Position measurement system, position measurement method and computer readable medium

1. A position measurement system comprising:

an image capturing unit that captures first reference points which are three reference points on a plane arranged on a target and whose positional relation with each other is specified, and a second reference point which is a single reference point at a given distance away from the plane and whose positional relation with the first reference points is specified, wherein the second reference point is attached to the target;

an identifying unit that identifies images of the first reference points and an image of the second reference point on the basis of the positional relation among the images of the four reference points captured by the image capturing unit; and

a calculating unit that calculates a three-dimensional position and triaxial angles of the target on the basis of the positional relation between the images of the first reference points and the image of the second reference point identified by the identifying unit,

wherein the calculating unit specifies the plane including the first reference points on the target from the images of the first reference points identified by the identifying unit, and specifies a normal direction of the plane according to the image of the second reference point identified by the identifying unit.

2. The position measurement system according to claim 1 , wherein the second reference point captured by the image capturing unit is a point at the given distance away from the plane including the first reference points to the image capturing unit.

3. The position measurement system according to claim 1 , wherein

the calculating unit specifies a three-dimensional position of the first reference points on the basis of candidates of the three-dimensional position of the first reference points acquired based on the positional relation of the images of the first reference points, change in the positional relation among the images of the first reference points and the image of the second reference point based on the triaxial angles of the target, and a position of the image of the actual second reference point captured by the image capturing unit, and

the calculating unit specifies the three-dimensional position and the triaxial angles of the target on the basis of the specified three-dimensional position of the first reference points.

4. The position measurement system according to claim 1 , wherein

the second reference point captured by the image capturing unit is arranged at a position close to a center of gravity of a triangle formed by the first reference points relative to the first reference points, and

the identifying unit identifies an image at a position closest to a center of gravity of a quadrangle formed by the captured images of the four reference points as the image of the second reference point and identifies other three images as the images of the first reference points.

5. The position measurement system according to claim 1 , wherein

a triangle formed by the first reference points captured by the image capturing unit has a short side with length of two-third or less of length of other two sides, and

the identifying unit identifies a shortest side among the sides of the triangle formed by the images of the identified first reference points as the short side, and identifies the individual first reference points on the basis of positional relation between the specified short side and an image of one of the first reference points that is not located on the short side.

6. A position measurement system comprising:

an image capturing unit that captures first reference points which are three reference points on a plane arranged on a target and whose positional relation with each other is specified, a second reference point which is a single reference point at a given distance from the plane and whose positional relation with the first reference points is specified, and a third reference point which is arranged on the plane and whose positional relation with the first reference points is specified, wherein the second reference point is attached to the target;

an identifying unit that identifies images of the first reference points, an image of the second reference point and an image of the third reference point on the basis of positional relation among the images of the five reference points captured by the image capturing unit; and

a calculating unit that calculates a three-dimensional position and triaxial angles of the target on the basis of the positional relation between the images of the first reference points and the image of the second reference point identified by the identifying unit,

wherein the calculating unit specifies the plane including the first reference points on the target from the images of the first reference points identified by the identifying unit, and specifies a normal direction of the plane according to the image of the second reference point identified by the identifying unit.

7. The position measurement system according to claim 6 , wherein

the third reference point captured by the image capturing unit is arranged so that a line segment connecting one apex of a triangle formed by the first reference points with the third reference point is in parallel with a side held between other two apexes of the triangle, the third reference point is located at a terminal end of the line segment when a quadrangle including the line segment and the side is followed clockwise, and the line segment is shorter than the side, and

the identifying unit extracts a quadrangle having parallel two sides from the captured images of the five reference points, identifies, as the image of the third reference point, the image located on a shorter side of the two sides and at the terminal end of the quadrangle when the quadrangle is followed clockwise, and identifies the other three images as the images of the first reference points.

8. A position measurement system comprising:

an image capturing unit that captures first reference points which are three reference points on a plane arranged on a target and whose positional relation with each other is specified, a second reference point which is a single reference point at a given distance from the plane and whose positional relation with the first reference points is specified, and a third reference point which is arranged on the plane and whose positional relation with the first reference points is specified;

an identifying unit that identifies images of the first reference points, an image of the second reference point and an image of the third reference point on the basis of positional relation among the images of the five reference points captured by the image capturing unit; and

a calculating unit that calculates a three-dimensional position and triaxial angles of the target on the basis of the positional relation between the images of the first reference points and the image of the second reference point identified by the identifying unit, wherein:

the calculating unit specifies the plane including the first reference points on the target from the images of the first reference points identified by the identifying unit, and specifies a normal direction of the plane according to the image of the second reference point identified by the identifying unit,

the second reference point captured by the image capturing unit is arranged at a position close to a center of gravity of a triangle formed by the first reference points relative to the first reference points,

the third reference point captured by the image capturing unit is arranged so that a line segment connecting one apex of a triangle formed by the first reference points with the third reference point is in parallel with a side held between other two apexes of the triangle, the third reference point is located at a terminal end of the line segment when a quadrangle including the line segment and the side is followed clockwise, and the third reference point is located at a position far from the center of gravity of the triangle formed by the first reference points relative to the first reference points, and

the identifying unit extracts a quadrangle having parallel two sides from the captured images of the five reference points, identifies an image not included in the quadrangle as the image of the second reference point, specifies the images of the first reference points and a position of the center of gravity of the triangle formed by the first reference points on the basis of a position of the image of the second reference point, and specifies the image of the third reference point on the basis of the position of the center of gravity.

9. A position measurement system comprising:

an image capturing unit that captures first reference points which are three reference points on a plane arranged on a target and whose positional relation with each other is specified, a second reference point which is a single reference point at a given distance from the plane and whose positional relation with the first reference points is specified, and a third reference point which is arranged on the plane and whose positional relation with the first reference points is specified;

an identifying unit that identifies images of the first reference points, an image of the second reference point and an image of the third reference point on the basis of positional relation among the images of the five reference points captured by the image capturing unit; and

a calculating unit that calculates a three-dimensional position and triaxial angles of the target on the basis of the positional relation between the images of the first reference points and the image of the second reference point identified by the identifying unit, wherein:

the calculating unit specifies the plane including the first reference points on the target from the images of the first reference points identified by the identifying unit, and specifies a normal direction of the plane according to the image of the second reference point identified by the identifying unit,

the second reference point captured by the image capturing unit is arranged at a position close to a center of gravity of a triangle formed by the first reference points relative to the first reference points;

the third reference point captured by the image capturing unit is arranged at a position far from the center of gravity relative to the first reference points, on a straight line connecting one of the first reference points at a position farthest from the center of gravity of the triangle formed by the first reference points with the center of gravity; and

the identifying unit extracts three images aligned on a straight line from the captured images of the five reference points, identifies an image in the middle and two images not on the straight line as the images of the first reference points, identifies an image closest to the center of gravity of the triangle formed by the images of the first reference points as the image of the second reference point, and identifies an image farthest from the center of gravity as the image of the third reference point.

10. A position measurement method comprising:

using a camera to capture first reference points which are three reference points on a plane arranged on a target and whose positional relation with each other is specified, and a second reference point which is a single reference point at a given distance away from the plane and whose positional relation with the first reference points is specified, wherein the second reference point is attached to the target;

identifying images of the first reference points and an image of the second reference point on the basis of the positional relation among the images of the four reference points that are captured; and

calculating a three-dimensional position and triaxial angles of the target on the basis of the positional relation between the images of the first reference points and the image of the second reference point that are identified,

wherein the calculating of the three-dimensional position and the triaxial angles of the target comprises specifying the plane including the first reference points on the target from the images of the first reference points that are identified, and specifying a normal direction of the plane according to the image of the second reference point that is identified.

11. The position measurement method according to claim 10 , wherein the captured second reference point is a point at a given distance away from the plane including the first reference points.

12. A computer readable medium storing a program causing a computer to execute a process for measuring a position of a target, the process comprising:

identifying images of first reference points and an image of a second reference point on the basis of positional relation among images of four reference points acquired by capturing the first reference points which are three reference points on a plane arranged on a target and whose positional relation with each other is specified, and the second reference point which is a single reference point at a given distance from the plane and whose positional relation with the first reference points is specified by an image capturing unit, wherein the second reference point is attached to the target; and

calculating a three-dimensional position and triaxial angles of the target on the basis of the positional relation between the images of the first reference points and the image of the second reference point identified by an identifying unit,

wherein the calculating of the three-dimensional position and the triaxial angles of the target comprises specifying the plane including the first reference points on the target from the images of the first reference points that are identified and specifying a normal direction of the plane according to the image of the second reference point that is identified.

13. A position measurement method comprising:

identifying images of first reference points and an image of a second reference point on the basis of a positional relation among the images, wherein the first reference points are three reference points on a plane arranged on a target, a positional relation of the first reference points with each other is specified, the second reference point is a single reference point at a given distance from the plane, a positional relation of the second reference point with the first reference points is specified, and the second reference point is attached to the target; and

calculating, by using a processor, a three-dimensional position and triaxial angles of the target on the basis of the positional relation between the images of the first reference points and the image of the second reference point,

wherein the calculating of the three-dimensional position and the triaxial angles of the target comprises specifying the plane including the first reference points on the target from the images of the first reference points that are identified and specifying a normal direction of the plane according to the image of the second reference point that are is identified.