Position measuring apparatus using a pair of electronic cameras

• US 6,477,260 B1
• Filed: 10/26/1999
• Issued: 11/05/2002
• Est. Priority Date: 11/02/1998
• Status: Expired due to Fees

• Current Assignee: Nissan Motor Co., Ltd.
• Original Assignee: Nissan Motor Co., Ltd.
• Inventors: Shimomura, Noriko
• Primary Examiner(s): Mancuso, Joseph
• Assistant Examiner(s): Miller, Martin
• Application Number:
  US09/426,952
• Time in Patent Office: 1,106 Days
• Field of Search: 382/106, 382/104, 382/286, 382/199, 340/435, 340/901, 701/301, 701/302, 348/113, 348/116, 348/139, 348/140, 348/141, 348/142, 348/143, 348/169
• US Class Current: 382/106
• CPC Class Codes: G01S 11/12 using electromagnetic waves other than radio waves
• CPC Class Codes: G06T 2207/10012 Stereo images
• CPC Class Codes: G06T 7/593 from stereo images
• CPC Class Codes: G06T 7/74 involving reference images or patches
• CPC Class Codes: H04N 13/239 using two 2D image sensors having a relative position equal to or related to the interocular distance H04N13/243 takes precedence
• CPC Class Codes: H04N 2013/0081 Depth or disparity estimation from stereoscopic image signals

Abstract

A distance measuring apparatus applicable to a mobile body such as an automotive vehicle which detects a position of an obstacle (a target object) without influence of an ambient environment such as a white line and determines positions of lateral ends of the obstacle is disclosed. In the distance measuring apparatus, a pair of electronic cameras are mounted on the mobile body, optical axes of both of the cameras being mutually parallel to each other and being directed toward a forward direction or toward a rearward direction and horizontal axes of their photograph planes being aligned to the same line. Using a new stereophotographic image processing, deriving a parallax for each window from a calculated difference in position between one image and another image, voting to each position in a table of parallax x lateral position, calculating a distance to the obstacle on the basis of the value of the parallax at any one of horizontal positions in the table at which a result of voting indicates a higher value, deriving a horizontal range on the one image on the basis of the horizontal positions of respective windows corresponding to any positions in the table at each of which the result of voting indicates the higher value, deriving a vertical range at each end of which a histogram value of histograms indicates a higher value, and, selecting any one of present longitudinal edges located in the vicinity of each end of the horizontal range from among searched longitudinal edges.

Claims

1. A position measuring apparatus, comprising:

a pair of electronic cameras mounted on a mobile body, optical axes of both of the cameras being mutually parallel to each other and being directed toward a forward direction of the mobile body or toward a rearward direction thereof and horizontal axes of their photograph planes being aligned to the same line;

an image split region setting section to split one image photographed by one of the pair of cameras into a plurality of image split regions, each image split region having a predetermined dimension;

a parallax calculating section to determine, for each image split region, a similarity in image between an image present within one of the image split regions and another image photographed by the other of the pair of cameras and present on each position corresponding to one of the image split regions and to calculate, for each image split region, a difference in position between a position of each of the image split regions and any one of the positions of the other image at which the similarity in image to the image on the position of each image split region is highest, the parallax calculating section deriving a parallax for each image split region from the calculated difference in position therebetween;

a voting section, the voting section including a table whose lateral axis is made correspondence to a horizontal position for each image split region and whose longitudinal axis is made correspondence to a value of the parallax for each image split region and accumulatively adding a predetermined numerical value to each position in the table corresponding to both of the horizontal position of each image split region and a value of the parallax at the corresponding image split region of the same horizontal position so as to vote to each position in the table;

a distance calculating section to calculate a distance from a camera setting position of the pair of cameras to a target object to be detected present in either the forward direction or the rearward direction on the basis of the value of the parallax at any one of the horizontal positions in the table at which a result of voting by the voting section indicates a value higher than a first threshold value;

a horizontal range calculating section to derive a horizontal range on the one image over which the target object to be detected is photographed on the basis of the horizontal positions of the respective image split regions corresponding to any positions in the table at each of which the result of voting by the voting section indicates the value higher than the first threshold value;

a vertical range calculating section to derive first histograms on horizontal edges for each vertical coordinate value on the whole image within the horizontal range derived by the horizontal range calculating section and to derive a vertical range at each end of which a histogram value of the first histograms indicates a value higher than a second threshold value;

an edge selecting section to derive second histograms on vertical edge components for each horizontal coordinate value on the whole image within the vertical range derived by the vertical range calculating section, to search for longitudinal edges present on the one image determined from the second histograms, and to select any one of the longitudinal edges which is located in the vicinity of each end of the horizontal range derived by the horizontal range calculating section from among the searched longitudinal edges; and

an actual position calculating section to derive an actual spatial position on each lateral end of the target object present in either the forward or rearward direction with respect to the camera setting position, each lateral end thereof corresponding to the selected longitudinal edge on the one image, on the basis of the distance from the camera setting position to the target object derived by the distance calculating section and the coordinate value of each longitudinal edge selected by the edge selecting section.

2. A position measuring apparatus as claimed in claim 1, wherein the horizontal range calculating section includes:

a first determinator to determine an assured horizontal range A within which the photograph of the image of the target object to be detected is perfectly assured, the assured horizontal range A being determined by the first determinator in such a manner that when a horizontal range calculating process of deriving the horizontal range on the one image in which the target object to be detected is photographed on the basis of the horizontal positions corresponding to any positions in the table at each of which the result of voting by the voting section indicates the value higher than the first threshold value is repeated for a predetermined period of time, the image of the target object to be detected is determined to be present within the assured horizontal range A continuously in time within the predetermined period of time; and

a second determinator to determine a candidate horizontal range A′

within which the photograph of the image of the target object to be detected is assured with less probability than the assured horizontal range A, the candidate horizontal range A′

being determined by the second determinator in such a manner that when the horizontal range calculating process is repeated for the predetermined period of time, the image of the target object to be detected is determined to be present within the candidate horizontal range A′

not continuously in time but a predetermined number of times or more within the predetermined period of time, and wherein the vertical range calculating section derives the first histograms on the horizontal edges for each vertical coordinate value on the whole image within the assured horizontal range A.

3. A position measuring apparatus as claimed in claim 2, wherein the vertical range calculating section includes a searching section to search for the horizontal edges present within the assured horizontal range A to derive the vertical range B.

4. A position measuring apparatus as claimed in claim 2, wherein, when deriving the vertical range B, the vertical range calculating section derives approximate vertical coordinate positions HU and HD at which upper and lower ends of the target object to be detected are photographed on the image on the basis of the distance from the camera setting position to the target object derived by the distance calculating section, a focal length of each of the pair of the cameras, a height by which the pair of cameras are mounted on the mobile body, and a preset value of a height of the target object to be detected previously set according to an approximate height which is expected from a general dimension of the target object and selects vertical coordinate positions located in the vicinity of the approximate vertical coordinate positions HU and HD from among those at each of which the histogram value of the first histograms on the horizontal edges indicates the value higher than the second threshold value as respective ends of the vertical range B.

5. A position measuring apparatus as claimed in claim 3, wherein, when deriving the vertical range B, the vertical range calculating section derives approximate vertical coordinate positions HU and HD at which upper and lower ends of the target object to be detected are photographed on the image on the basis of the distance from the camera setting position to the target object derived by the distance calculating section, a focal length of each of the pair of the cameras, a height by which the pair of cameras are mounted on the mobile body, and a preset value of a height of the target object to be detected previously set according to an approximate height which is expected from a general dimension of the target object and selects vertical coordinate positions located in the vicinity of the approximate vertical coordinate positions HU and HD from among those at each of which the corresponding horizontal edge for which the vertical range calculating section is searched within the assured horizontal range A as respective ends of the vertical range B.

6. A position measuring apparatus as claimed in claim 2, wherein the edge selecting section includes:

an average calculator to calculate an average value of a luminance on each vertical coordinate value aligned in the same horizontal coordinate position within the vertical range B for each horizontal coordinate position; and

a first range determinator to determine a first horizontal range over which the average values calculated for the respective horizontal coordinate positions each of which is smaller than a predetermined average value are continued within the predetermined period of time as a second horizontal range over which at least one longitudinal edge is present.

7. A position measuring apparatus as claimed in claim 6, wherein the edge selecting section selects any one of the longitudinal edges which is located in the vicinity of each of both ends of the first horizontal range and which is located in the vicinity of an image zone interposed between the assured horizontal range A and the candidate horizontal range A′

.

8. A position measuring apparatus as claimed in claim 2, wherein the edge selecting section includes:

an variance calculator to calculate an average value of a luminance on each vertical coordinate value aligned in the same horizontal coordinate position within the vertical range B for each horizontal coordinate position and to calculate a variance of the average value of the luminance thereon; and

a first range determinator to determine a first horizontal range over which the variances of the average values calculated for the respective horizontal coordinate positions each of which is smaller than a predetermined variance value are continued within the predetermined period of time as a second horizontal range over which at least one longitudinal edge is present.

9. A position measuring apparatus as claimed in claim 2, wherein the vertical range calculating section derives the first histograms on an absolute value of horizontal differentiation to a luminance on each vertical coordinate value within the assured horizontal range A and wherein the edge selecting section derives the second histograms on an absolute value of vertical differentiation to the luminance on each vertical coordinate value within the vertical range derived by the vertical range calculation section.

10. A position measuring apparatus as claimed in claim 1, wherein the mobile body is an automotive vehicle and further comprising a device to determine whether the vehicle on which the distance measuring apparatus is mounted is to be forwarded to approach to the target object of a preceding vehicle which is running ahead of the vehicle at the same traffic lane as the vehicle or to be passed aside the target object of the preceding vehicle according to a result of determination of the lateral ends of the target object of the preceding vehicle by the actual position calculating section.