Method and Device for Calibrating a 3D TOF Camera System

• US 20120206575A1
• Filed: 04/19/2012
• Published: 08/16/2012
• Est. Priority Date: 10/28/2009
• Status: Active Grant

• Current Assignee: ifm electronic GmbH (ifm stiftung & Co. KG)
• Original Assignee: ifm electronic GmbH (ifm stiftung & Co. KG)
• Inventors: Frey, Volker, May, Thomas, Massanell, Javier
• Granted Patent: US 9,726,754 B2
• Time in Patent Office: Days
• US Class Current: 348/46
• CPC Class Codes: G01S 17/36 with phase comparison between the received signal and the contemporaneously transmitted signal
• CPC Class Codes: G01S 17/931 of land vehicles
• CPC Class Codes: G01S 7/4972 Alignment of sensor

Abstract

A method for calibrating a three dimensional time-of-flight camera system mounted on a device, includes determining at a first instant a direction vector relating to an object; determining an expected direction vector and expected angle for the object to be measured at a second instant with reference to the device'"'"'s assumed trajectory and optical axis of the camera; determining a current direction vector and current angle at the second instant; determining an error represented by a difference between the current direction vector and the expected direction vector; and using the error to correct the assumed direction of the main optical axis of the camera system such that said error is substantially eliminated.

Claims

1. A method for calibrating a three dimensional time-of-flight camera system mounted on a moveable device, comprising the steps of:

detecting and identifying at least one object to be measured (MO, MO1/2);

determining at a first instant a direction vector (d₁) relating to at the least one object to be measured (MO, MO1/2);

determining an expected direction vector (d_1E) and an expected angle (α

_1E) for the object to be measured that are expected at a second instant (t′

) later than the first instant with reference to an assumed trajectory (TR′

) of the device and an assumed direction of the main optical axis HA of the camera system;

detecting the object to be measured (MO, MO1, MO2) at the second instant (t′

) and determining a current direction vector (d_1T) and current angle (α

_1T) with reference to the assumed trajectory (TR′

) of the device and assumed direction of the main optical axis HA of the camera system;

determining an error represented by a difference between the current direction vector (d_1T) and the expected direction vector (d_1E); and

using the error to correct the assumed direction of the main optical axis of the camera system such that said error is substantially eliminated.

2. The method of claim 1 wherein an error signal is produced as a function of the magnitude of the vector difference.

3. The method of claim 1 wherein said error is used to automatically correct the assumed direction of the main optical axis of the camera system such that said difference is substantially eliminated.

4. A method for calibrating a three dimensional time-of-flight camera system mounted on a moveable device, comprising the steps of:

detecting and identifying at least two objects to be measured (MO1, MO2), each object being spaced from the other object by a known distance;

determining at a first instant (t) a first set of direction vectors (d1, d2) relating to the two objects to be measured (MO1, MO2);

determining expected direction vectors (d_1E, d_2E) for the two objects to be measured (MO1, MO2) that are expected at a second instant (t′

) later than the first instant with reference to an assumed trajectory (TR′

) of the device and an assumed direction of the main optical axis HA of the camera system;

detecting the objects to be measured (MO1, MO2) at the second instant (t′

), and determining a second set of current direction vectors (d_1T, d_2T) with reference to the assumed trajectory (TR′

) of the device and the assumed direction of the main optical axis HA of the camera system;

determining an error represented by respective differences between the current direction vectors (d_1E, d_2E) and the expected direction vectors (d_IT, d_2T); and

using the error to correct the assumed direction of the main optical axis of the camera system such that said error is substantially eliminated.

5. The method of claim 4 wherein an error signal is produced as a function of the magnitude of the vector difference.

6. The method of claim 4 wherein said error is used to automatically correct the assumed direction of the main optical axis of the camera system such that said difference is substantially eliminated.

7. A method for calibrating a three dimensional time-of-flight camera system mounted on a moveable device, comprising the steps of:

detecting and identifying two objects to be measured (MO1, MO2), each object being spaced from the other object by a known distance d₁₂;

determining a set of direction vectors (d1, d2) and angles (α

₁, α

₂) relating to the two objects to be measured (MO1, MO2) with reference to an assumed direction of the main optical axis HA of the camera system;

using the set of direction vectors (d1, d2) and angles (α

₁, α

₂) to determine an indicated distance between the two objects to be measured (MO1, MO2);

determining an error represented by a difference between the known distance d₁₂ and the indicated distance; and

using the error to correct the assumed direction of the main optical axis of the camera system such that said error is substantially eliminated.

8. The method of claim 7 wherein an error signal is produced as a function of the magnitude of the difference between the known distance d₁₂ and the indicated distance.

9. The method of claim 7 wherein said error is used to automatically correct the assumed direction of the main optical axis of the camera system such that said difference between the known distance d₁₂ and the indicated distance is substantially eliminated.

10. A three dimensional time-of-flight camera system able to be mounted on a moveable device and adapted to execute the steps of:

detecting and identifying at least one object to be measured (MO, MO1/2);

determining at a first instant a direction vector (d₁) relating to at the least one object to be measured (MO, MO1/2);

determining an expected direction vector (d_1E) and an expected angle (α

_1E) for the object to be measured that are expected at a second instant (t′

) later than the first instant with reference to an assumed trajectory (TR′

) of the device and an assumed direction of the main optical axis HA of the camera system;

detecting the object to be measured (MO, MO1, MO2) at the second instant (t′

) and determining a current direction vector (d_1T) and current angle (α

_1T) with reference to the assumed trajectory (TR′

) of the device and assumed direction of the main optical axis HA of the camera system;

determining an error represented by a difference between the current direction vector (d_1T) and the expected direction vector (d_1E); and

using the error to correct the assumed direction of the main optical axis of the camera system such that said error is substantially eliminated.