Pivot point calibration. More...
#include <PivotCalibration.hpp>
Public Types | |
typedef T | value_type |
typedef super::Vector3T | Vector3T |
typedef super::Vector4T | Vector4T |
typedef super::VectorXT | VectorXT |
typedef super::Matrix3T | Matrix3T |
typedef super::MatrixXT | MatrixXT |
typedef super::Point | Point |
typedef super::DataType | DataType |
enum | Error { NOT_ENOUGH_INPUT_DATA, UNEQUAL_CARDINALITY_OF_INPUT_SETS, UNKNOWN_ERROR } |
typedef Eigen::Matrix< T, 4, 4 > | Matrix4T |
Public Member Functions | |
size_t | getNumberItemsRequired () const |
Returns the minimum number of locations and rotations needed for the algorithm. | |
void | setLocations (Range< Vector3T > locations) |
void | setRotations (Range< Matrix3T > rotations) |
T | compute () |
Returns the RMSE. | |
T | getRMSE () const |
Returns the RMSE of the last computation. | |
const Vector3T & | getPivotPoint () const |
Returns the pivot point (or tool tip) in world coordinates. | |
const Vector3T & | getLocalPivotPoint () const |
Returns the pivot point (or tool tip) in local coordinates. |
Pivot point calibration.
T | scalar (floating point) type |
This class estimates the pivot point of a rigid body whose movement is constrained to rotate around a certain pivot point and whose movement is tracked via a localization system. Typical examples of application include the tool tip calibration or the hip center determination.
The calibration procedure to obtain a tool tip location is as follows: The tool tip is placed in a divot and the tool is moved around this pivot point while always touching the divot with its tip. The location as well as the rotation of the sensor system is saved for each sampling instance. Then this list is passed to one of the pivot calibration algorithms and the sought location/translation is computed.
Movement of a tool while recording data for the tool tip calibration.
Given a new measurement of the tracker (which comprises the position \( t_i \) and orientation \( R_i \) of the sensor in the global coordinate system) the pivot point the tool tip location in global coordinates can be easily computed as \( p_{global} = R_i p_{local} + t_i \).
During the calibration procedure, the object's sensor moves along a circular arc (or in three dimensions on a calotte of a sphere). In a first step, the center point (= pivot point) as well as the radius of this sphere are estimated by a simple least square scheme (that's done in global coordinates). See TRTK::FitSphere for more details.
Provided the object is positioned as described above (e.g. the tool tip is stationary), using a single measurement \( (R_i, t_i) \) the global pivot point \( p' \) can be easily transformed into a local coordinate \( p \) via the relation
\[ p' = R p + t \quad\quad \Leftrightarrow \quad\quad p = R^{-1} (p' - t) \]
where \( R \) is the rotation and \( t \) the location of the sensor in the global coordinate system. However, due to noise, various results for \( p \) are averaged. Instead of recording a new set of pairs of \( (R_i, t_i) \) after having determined the virtual sphere, the former measurements are used.
For some example code please be referred to PivotCalibration.
Definition at line 1219 of file PivotCalibration.hpp.
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