pixels in the radar image, the thinning out increasing with increasing age of the respective target position, the method comprising:(a) storing amplitudes of radar echoes received by the radar instrument in a radar video memory; (b) writing the content of the radar video memory as a 1-bit item of information to at least one trail memory; and, (c) erasing the trail memory by a method for thinning out pixels in a chronologically successive manner when the content of individual trail memory cells exceeds a first predetermined value, comprising: (i) writing the content of the trail memory to an image buffer memory, and subsequently (ii) writing the content of the radar video memory to the image buffer memory when the contents of individual memory cells of the radar video memory exceed a second predetermined value; wherein the radar video memory, trail memory, and image buffer memory all have memory cells which are oriented in x,y coordinates, and wherein the image buffer memory is represented in a continuous manner on the radar image as a pixel per memory cell.
  • 2. The method as claimed in claim 1, wherein the second predetermined value is set to zero.
  • 3. The method as claimed in claim 1, wherein the trail memory has a read-in and a read-out frequency and is erased at a frequency that is independent of the read-in/out frequency of the trail memory.
  • 4. The method as claimed in claim 1, wherein the 1-bit item of information is coded differently from the coding of the radar video memory.
  • 5. The method as claimed in claim 4, wherein coding of the 1-bit item of information is carried out during the process of writing to the trail memory.
  • 6. The method as claimed in claim 1, wherein the 1-bit item of information is written simultaneously to two trail memories.
  • 7. The method according to claim 1, wherein the pixels are thinned out by a pseudo-random method.
  • 8. The method according to claim 1, further comprising readdressing the memory cells in the x,y coordinate system to compensate for any movement of the radar instrument when the 1-bit item of information is written to or read from one trail memory.
  • 9. The method according to claim 8, wherein the content of one trail memory is written to the image buffer memory.
  • 10. An apparatus for producing a persistence trail for at least one target having a current target position and one or more previous target positions, wherein the current target position is represented in a continuous manner in a radar image of a radar instrument, and the current target position is made visible by a number of pixels covering a continuous area in the radar image, and wherein the previous target positions are represented by a thinning out of pixels in the radar image, the tinning out increasing with increasing age of the respective target position, the apparatus comprising:(a) a radar video memory which is connected to a receiving device of the radar instrument, and stores amplitudes of radar echoes obtained from the receiving device; (b) at cast one trail memory; (c) an image buffer memory having an input connected to an output of the trial memory, wherein the radar video memory, trail memory, and image buffer memory all have inputs and outputs which are oriented in x,y coordinates and have the same memory size in the x,y coordinate range; (d) two comparators having inputs and outputs, wherein: (i) the inputs are connected to the output of the radar video memory, and the output of the first comparator is connected to the input of the trail memory, and the first comparator outputs a 1-bit item of information when an input value exceeds a first comparator threshold; and (ii) the output of the second comparator is connected to the input of the image buffer memory, and when an input value exceeds a second comparator threshold, the second comparator switches the input value to its output; and (e) a control unit for controlling and updating the radar video memory, trail memory, and image buffer memory, wherein the control unit: (i) continuously erases the content of the trail memory by a method for thinning out pixels, and (ii) controls the read-in and read-out processes of the memories, wherein the content of the trail memory and then the content of the radar video memory are read into the image buffer memory.
  • 11. The apparatus as claimed in claim 10, comprising two trail memories having inputs connected to the output of the first comparator, whereinthe control unit controls the operations of: (i) writing the 1-bit information item present at the output of the first comparator to one trail memory, and (ii) reading the stored 1-bit item of information from one trail memory, in order to readdress the memory cells in the x,y coordinate system and thereby compensate for any movement of the radar instrument; and the input of the image buffer memory is connected to one of the two trail memories.
  • 12. The apparatus as claimed in claim 11, wherein the connection of the image buffer memory to the trail memories is initiated manually.
  • 13. The apparatus according to claim 10, wherein the pixels are thinned out by a pseudo-random method.
Priority Claims (1)
Number Date Country Kind
198 44 620 Sep 1998 DE
PCT Information
Filing Document Filing Date Country Kind
PCT/EP99/01475 WO 00
Publishing Document Publishing Date Country Kind
WO00/19232 4/6/2000 WO A
US Referenced Citations (9)
Number Name Date Kind
3697986 Colby Oct 1972 A
3742494 Embling et al. Jun 1973 A
3803596 Embling Apr 1974 A
3882502 Peabody et al. May 1975 A
4162494 Bacon Jul 1979 A
4208657 Bryden et al. Jun 1980 A
4580164 Andrieu et al. Apr 1986 A
4829308 Tol et al. May 1989 A
5459472 Giraudy Oct 1995 A
Foreign Referenced Citations (1)
Number Date Country
2924176 Dec 1980 DE