Relative azimuth measuring method and apparatus

• US 5,541,726 A
• Filed: 04/19/1994
• Issued: 07/30/1996
• Est. Priority Date: 04/19/1993
• Status: Expired due to Fees

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Nakajima, Shin-ichi
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): Laufer, Pinchus M.
• Application Number:
  US08/229,704
• Time in Patent Office: 833 Days
• Field of Search: 356/141.1, 356/152.2, 356/152.3, 359/527, 359/529, 359/530, 359/546, 359/547, 359/548, 359/541
• US Class Current: 356/141.1
• CPC Class Codes: G01S 17/06 Systems determining position data of a target
• CPC Class Codes: G01S 17/66 Tracking systems using electromagnetic waves other than radio waves

Abstract

A measuring section of a target tracer emits emergent light from a light source toward a reflector of a target by way of a half mirror of an optical system. The reflector has a light reflection factor increasing toward the center thereof and has areas of respective reflection factors arranged concentrically. Reflected light from the reflector passes through the mirror and is introduced to an imaging element. The imaging element scans a two-dimensional image of the reflector to generate electric signals composed of a plurality of corresponding picture elements. A threshold value comparing circuit selects those of the electric signals which are higher than a threshold value as azimuth signals. An angle calculating circuit calculates the center of the image of the reflector from the azimuth signals and calculates an azimuth angle and an elevation angle of the target with respect to the measuring section from a displacement of the center of the image from the center of a field of view of the imaging element. A threshold value controlling circuit increases the threshold value when the number of picture element of the azimuth signals is greater than a predetermined value, but decreases the threshold value when the number of picture elements of the azimuth signals is smaller than the predetermined value.

Claims

1. A relative azimuth measuring method wherein an azimuth angle and an elevation angle, that is, a relative azimuth, of a target with respect to a target tracer is measured using a light beam, wherein:

first, toward reflector means which is installed fixedly on said target and reflects incident light as reflected light in a direction opposite to an incidence direction of the incident light, light is introduced from measuring means installed fixedly on said target tracer, said reflector means having areas of respective reflection factors which form a concentrical regular polygonal multiple reflection area or a concentrical circular multiple reflection area where light reflector factors increase toward the center of said reflector means; and

on the other hand, on said target tracer, said measuring means inputs the reflected light reflected from said reflector means, produces a two-dimensional image of said reflector means from the reflected light, then converts the two-dimensional image by photo-electric conversion to obtain electric signals corresponding to a plurality of picture elements of the two-dimensional image, adopts only those of the electric signals which are higher in magnitude than a particular threshold value as azimuth signals and calculates the relative azimuth using the azimuth signals.

2. A relative azimuth measuring method as claimed in claim 1, wherein the threshold value is increased in magnitude thereof when the number of a plurality of picture elements constituting the two-dimensional image of said reflector means is greater than a predetermined value, but is decreased in magnitude conversely when said number of the plurality of picture elements is smaller than the predetermined value.

3. A relative azimuth measuring method as claimed in claim 2, wherein the predetermined value is determined so that the reflector image of one frame constituted from the azimuth signals may be accommodated in a field of view of an image screen of said measuring means.

4. A relative azimuth measuring method as claimed in claim 1, wherein a displacement of the center of the reflector image constituted from the azimuth signals from the center of a field of view of an image screen of said measuring means, and the relative azimuth is calculated from a value of the displacement and a horizontal angle and a vertical angle of the field of view of the image screen of said measuring means.

5. A relative azimuth measuring apparatus wherein an azimuth angle and an elevation angle, that is, a relative azimuth, of a target with respect to a target tracer is measured using a light beam, comprising:

reflector means installed fixedly on said target for reflecting incident light as reflected light in a direction opposite to an incident direction of the incident light, said reflector means having areas of respective light reflection factors which form a concentrical regular polygonal multiple reflection area or a concentrical circular multiple reflection area where light reflection factors increase toward the center of said reflector means; and

measuring means installed fixedly on said target tracer and including an optical system for emitting emergent light toward the direction of said reflector means and receiving reflected light of the emergent light reflected from said reflector means, an imaging element for forming a two-dimensional image of said reflector means from the reflected light inputted thereto from said optical system and converting the two-dimensional image by photo-electric conversion to produce a plurality of electric signals corresponding to a plurality of picture elements, and a relative azimuth calculating section for calculating a relative azimuth between said target and said target tracer in response to those of the electric signals which are higher in magnitude than a particular threshold value;

said relative azimuth calculating section including a threshold value comparing circuit for outputting those of the electric signals inputted thereto from said imaging element which are higher in magnitude than the threshold value as azimuth signals, a threshold value controlling circuit for calculating a number of picture elements of the azimuth signals for one frame of the two-dimensional image and increasing the threshold value when the counted picture number is greater than a predetermined value but decreasing the threshold value when the counted picture number is smaller than the predetermined value, and an angle calculating circuit for calculating a displacement of the center of the two-dimensional image constituted from the azimuth signals from the center of a field of view of a screen of said imaging element and calculating the relative azimuth from a value of the displacement and a horizontal angle and a vertical angle of the field of view of the screen of said measuring means.

6. A relative azimuth measuring apparatus as claimed in claim 5, wherein said reflector means is formed from concentrical multiple reflection areas having a plurality of small reflectors which form a hexagonal closest packing structure in each of said areas.

7. A relative azimuth measuring apparatus as claimed in claim 5, wherein said reflector means is formed from concentrical annular multiple reflection areas having a plurality of small reflectors in each of said areas.

8. A relative azimuth measuring apparatus as claimed in claim 6, wherein said reflector means is constituted from a single circular light reflecting body and has areas of equal reflection factors which are positioned on same concentrical rings and processed so that the reflection factor increases toward the area nearest to the center of said circular light reflecting body.

9. A relative azimuth measuring apparatus as claimed in claim 5, wherein said threshold value comparing circuit includes an analog/digital converter for converting the electric signals each in the form of an electric signal inputted thereto from said imaging element into digital electric signals, a comparator for outputting those of the digital electric signals which are higher than the threshold value as the azimuth signals, and a memory for storing the azimuth signals in sets of a horizontal coordinate and a vertical coordinate of the two-dimensional image for each of the picture elements, and said threshold value controlling circuit includes a counter for counting the number of the picture elements stored in said memory in units of a frame of the two-dimensional image, and a threshold value controller for increasing the threshold value in magnitude when the number of the picture elements of one frame counted by said counter is greater than a predetermined value but decreasing the threshold value in magnitude when the number of the picture elements of one frame is smaller than the predetermined value.

10. A relative azimuth measuring apparatus as claimed in claim 9, wherein the predetermined value is determined so that the two-dimensional image in units of a frame constituted from the azimuth signals may be accommodated in a field of view of an image screen of said imaging element.