JP2006003140A - Marker for three-dimensional measurement - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a marker for three-dimensional measurement wherein measurement accuracy is not reduced even when rotation or a tilt is generated. <P>SOLUTION: A light-emitting diode (LED) 3 is installed on each face 2 of a polyhedral object 1. The polyhedral object 1 has shape symmetric with respect to a point 4 that is the center thereof, and is fixed to a base 6 by a fixed shaft 5. A spherical light diffusing plate 7 is disposed such that the spherical light diffusing plate 7 covers the whole of the polyhedral object 1 installed with the light-emitting diodes 3, and that the center accords with the point 4. The light diffusing plate 7 comprises a plate for scattering and diffusing light in every direction without reducing light intensity itself as thoroughly as possible. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a technique for improving the measurement accuracy of a three-dimensional measurement marker.

  Conventionally, for example, in order to measure the three-dimensional displacement of a large object manufactured at a factory as a construction element of a large structure such as a building, a technique of attaching a marker to the large object has been adopted. This marker is mounted at a position to be measured on a large object and is imaged from a plurality of imaging positions (most simply using a plurality of cameras), thereby obtaining a three-dimensional coordinate from the two-dimensional coordinates of the position. It is for seeking. As such a marker, those having various shapes are used. For example, Patent Document 1 discloses a diamond-shaped marker.

JP 09-189513 A

  When the rhombus marker is rotated or tilted, the apparent area viewed from the camera may change. If the apparent area changes, the integrated luminance value obtained when the center of gravity is calculated changes (that is, the luminance profile changes), so the accuracy of the obtained center of gravity changes depending on the rotation and inclination. Therefore, in a noisy environment, the obtained center of gravity value changes depending on the rotation and inclination, so that there is a problem that measurement accuracy is lowered.

  In 3D measurement, a circular marker may be used instead of a rhombus, but as with the rhombus, the apparent area changes due to rotation and tilt, resulting in a decrease in measurement accuracy. was there.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a three-dimensional measurement marker that does not reduce measurement accuracy even when rotation or tilt occurs.

  In order to solve the above-described problem, the 3D measurement marker according to the first invention is mounted at a position to be measured and is imaged from a plurality of imaging positions to obtain 3D coordinates from the 2D coordinates of the position. The three-dimensional measuring marker comprises a polyhedral object and light emitting means arranged on each surface of the polyhedral object.

  The 3D measurement marker according to the second invention is a 3D measurement marker for obtaining a 3D coordinate from a 2D coordinate of a position by being mounted at a position to be measured and captured from a plurality of imaging positions. A spherical light diffusing means, a light emitting means for irradiating the light diffusing means with light from outside the light diffusing means, a light diffusing means and a light diffusing means arranged so as to cover the light diffusing means and diffusing the light diffused in the light diffusing means And a light diffusing plate.

  The three-dimensional measurement marker according to the first invention comprises a polyhedral object, and light emitting means arranged on each surface of the polyhedral object, and the three-dimensional measurement marker according to the second invention is spherical A light diffusing means, a light emitting means for irradiating the light diffusing means with light from outside the light diffusing means, a light diffusing plate disposed so as to cover the light diffusing means and the light diffusing means and diffusing the light diffused in the light diffusing means, The luminance profile hardly changes even when it is rotated or tilted. Therefore, in these three-dimensional measurement markers, the feature point positions calculated by the calculation using the luminance profile hardly change. Therefore, highly accurate measurement can be performed.

<Embodiment 1>
FIG. 1 is a configuration diagram showing a marker 100 for three-dimensional measurement according to the first embodiment.
In FIG. 1, elements other than the polyhedral object 1 are shown in cross section. The marker 100 is attached to a position to be measured on a large object, and is imaged from a plurality of imaging positions (most simply using a plurality of cameras), whereby the two-dimensional coordinates of the positions are converted into three-dimensional coordinates. Is for seeking.

  In FIG. 1, a light emitting diode (LED) 3 is mounted on each surface 2 of a polyhedral object 1. The polyhedral object 1 has a symmetrical shape with respect to the center point 4 and is fixed to the pedestal 6 by a fixed shaft 5. The spherical light diffusing plate 7 covers the entire polyhedral object 1 on which the light emitting diode 3 is mounted, and is arranged so that the center thereof coincides with the point 4. This light diffusing plate 7 is composed of a plate for scattering and diffusing light in all directions while reducing the amount of light itself as much as possible.

  Since the normal line of each surface 2 of the polyhedral object 1 passes through the point 4, the light from the light emitting diode 3 is considered to radiate almost isotropically from the point 4. When the emitted light reaches the light diffusing plate 7, it is diffused and scattered within the light diffusing plate 7. As a result, the luminance of the surface of the light diffusing plate 7 becomes substantially uniform, and a luminance profile suitable for the calculation for calculating the feature point position can be formed. Here, the calculation for calculating the feature point position refers to an operation for obtaining the position to an accuracy of one pixel or less by luminance center of gravity calculation or function fitting. Moreover, since the light diffusing plate 7 has a solid angle of more than a hemisphere (that is, a solid angle of 2π or more), it is observed in a substantially spherical shape when viewed from any direction. Therefore, even when the marker 100 is rotated or tilted, the luminance profile hardly changes, so that the feature point position calculated by the above calculation hardly changes. Therefore, highly accurate measurement can be performed.

  The number of faces of the polyhedral object 1 is arbitrary, and the larger the number, the more light-emitting diodes 3 can be attached and the overall luminance is improved, so that the measurement accuracy is high, but it is 20 faces or more. desirable. Below, the reason is demonstrated using FIGS.

  FIG. 2 is a diagram showing the positional relationship between the polyhedral object 1, the light emitting diode 3, and the light diffusing plate 7 in the marker 100. In FIG. 2, the radiation angle θ of the light emitting diode 3 (the apex angle of the conical light emitted from the light emitting diode 3) and the angle α formed by the adjacent surfaces 2 of the polyhedral object 1 (in other words, the polyhedral object 1). The angle formed by the normals of the adjacent surfaces 2), the radius r1 of the light diffusing plate 7, and the distance r2 between the surface 2 and the point 4 of the polyhedral object 1 satisfy the following equation (1). In this case, it is known that the inner surface of the light diffusing plate 7 is uniformly irradiated with light.

r1 × (α / 2) <(r1−r2) × (θ / 2) (1)
Here, the following formula (2) is obtained by rearranging the formula (1) with the dimensional ratio R = r2 / r1.

α <θ × (1-R) (2)
FIG. 3 is a graph showing the relationship between the dimensional ratio R and the angle α using the upper limit value of α in Equation (2) for the radiation angles θ = 45 °, 90 °, and 120 °.

  By the way, various types of light emitting diodes 3 are commercially available, and the emission angle θ ranges from a narrow angle type of about 10 ° to a wide angle type of about 140 °. Is easily available with a radiation angle θ of 90 ° or less. Further, when the value of the dimensional ratio R is too small, the distance between the light emitting diode 3 and the light diffusing plate 7 becomes too large, so that the luminance in the light diffusing plate 7 is lowered. Therefore, practically, the value of the dimension ratio R is desirably 0.5 or more. Therefore, in the equation (2), when θ <90 ° and R> 0.5, the following equation (3) is obtained, and the range of α is determined.

α <45 ° (3)
FIG. 4 shows an example of the angle α formed between the adjacent surfaces 2 of the polyhedral object 1 having a representative number of surfaces. As shown in FIG. 4, as the number of faces increases, the angle α decreases. Since α is preferably 45 ° or less as shown in Expression (3), it can be seen from FIG. 4 that the number of faces of the polyhedral object 1 is preferably approximately 20 or more.

  As described above, the larger the number of faces of the polyhedral object 1 is, the more the overall luminance is improved. However, in order to obtain uniform luminance over the entire light diffusion plate 7, the shape of the polyhedral object 1 is point 4. It is desirable that The 32-hedron is also called a truncated icosahedron and has a shape obtained by cutting off the apex of the regular icosahedron. Therefore, there are a plurality of angles formed by adjacent surfaces 2 in the 32-hedron. The largest of them is about 42 °, like the regular icosahedron, and the shape is symmetric with respect to the point 4. Therefore, in the 32-hedron, the angle α is 45 ° or less, the shape is symmetric with respect to the point 4, and the number of faces is larger than that of the regular icosahedron, so that the shape of the polyhedron-like object 1 is a 32-hedron. By using, the measurement accuracy by the marker 100 can be further enhanced.

  Since the marker 100 uses the light emitting diode 3 as the light emitting means, it is possible to reduce power consumption necessary for light emission. Accordingly, since the battery can be driven, a power supply cable is not required, and handling can be facilitated. Further, by using the light emitting diode 3, it is possible to increase durability and extend the life. Further, by using a chip-type light emitting diode 3, it is possible to easily attach the polyhedral object 1.

  Although various application destinations can be considered for the marker 100 according to the present embodiment, for example, the marker 100 may be applied to a vibration test apparatus for measuring a building collapse process caused by a large earthquake. In such measurement, since the target object is very large, from several meters to several tens of meters, a marker with a large size is required to perform image processing such as calculation of feature point positions. The marker preferably has a light emitting means for facilitating the distinction from the background, but conventionally there has been no large light emitting marker that assumes such an application destination. In the marker 100 according to the present embodiment, use of the chip-type light emitting diode 3 makes it easy to mount and reduce power consumption, so that the size can be easily increased. Therefore, it is possible to measure with sufficient accuracy in an application with a relatively large displacement.

<Embodiment 2>
FIGS. 5 to 7 show measurement examples of the luminance profile of the marker 100 when a chip type is used as the light emitting diode 3 and a 32-hedron is used as the polyhedral object 1. 5 to 7, the horizontal axis represents pixels, and the vertical axis represents the light amount level. 5-7, the light transmittance of the light diffusing plate 7 is different. That is, in FIGS. 5 to 7, the light transmittance is in order of 86%, 58%, and 37%.

  The light transmittance is obtained by dividing the light amount of all light reaching the surface opposite to the incident surface by the incident light amount when the light beam is incident on a predetermined surface of the object. The incident light reaches the opposite surface as direct light when passing directly through the object. Moreover, a part of the scattered light that has been scattered one or more times within the object reaches the opposite surface. If such scattered light reaching the opposite surface is called transmitted scattered light, the light transmittance is the sum of the direct light amount and the transmitted scattered light amount divided by the incident light amount. In other words.

  In a general light diffusing plate, a low light transmittance means that the ratio of scattered light to direct light is high (high diffusion). Conversely, a high light transmittance means that scattered light is scattered. This means that the ratio of direct light to is high (low diffusion).

  The light transmittance described above is defined in the same manner for a light attenuating device such as a neutral density filter (ND filter). However, in a filter (particularly an ND filter), the ratio of transmitted scattered light to direct light is extremely low, and thus the light transmittance may indicate the ratio of direct light to the amount of incident light. That is, the light transmittance may represent a light shielding performance in the filter.

  5 and 6, since the direct light from each light emitting diode 3 is measured, the luminance profile has an irregular shape that is not suitable for the calculation of the feature point position. On the other hand, in FIG. 7, since the direct light from each light emitting diode 3 is no longer detected, the luminance profile has a substantially uniform shape suitable for the calculation of the feature point position. In FIG. 6, when the light transmittance is 58%, the diffusivity is insufficient, and when the light transmittance is 37% in FIG. 7, the light diffuser is sufficiently diffused. It can be seen that the required light transmittance is approximately 40% or less. By using such a light diffusing plate 7, the shape of the brightness profile of the marker 100 can be made uniform, so that sufficient measurement accuracy can be obtained even when the marker 100 is rotated or tilted. it can.

  Moreover, as a material of the light diffusing plate 7 having the light transmittance as described above, plastic, glass, and the like are conceivable, but in order to reduce the weight, plastic is desirable. Further, by using plastic, the risk of scattering when the marker 100 is damaged due to dropping or the like can be reduced and safety can be enhanced.

<Embodiment 3>
FIG. 8 is a configuration diagram showing a marker 200 for three-dimensional measurement according to the third embodiment.

  In FIG. 8, the light-emitting diode 3 is arranged not on the polyhedral object 1 but on the pedestal 6 in FIG. 1, and instead of the polyhedral object 1, a light diffusing sphere 8 as a spherical light diffusing means is fixed to the fixed axis 5. Is fixed to the pedestal 6. The light diffusing sphere 8 is arranged so that the center thereof coincides with the point 4 as in the polyhedral object 1 in FIG. Here, unlike the light diffusion plate 7, the light diffusion sphere 8 is filled with a material up to the inside thereof. In FIG. 8, the same elements as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted here.

  The light emitted from the light emitting diode 3 toward the point 4 reaches the light diffusion sphere 8 and is scattered by the light diffusion sphere 8. The light scattered by the light diffusion sphere 8 reaches the light diffusion plate 7 and is also scattered by the light diffusion plate 7. As a result, the luminance of the surface of the light diffusing plate 7 can be made substantially uniform.

  Thus, since the marker 200 according to the present embodiment uses the light diffusing sphere 8 instead of the polyhedral object 1, it has the same effect as the first embodiment.

FIG. 3 is a configuration diagram illustrating a three-dimensional measurement marker according to Embodiment 1. FIG. 3 is a configuration diagram illustrating a three-dimensional measurement marker according to Embodiment 1. 4 is a graph showing characteristics of the three-dimensional measurement marker according to Embodiment 1. FIG. 6 is a diagram illustrating characteristics of a three-dimensional measurement marker according to Embodiment 2. 6 is a graph showing characteristics of a three-dimensional measurement marker according to Embodiment 2. 6 is a graph showing characteristics of a three-dimensional measurement marker according to Embodiment 2. 6 is a graph showing characteristics of a three-dimensional measurement marker according to Embodiment 2. FIG. 10 is a configuration diagram illustrating a three-dimensional measurement marker according to a third embodiment.

Explanation of symbols

1 polyhedral object, 2 surfaces, 3 light emitting diodes, 4 points, 5 fixed axes, 6 pedestals, 7 light diffusion plates, 8 light diffusion spheres, 100, 200 markers.

Claims (7)

A marker for three-dimensional measurement for obtaining a three-dimensional coordinate from a two-dimensional coordinate of the position by being mounted at a position to be measured and imaged from a plurality of imaging positions,
A polyhedral object,
A three-dimensional measurement marker comprising: light emitting means arranged on each surface of the polyhedral object. The three-dimensional measurement marker according to claim 1,
A marker for three-dimensional measurement, further comprising a light diffusing plate that is disposed so as to cover the polyhedral object and the light emitting means and diffuses light emitted from the light emitting means. The three-dimensional measurement marker according to claim 1 or 2,
The three-dimensional measurement marker, wherein the polyhedral object has 20 or more surfaces. The three-dimensional measurement marker according to claim 3,
The three-dimensional measurement marker according to claim 1, wherein the polyhedral object is a 32-hedral object. The three-dimensional measurement marker according to any one of claims 2 to 4,
The three-dimensional measurement marker, wherein the light diffusion plate has a light transmittance of 40% or less. A three-dimensional measurement marker for obtaining a three-dimensional coordinate from a two-dimensional coordinate of the position by being mounted at a position to be measured and imaged from a plurality of imaging positions,
A spherical light diffusing means;
A light emitting means for irradiating the light diffusing means with light from outside the light diffusing means;
A light diffusing plate disposed so as to cover the light diffusing means and the light emitting means and diffusing the light diffused in the light diffusing means;
A marker for three-dimensional measurement, comprising: The three-dimensional measurement marker according to any one of claims 1 to 6,
The three-dimensional measuring marker, wherein the light emitting means includes a chip type light emitting diode.

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