Navigation in buildings with rectangular floor plan

Abstract

An apparatus and method for providing a direction based on an angle of a reference wall is provided. A mobile device uses an angle of a horizontal feature from an image to calibrate a sensor and future sensor measurements. The angle of the horizontal feature is determined by image processing and this angle is mapped to one of four assumed parallel or perpendicular angles of an interior of a building. A sensor correction value is determined from a difference between the sensor-determined angle and the image-processing determined angle. The image processing determined angle is assumed to be very accurate and without accumulated errors or offsets that the sensor measurements may contain.

What is claimed is: 
     
         1 . A method in a mobile device of navigation using wall matching with a horizontal feature to estimate motion, the method comprising:
 capturing, with a camera in the mobile device, a local image containing the horizontal feature;   processing the local image to determine a horizontal feature angle (θ HF ), wherein the horizontal feature angle (θ HF ) is an angle from a current orientation of the mobile device to the horizontal feature; and   estimating a direction of motion of the mobile device, based on the horizontal feature angle (θ HF ), as parallel to a wall angle of the horizontal feature.   
     
     
         2 . The method of  claim 1 , wherein the local image comprises an interior wall. 
     
     
         3 . The method of  claim 1 , further comprising:
 determining a reference angle (θ REF ) of a reference wall, wherein the reference angle (θ REF ) is an absolute angle with respect to North; and   selecting a wall angle, of the horizontal feature, equal to an integer multiple of 90° from the reference angle (θ REF ).   
     
     
         4 . The method of  claim 3 , wherein the reference wall is an exterior wall. 
     
     
         5 . The method of  claim 3 , wherein determining the reference angle (θ REF ) comprises:
 determining a building containing the reference wall; and 
 determining the reference angle (θ REF ) based on the building. 
 
     
     
         6 . The method of  claim 3 , wherein determining the reference angle (θ REF ) comprises:
 determining a building containing the reference wall; 
 finding the building on an overhead map; and 
 computing the reference angle (θ REF ) from the overhead map. 
 
     
     
         7 . The method of  claim 3 , wherein determining the reference angle (θ REF ) comprises:
 determining a building containing the reference wall, wherein the building is indexed in a database; 
 looking up the reference angle (θ REF ) from the database. 
 
     
     
         8 . The method of  claim 3 , wherein the wall angle is a modulo of {the reference angle (θ REF )+n*90°, 360°}, wherein n is an integer. 
     
     
         9 . The method of  claim 3 , wherein selecting the wall angle is based on inertial sensor measurements. 
     
     
         10 . A mobile device for navigation using wall matching with a horizontal feature to estimate motion, the mobile device comprising:
 a camera;   an inertial sensor; and   a processor comprising code for:
 capturing, with the camera in the mobile device, a local image containing the horizontal feature; 
 processing the local image to determine a horizontal feature angle (θ HF ), wherein the horizontal feature angle (θ HF ) is an angle from a current orientation of the mobile device to the horizontal feature; and 
 estimating a direction of motion of the mobile device, based on the horizontal feature angle (θ HF ), as parallel to a wall angle of the horizontal feature. 
   
     
     
         11 . The mobile device of  claim 10 , wherein the code further comprises code for:
 determining a reference angle (θ REF ) of a reference wall, wherein the reference angle (θ REF ) is an absolute angle with respect to North; and   selecting a wall angle, of the horizontal feature, equal to an integer multiple of 90° from the reference angle (θ REF ).   
     
     
         12 . The mobile device of  claim 11 , wherein the code for determining the reference angle (θ REF ) comprises code for computing the reference angle (θ REF ) from an overhead map. 
     
     
         13 . The mobile device of  claim 11 , wherein the code for determining the reference angle (θ REF ) comprises code for looking up the reference angle (θ REF ) from a database. 
     
     
         14 . A mobile device for navigation using wall matching with a horizontal feature to estimate motion, the mobile device comprising:
 means for capturing a local image containing the horizontal feature;   means for processing the local image to determine a horizontal feature angle (θ HF ), wherein the horizontal feature angle (θ HF ) is an angle from a current orientation of the mobile device to the horizontal feature; and   means for estimating a direction of motion of the mobile device, based on the horizontal feature angle (θ HF ), as parallel to a wall angle of the horizontal feature.   
     
     
         15 . The mobile device of  claim 14 , further comprising:
 means for determining a reference angle (θ REF ) of a reference wall, wherein the reference angle (θ REF ) is an absolute angle with respect to North; and   means for selecting a wall angle, of the horizontal feature, equal to an integer multiple of 90° from the reference angle (θ REF ).   
     
     
         16 . The mobile device of  claim 15 , wherein the means for determining the reference angle (θ REF ) comprises means for computing the reference angle (θ REF ) from an overhead map. 
     
     
         17 . The mobile device of  claim 15 , wherein the means for determining the reference angle (θ REF ) comprises means for looking up the reference angle (θ REF ) from a database. 
     
     
         18 . A non-transient computer-readable storage medium including program code stored thereon, a mobile device to navigate using wall matching with a horizontal feature to estimate motion, comprising program code for:
 receiving, from a camera in the mobile device, a local image containing the horizontal feature;   processing the local image to determine a horizontal feature angle (θ HF ), wherein the horizontal feature angle (θ HF ) is an angle from a current orientation of the mobile device to the horizontal feature; and   estimating a direction of motion of the mobile device, based on the horizontal feature angle (θ HF ), as parallel to a wall angle of the horizontal feature.   
     
     
         19 . The non-transient computer-readable storage medium of  claim 18 , wherein the program code further comprises program code for:
 determining a reference angle (θ REF ) of a reference wall, wherein the reference angle (θ REF ) is an absolute angle with respect to North; and   selecting a wall angle, of the horizontal feature, equal to an integer multiple of 90° from the reference angle (θ REF ).   
     
     
         20 . The non-transient computer-readable storage medium of  claim 19 , wherein the program code for determining the reference angle (θ REF ) comprises program code for computing the reference angle (θ REF ) from an overhead map. 
     
     
         21 . The non-transient computer-readable storage medium of  claim 19 , wherein the program code for determining the reference angle (θ REF ) comprises program code for looking up the reference angle (θ REF ) from a database.