Real time digital scan converter

• US 4,214,269 A
• Filed: 03/09/1979
• Issued: 07/22/1980
• Est. Priority Date: 03/09/1979
• Status: Expired due to Term

• Current Assignee: Advanced Technology Materials, Inc. (Entegris Incorporated)
• Original Assignee: Advanced Technology Materials, Inc. (Entegris Incorporated)
• Inventors: Parker, Edward J., Behlen, James C. Jr.
• Primary Examiner(s): Britton, Howard W.
• Application Number:
  US06/019,321
• Time in Patent Office: 501 Days
• Field of Search: 358/140, 343/5 SC, 343/5 DP, 343/6 TV
• US Class Current: 348/442
• CPC Class Codes: G01S 7/298 Scan converters
• CPC Class Codes: G01S 7/531 Scan converters

Abstract

A digital scan converter is disclosed for processing the sequence of analog signals supplied by a sector scanning surveillance system to form a signal compatible with television type display devices. The signals supplied by the surveillance system are digitized by an analog-to-digital converter at a rate proportional to the cosine of the azimuthal scan angle that is associated with each analog signal to thereby effect a first portion of the required conversion from the polar coordinate format of the surveillance system to the Cartesian coordinate format of the television display. The digitized signals are stored in a memory so as to permit addressing of a set of stored data that corresponds to one horizontal trace of the television display. The data sets corresponding to successive horizontal lines of the television display are sequentially accessed in accordance with conventional television timing signals and data is serially read from memory and supplied to a digital-to-analog converter at a rate that completes the required polar-to-Cartesian format conversion.

Claims

1. A digital scan converter for use with a scanning system which applies a sequence of n video return signals having a one-to-one correspondence with n radially extending scan lines that are angularly spaced apart from one another about the azimuthal axis of a polar coordinate system to define a sectorial surveillance region, each of said video return signals representing signal reflection occurring along said corresponding scan line, said digital scan converter for supplying signal information representative of at least a portion of said sectorial surveillance region relative to a Cartesian coordinate system wherein the first axis thereof is substantially parallel to said azimuthal axis of said polar coordinate system and the second axis of said Cartesian coordinate system is perpendicular to the first axis thereof, said digital scan converter comprising:

signal sampling means connected for receiving said sequence of n analog signals, said signal sampling means including means for digitizing each of said analog signals at a rate proportional to the cosine of the angle between said corresponding scan line and said azimuthal axis of said polar coordinate system to supply n ordered sets of data values, the successive data values of each said ordered set of data values representing signal reflection occurring from incremental regions of said surveillance region that are located along said corresponding scan line at equally spaced apart positions relative to said first axis of said Cartesian coordinate system;

memory means connected for receiving and storing said n ordered sets of data values, said memory means being addressable for accessing those ones of said data values that correspond to incremental regions of said surveillance region that are equally spaced apart from said second axis of said Cartesian coordinate system by a predetermined distance as an ordered set of data values in which successive data values are associated with the successive analog signals supplied by said surveillance system; and

memory control means connected to said memory means for sequentially accessing said sets of data values corresponding to said equally spaced apart incremental regions in order of increasing distance from said second coordinate axis of said Cartesian coordinate system, said memory control means including means for reading said sets of accessed data values at a rate proportional to the distance between said corresponding incremental regions of said surveillance region and said second coordinate axis of said Cartesian coordinate system to supply said signal information relative to said Cartesian coordinate system.

2. The digital scan converter of claim 1 wherein said memory control means further includes means for modulating the rate at which each of said sets of accessed data values are read as a function of the angle between the scan line corresponding to said associated analog signal and said azimuthal axis of said polar coordinate system.

3. The digital scan converter of claims 1 or 2 wherein said signal sampling means further includes means for supplying the first data value of each of said n sets of data values at the time at which each of said first data values corresponds to an incremental region of said surveillance region that is located a predetermined distance from said second axis of said Cartesian coordinate system.

4. The digital scan converter of claim 3 wherein said memory control means further includes timing means responsive to periodic synchronization pulses of an applied signal for reading a single set of said accessed data values in response to each of said synchronization pulses.

5. The digital scan converter of claim 4 wherein said memory control means further includes means for establishing the time at which the first data value of each of said accessed sets of data values is read relative to the time at which said synchronization pulse occurs and means for varying the time elapsing between the occurrence of said synchronization pulse and the reading of said first data value as a function of said distance between said corresponding incremental region of said surveillance region and said second axis of said Cartesian coordinate system.

6. The digital scan converter of claim 5 further comprising digital-to-analog converter means connected for receiving said data values read by said memory control means to supply said signal information relative to said Cartesian coordinate system as an analog signal.

7. A digital scan converter for supplying an analog signal representing signal information that is supplied by a scanning system of the type wherein said scanning system provides a sequence of discrete analog signals that are associated with a plurality of radially extending scan lines which are angularly spaced apart from one another and referenced to a polar coordinate system, said digital scan converter comprising:

signal sampling means connected for receiving said sequence of analog signals, said signal sampling means including means for digitizing each of said analog signals at a rate that is determined by the pulse repetition rate of an applied first clock signal to supply an ordered set of digitally encoded signals representative of each of said analog signals;

first signal generating means for supplying said first clock signal to said signal sampling means, said first signal generating means including means for supplying said first clock signal at a pulse repetition rate proportional to the cosine of the azimuthal angle of the scan line associated with the analog signal currently being supplied to said signal sampling means by said scanning system;

memory means connected for receiving said ordered sets of digitally encoded signals supplied by said signal sampling means, said memory means for storing values representative of each digitally encoded signal of said sequences of digitally encoded signals, said memory means being addressable to partition said memory means as a rectangular array of storage locations having a predetermined number of columns and a predetermined number of rows;

memory control means operably interconnected with said memory means and said signal sampling means for loading values corresponding to successive sets of digitally encoded signals into successive column locations of said rectangular array of storage locations with values corresponding to each particular ordered set of digitally encoded words being located into the successive row locations of a single column of said rectangular array of storage locations, said memory control means further including means for sequentially accessing said memory means on a row-by-row basis relative to said rectangular array of storage locations;

data means for reading the values stored as rows of said rectangular memory array to form a sequence of digitally encoded signals representative of each row of said stored values, said data means for reading said values being responsive to an applied second clock signal and including means for sequentially reading the values within a particular row of said rectangular memory array at a rate determined by the pulse repetition rate of said second clock signal;

second signal generating means for supplying said second clock signal, said second signal generating means including means for varying said pulse repetition rate of said second clock signal on a row-by-row basis relative to said memory array of said memory means to decrease said pulse repetition rate as each successive row of stored values is read from said memory means; and

digital-to-analog signal conversion means connected for receiving said sequence of digitally encoded signals representative of each of said rows of stored values, said digital-to-analog signal conversion means for supplying said analog output signal representative of said signal information.

8. The digital scan converter of claim 7 further comprising modulation means for varying the pulse repetition rate of said second clock means during each time interval in which the values within one of said rows of stored values are read from said memory means, said modulation means including means for increasing and decreasing said pulse repetition rate of said second clock signal as a function of the column location of the value currently being read.

9. The digital scan converter of claim 8 wherein said modulation means includes means for varying said pulse repetition rate of said second clock signal in accordance with the tangent of the azimuthal angle of the scan line that is associated with the analog signal that corresponds to the column location of the particular value being read.

10. The digital scan converter of claims 7, 8 or 9 wherein said second signal generating means further includes means for starting said second clock signal at a predetermined time that is functionally related to the row location of the row of data values currently being read.

11. The digital scan converter of claim 10 wherein said first signal generating means further includes means for selectively coupling said first clock signal to said sampling means after a predetermined number of clock pulses have been supplied by said first signal generating means and means for interrupting the flow of said first clock signal to said signal sampling means a predetermined time after said surveillance system begins to supply each of said discrete analog signals to said signal sampling means.

12. A digital scan converter for use with a surveillance system of the type which sequentially emits pulses of energy along a series of n radially extending scan lines that collectively define a sectorial surveillance system, with said scan lines being angularly spaced apart from one another relative to the azimuthal axis of an associated polar coordinate system to supply a sequence of n analog signals having a one-to-one correspondence with said n scan lines with each of said n analog signals representing signal reflection occurring along said corresponding scan line, said digital scan converter for supplying a video information signal representative of a predetermined portion of said sectorial surveillance region for driving a display device which operates on the basis of a Cartesian coordinate system, said video information signal causing said display device to display said predetermined portion of said surveillance region in an orientation wherein said azimuthal axis of said polar coordinate system associated with said scanning system is substantially parallel to the first axis of said Cartesian coordinate system that is associated with said display device, said video information signal including consecutive signal intervals corresponding to m lines of image display that are spaced apart from one another and substantially parallel to the second axis of said Cartesian coordinate system of said display device, said digital signal converter comprising:

an analog-to-digital converter circuit connected for receiving each of said n analog signals supplied by said surveillance system, said analog-to-digital converter being responsive to an applied first clock signal for supplying a series of digital signal values representative of signal reflection occurring from equally spaced apart incremental regions along the scan line associated with the particular one of said n analog signals that is currently being supplied by said surveillance system;

first clock means connected for supplying said first clock signal to said analog-to-digital converter, said first clock means including means for establishing the pulse repetition rate of said first clock signal proportional to the magnitude of an applied first control signal;

first clock control means connected for supplying said first control signal to said first clock means, said first clock control means including means for establishing said first control signal proportional to the cosine of the angle formed between said azimuthal axis and the scan line associated with that one of said n analog signals currently being supplied by said surveillance system, said first clock control means further including means for determining the number of digital signal values produced by said analog-to-digital converter during the time interval during which each particular one of said n analog signals is supplied by said surveillance system including means for establishing said number of digital signal values equal to m when an analog signal that is associated with a scan line which forms the smallest angle with said azimuthal axis is supplied by said surveillance system;

memory means connected for receiving and storing said digital signal values supplied by said analog-to-digital converter, said memory means being addressable as a rectangular memory array having n column addresses and m row addresses;

memory control means interconnected with said memory means for loading each series of digital signal values supplied by said analog-to-digital converter into one of said n columns of said memory array with said series of digital signal values representing said n successive analog signals being loaded into corresponding successive column addresses of said memory array, and with the successive digital signal values of each of said series of digital signal values being loaded into successive row addresses of said memory array, said memory control means further including means for accessing the digital signal values stored at each of said row addresses of said memory array;

digital signal means connected to said memory means for sequentially reading the digital signal values stored at each row address that is accessed by said memory control means, said digital signal means including means responsive to an applied second clock signal for sequentially reading the digital signal values of an accessed row address at a rate that is determined by the pulse repetition rate of said second clock signal;

second clock means connected for supplying said second clock signal to said data signal means, said second clock means including means for establishing the pulse repetition rate of said second clock signal proportional to the magnitude of an applied second control signal;

second clock control means connected for supplying said second control signal to said second clock means, said second clock control means including means for establishing said second control signal proportional to the row address of the particular row of digital signal values being accessed by said memory control means to decrease said pulse repetition rate of said second clock signal as successive rows of digital signal values are accessed; and

a digital-to-analog converter circuit connected for receiving said digital signal values as they are successively read by said digital signal means, said digital-to-analog converter for supplying said video information signal that is supplied by said digital scan converter.

13. The digital scan converter of claim 12 wherein said second clock control means further includes modulation means for varying the rate at which successive digital signal values of each row of accessed digital signal samples are read as a function of the column address of the digital signal value being read.

14. The digital scan converter of claim 13 wherein said modulation means includes means for establishing said variation in reading rate proportional to the tangent of the angle formed between said azimuthal axis and the scan line that corresponds to the analog signal resulting in the digital signal value stored at each particular column address of said row of digital signal values being read.

15. The digital scan converter of claims 12, 13 or 14 wherein said means for determining said number of digital signal values produced by said analog-to-digital converter comprises means for selectively coupling said first clock signal to said analog-to-digital converter at the time at which the analog signal currently being supplied by said surveillance system corresponds to signal reflection occurring from an incremental region of said surveillance region that is to be displayed on said first one of said m lines of image display and means for disconnecting said first clock signal from said analog-to-digital converter a predetermined time after said surveillance system emits the pulse of energy along the scan line that corresponds to said analog signal currently being supplied by said surveillance system.

16. The digital scan converter of claim 15 wherein said first clock means is energized and deenergized by an applied third control signal and said first clock control means includes means for supplying said third clock signal at a value which energizes said first clock means coincident with the time at which said analog signal currently being supplied by said surveillance system corresponds to signal reflection occurring from an incremental region of said surveillance region that is located a predetermined distance from said incremental regions that are to be displayed on said first line of said m lines of said image display relative to said second coordinate axis of said Cartesian coordinate system and means for supplying said third control signal at a value that deenergizes said first clock means at a time no later than the time at which said surveillance system supplies the next signal of said sequence of n analog signals.

17. The digital scan converter of claim 16 wherein said display device to be driven by said video information signal is a raster-scan television system and each of said consecutive intervals of said video information signal correspond to one horizontal sweep period of said raster-scan television system, said digital scan converter further comprising signal generating means for supplying a horizontal sync signal for determining the horizontal sweep intervals of said raster-scan television system and for supplying a vertical sync signal for vertical timing of said raster-scan television system and an output buffer memory connected to said memory means for temporarily storing the digital signal values stored at each particular row address of said memory means, said output buffer memory means being responsive to said horizontal sync signal for reading the row of digital signal values accessed by said memory control means into said output buffer memory during the retrace interval of one of said horizontal sweep intervals and for supplying that row of said digital signal values for reading by said digital signal means during the nextmost subsequent horizontal sweep interval.

18. The digital scan converter of claim 17 wherein said second clock means is energized and deenergized by an applied fourth control signal and said second clock control means includes means responsive to said horizontal sync signal for supplying said fourth control signal at a level that deenergizes said second clock means until a predetermined number of horizontal timing intervals of each vertical timing period of said raster-scan television system have occurred.