Position measurement apparatus for measuring position of object having reflective surface in the three-dimensional space

Patent metadata

Field	Value
Publication number	US-10210628-B2
Application number	US-201415120682-A
Country	US
Kind code	B2
Filing date	Jul 31, 2014
Priority date	Mar 3, 2014
Publication date	Feb 19, 2019
Grant date	Feb 19, 2019

Abstract

A storage device stores capturing conditions including a viewpoint position and a shooting direction of the camera, model data including a shape of a segmented mirror, and feature point data representing a positional relationship among a viewpoint position and feature points. A camera captures the segmented mirror having a reflective surface to obtain a captured image including at least a part of the reflective surface. A marker object has feature points, and is fixed at a predetermined position with respect to the camera. A feature-point extracting unit extracts multiple feature points from a captured image in which the feature points are reflected in the reflective surface, and determines positions of the feature points within the captured image. A position measuring unit calculates a position of the segmented mirror, based on the capturing conditions, the model data, the feature point data, and the positions of the feature points within the captured image.

First claim

The invention claimed is:

1. A position measurement apparatus comprising:
a camera to capture an image including at least a part of a reflective surface of a target object;
a first memory to store capturing conditions including a viewpoint position and a shooting direction of the camera;
a second memory to store model data including a shape of the target object;
a marker object having a plurality of feature points and being fixed at a predetermined position with respect to the camera, the marker object being separated from the target object, wherein the camera captures a mirror image of the marker object reflected in the at least part of the reflective surface of the target object, when capturing the image including the at least part of the reflective surface of the target object;
a third memory to store feature point data representing a mutual positional relationship among the viewpoint position and the feature points;
a processor configured to
extract multiple feature points of the plurality of feature points from a captured image that is captured by the camera, the captured image including the mirror image of the marker object, the mirror image including the multiple feature points on the marker object,
determine positions of the extracted multiple feature points within the captured image,
calculate a position of the target object, based on the capturing conditions stored in the first memory, the model data stored in the second memory, the feature point data stored in the third memory, and the positions of the extracted multiple feature points within the captured image, and
output the calculated position of the target object.

2. The position measurement apparatus as claimed in claim 1 ,
wherein the target object has the reflective surface and non-reflective portions,
wherein the model data includes a shape of the reflective surface, including a curvature radius of the reflective surface, and includes a positional relationship among the reflective surface and the non-reflective portions, and
wherein the processor is further configured to calculate positions of a plurality of the feature points included in a mirror-image object of the marker object virtually existing at an opposite side of a side including the marker object with respect to the reflective surface, based on the feature point data, the processor obtaining a virtual captured image by virtually capturing the mirror-image object under the capturing conditions and calculating positions of the feature points within the virtual captured image to be close to positions of a plurality of the corresponding feature points within the captured image,
calculate a position and an orientation of the reflective surface, based on the positions of the feature points on the marker object determined according to the viewpoint position and the feature point data, the calculated positions of the feature points on the mirror-image object, and the curvature radius of the reflective surface, and
determine the position of the target object, based on the positional relationship among the reflective surface and the non-reflective portions, and based on the calculated position and orientation of the reflective surface.

3. The position measurement apparatus as claimed in claim 2 , wherein the processor calculates the positions of the plurality of the feature points included in the mirror-image object to reduce differences between the positions of the feature points within the virtual captured image and the positions of the corresponding feature points within the captured image.

4. The position measurement apparatus as claimed in claim 3 , wherein the processor is further configured to:
determine a projective transformation to be applied to the positions of the feature points within the captured image or to the positions of the feature points within the virtual captured image, the projective transformation being determined so that, by applying the projective transformation, a figure formed by the feature points within the virtual captured image and a figure formed by the corresponding feature points within the captured image are made geometrically more similar to each other,
determine, after applying the determined projective transformation to the positions of the feature points within the captured image or to the positions of the feature points within the virtual captured image, a resizing factor to be applied to the figure formed by the feature points within the virtual captured image or to the figure formed by the corresponding feature points within the captured image, the resizing factor being determined to reduce differences between the positions of the feature points within the virtual captured image and the positions of the corresponding feature points within the captured image by applying the resizing factor, and
calculate the positions of the plurality of the feature points included in the mirror-image object, based on the determined projective transformation and the determined resizing factor.

5. The position measurement apparatus as claimed in claim 2 ,
wherein the model data includes a reflective-surface model that represents the shape of the reflective surface, and
wherein the processor determines a position and an orientation of an approximate plane approximating the reflective surface near an intersection of the reflective surface and a straight line, the straight line passing through the viewpoint position and being perpendicular to the reflective surface, and determines a position and an orientation of the reflective-surface model so that the reflective-surface model is tangent to the approximate plane at the intersection, thereby determining the position and the orientation of the reflective surface.

6. The position measurement apparatus as claimed in claim 1 ,
wherein the target object has the reflective surface and non-reflective portions,
wherein the model data includes a shape of the reflective surface, and a positional relationship among the reflective surface and the non-reflective portions, and
wherein the processor is further configured to
calculate a position and an orientation of the reflective surface, based on the shape of the reflective surface and the feature point data, the processor obtaining a virtual captured image by virtually capturing under the capturing conditions, a plurality of feature points reflected in the reflective surface whose position and orientation are virtually determined, calculating positions of the plurality of the feature points included in the virtual captured image and calculating the position and the orientation of the reflective surface so that the positions of the plurality of the feature points within the virtual captured image are close to positions of a plurality of the corresponding feature points within the captured image, and
determine the position of the target object, based on a positional relationship among the reflective surface and the non-reflective portions, and based on the calculated position and orientation of the reflective surface.

7. The position measurement apparatus as claimed in claim 6 , wherein the processor calculates the position and the orientation of the reflective surface so as to reduce differences between the positions of the feature points within the virtual captured image and the positions of the corresponding feature points within the captured image.

8. The position measurement apparatus as claimed in claim 7 , wherein the processor is further configured to
determine a projective transformation to be applied to the positions of the feature points within the captured image or to the positions of the feature points within the virtual captured image, the projective transformation being determined so that, by

Assignees

• Mitsubishi Electric Corp

Inventors

• Domae Yukiyasu
• Seki Makito
• Watanabe Shintaro
• Sofuku Satoru
• Ezaki Yutaka

Classifications

• G06T7/70 Primary

  Determining position or orientation of objects or cameras (camera calibration G06T7/80) · CPC title

• G01B11/002 Primary

  for measuring two or more coordinates · CPC title

• G06T2207/30204

  Marker · CPC title

• G06K9/4604

  Physics · mapped topic

• H04N7/183

  for receiving images from a single remote source · CPC title