Learning the distance between cameras for articulated vehicles

Abstract

When calculating true inter-camera distance, offset images of a reference object such as a lane marker from at least two cameras coupled to an articulating vehicle are overlaid and shifted until the reference objects in each image are aligned. The distance by which the reference object images are shifted, as well as any rotation required to align the images, is used to calculate the actual distance between the cameras and to compensate for average yaw angle between the cameras when positioning the images for digital stitching to generate a composite “surround view” image.

Having thus described the preferred embodiments, the invention is now claimed to be: 
     
         1 . A system that facilitates determination of the true inter-camera distance (TICD) between cameras mounted on separate portions of an articulated vehicle, comprising:
 a first camera;   a second camera; and   a processor configured to:
 receive from the first camera a first image frame comprising a first image of a reference object; 
 receive from the second camera a second image frame comprising a second image of the reference object; 
 overlay the first and second images thereby generating a composite image of the reference object; 
 shift the first and second images until they are aligned; and 
 calculate the TICD between the first and second cameras as a function of the distances by which first and second images are shifted during alignment. 
   
     
     
         2 . The system according to  claim 1 , wherein the first and second cameras capture image frames asynchronously. 
     
     
         3 . The system according to  claim 2 , wherein the processor is further configured to:
 calculate a distance uncertainty due to vehicle motion (DUFM) as a function of vehicle speed and a frame start time difference (DFST) between respective image capture start times of the first and second cameras.   
     
     
         4 . The system according to  claim 1 , wherein the processor is further configured to:
 calculate the true inter-camera distance (TICD) such that
   TICD=(speed ratio*shift1)−(shift2)/(speed ratio−1)  (5)
 
   where Shift1 is the amount by which the reference point or object in the image is shifted at a first speed, Shift2 is the amount by which the reference point or object in the second image is shifted at a second speed, and speed ratio is the ratio of the second speed to the first speed.   
     
     
         5 . The system according to  claim 1 , wherein the processor is further configured to:
 rotate at least one of the first and second images when aligning the second image with the first image; and   calculate, across a plurality of composite images, an average rotation required to angularly align the first and second images.   
     
     
         6 . The system according to  claim 5 , wherein the processor is further configured to generate a surround view that is a composite view of the first and second camera images, adjusted to compensate for vehicle motion and yaw using the calculated TICD and the calculated average rotation. 
     
     
         7 . The system according to  claim 1 , wherein the first camera is mounted on a first portion of the articulated vehicle, and the second camera is mounted on a second portion of the articulated vehicle, the second portion being coupled to the first portion by an articulating coupling. 
     
     
         8 . The system according to  claim 1 , further comprising a plurality of cameras, wherein the processor is configured to calculate a TICD between all permutations of pairs of cameras in the plurality of cameras and to generate a surround view that is a composite view of a plurality of images captured by the respective cameras. 
     
     
         9 . A method of calculating a true inter-camera distance (TICD) between cameras mounted on separate portions of an articulated vehicle, comprising:
 receiving from a first camera a first image frame comprising a first image of a reference object;   receiving from a second camera a second image frame comprising a second image of the reference object;   overlaying the first and second images thereby generating a composite image of the reference object;   shifting the first and second images until they are aligned; and   calculating the TICD between the first and second cameras as a function of the distances by which first and second images are shifted during alignment.   
     
     
         10 . The method according to  claim 9 , further comprising:
 calculating a distance uncertainty due to vehicle motion (DUFM) as a function of vehicle speed and a frame start time difference (DFST) between respective image capture start times of the first and second cameras.   
     
     
         11 . The method according to  claim 9 , further comprising:
 calculating the true inter-camera distance such that
   TICD=(speed ratio shift1)−(shift2)/(speed ratio−1)  (5)
 
   where Shift1 is the amount by which the reference point or object in the first image is shifted at a first speed, Shift2 is the amount by which the reference point or object in the second image is shifted at a second speed, and speed ratio is a ratio of the second speed to the first speed.   
     
     
         12 . The method according to  claim 9 , further comprising:
 rotating at least one of the first and second images when aligning the second image with the first image; and   calculating, across a plurality of composite images, an average rotation required to angularly align the first and second images.   
     
     
         13 . The method according to  claim 12 , further comprising generating a surround view that is a composite view of the first and second camera images, adjusted to compensate for vehicle motion and yaw using the calculated TICD and the calculated average rotation. 
     
     
         14 . The method according to  claim 9 , wherein the first camera is mounted on a first portion of the articulated vehicle, and the second camera is mounted on a second portion of the articulated vehicle, the second portion being coupled to the first portion by an articulating coupling. 
     
     
         15 . The method according to  claim 9 , further comprising calculating a TICD between all permutations of pairs of cameras in a plurality of cameras mounted on the articulating vehicle, and generating a surround view that is a composite view of a plurality of images captured by the respective cameras. 
     
     
         16 . A computer-readable medium having stored thereon instructions for performing the method according to  claim 9 . 
     
     
         17 . A processor configured to execute computer-executable instructions for calculating a true inter-camera distance (TICD) between cameras mounted on separate portions of an articulated vehicle, the instructions comprising:
 receiving from a first camera a first image frame comprising a first image of a reference object;   receiving from a second camera a second image frame comprising a second image of the reference object;   overlaying the first and second images thereby generating a composite image of the reference object;   shifting the first and second images until they are aligned; and   calculating the TICD between the first and second cameras as a function of the distances by which first and second images are shifted during alignment.   
     
     
         18 . The processor according to  claim 17 , further configured to:
 calculate the true inter-camera distance such that
   TICD=(speed ratio*shift1)−(shift2)/(speed ratio−1)  (5)
 
   where Shift1 is the amount by which the reference point or object in the first image is shifted at a first speed, Shift2 is the amount by which the reference point or object in the second image is shifted at a second speed, and speed ratio is a ratio of the second speed to the first speed.   
     
     
         19 . The processor according to  claim 17 , further configured to:
 rotate at least one of the first and second images when aligning the second image with the first image; and   calculate, across a plurality of composite images, an average rotation required to angularly align the first and second images.   
     
     
         20 . The processor according to  claim 19 , further configured to generate a surround view that is a composite view of the first and second camera images, adjusted to compensate for vehicle motion and yaw using the calculated TICD and the calculated average rotation. 
     
     
         21 . The processor according to  claim 17 , further configured to calculate a TICD between all permutations of pairs of cameras in a plurality of cameras mounted on the articulating vehicle, and generate a surround view that is a composite view of a plurality of images captured by the respective cameras. 
     
     
         22 . An apparatus that facilitates calculating a true inter-camera distance (TICD) between cameras mounted on separate portions of an articulated vehicle, comprising:
 means for capturing a plurality of images of a reference object from at least two perspective points;   means for receiving from a first camera a first image frame comprising a first image of a reference object;   means for receiving from a second camera a second image frame comprising a second image of the reference object;   means for overlaying the first and second images thereby generating a composite image of the reference object;   means for shifting the first and second images until they are aligned; and   means for calculating the TICD between the first and second cameras as a function of the distances by which first and second images are shifted during alignment.