Calibrating camera offsets to facilitate object position determination using triangulation

A method of determining the position of an object relative to a reference frame from captured images of the object based on multiple triangulation results, the captured images being taken by at least two pair of cameras having fields of view encompassing the reference frame, an extremity of the field of view of each camera encompassing a boundary of said reference frame, at least one of said cameras being offset causing the extremity of the field of view thereof to extend beyond said boundary, the offset defining an offset angle, said method comprising the steps of:

• determining the position of the object within each image, the position of the object within each image being represented by an angle, said angle being equal to the angle formed between the extremity of the field of view of the camera that acquired the image and a line extending from that camera that intersects the object within the image;
• determining the offset angle for each offset camera;
• for each offset camera subtracting the offset angle from the angle representing the position of the object within the image taken by said offset camera to calibrate the angle;
• and
• for each pair of cameras using the calibrated angles to calculate the position of the object with respect to the reference frame using triangulation.

In a touch system including at least two pair of cameras and a processor to process images acquired by said at least two pair cameras, where the position of an object that is within the fields of view of said cameras relative to a reference frame is determined by triangulating object position data in images acquired by the cameras of each pair, a method of calibrating the touch system comprising the steps of:

• determining an offset angle of each camera relative to the reference frame, said offset angle representing the degree by which the field of view of the camera extends beyond said reference frame;
• for each camera, using the offset angle to calibrate the object position data developed from the image acquired by that camera;
• and
• using the calibrated object position data during triangulation for each pair of cameras to determine the position of said object relative to said reference frame.

In a touch system including a reference frame, and at least two pair of cameras having fields of view that encompass said reference frame, wherein the position of an object relative to the reference frame is determined from captured images of the object based on multiple triangulation results, and wherein the fields of view of at least some of said cameras are rotated with respect to the coordinate system of said reference frame to define offset angles, a method of calibrating said touch system comprising the steps of:

• capturing an image of the object using each camera of said at least two pair at at least one location within said reference frame;
• and
• for each location:
• determining the position of the object within each captured image, the position of the object within each captured image being represented by an angle φ, said angle being equal to the angle formed between an extremity of the field of view of the camera that acquired the image extending beyond the reference frame and a line extending from that camera that intersects the object within the image;
• and
• mathematically calculating the offset angles of the cameras having rotated fields of view based on the angle determined for each image and the position of the cameras relative to the coordinate system assigned to said reference frame.

A touch system comprising:

• a generally rectangular reference frame surrounding a touch surface, one corner of the reference frame defining the origin of a coordinate system assigned to said touch surface;
• a camera adjacent each corner of the reference frame, each camera being aimed towards said touch surface and capturing images of said touch surface within the field of view thereof, fields of view of said cameras overlapping within said reference frame, the fields of view of said cameras being offset with respect to said reference frame;
• and
• a processor processing the captured images and generating object position data when an object appears in images, said processor determining the position of said object relative to said origin in rectangular coordinates using said object position data based on multiple triangulation results, wherein said processor further executes a calibration routine to determine offset angles of said cameras, said offset angles being used by said processor to adjust said object position data thereby to align said multiple triangulation results prior to said position determination.

A touch system comprising:

• a substantially rectangular touch surface;
• imaging devices mounted adjacent at least three corners of said touch surface to define at least two triangulation pair of imaging devices, each imaging device having a field of view looking across said touch surface, said imaging devices being oriented to capture overlapping images of said touch surface;
• and
• at least one processing device processing captured images to determine the position of at least one pointer appearing in the captured images based on multiple triangular results, the fields of view of said imaging devices being calibrated by said at least one processing device to determine offset angles of said imaging devices prior to determining the position of the at least one pointer thereby to align said multiple triangulation results.