F_VN_CalibrateCameraExp

Compute the camera parameters (intrinsic + extrinsic) by evaluating images containing a calibration pattern (circles). The extrinsic parameters are computed for the first image in the array. (expert function)
Can use available TwinCAT Job Tasks for executing parallel code regions.

Syntax

Definition:

FUNCTION F_VN_CalibrateCameraExp : HRESULT
VAR_INPUT
    pSrcImages              : PVOID;
    nSrcArraySize           : UINT;
    ipReferencePoints       : ITcVnContainer;
END_VAR
VAR_IN_OUT
    aCameraMatrix           : TcVnMatrix3x3_LREAL;
    aDistortionCoefficients : TcVnArray8_LREAL;
    aRotationMatrix         : TcVnMatrix3x3_LREAL;
    aTranslationVector      : TcVnVector3_LREAL;
    fReprojError            : LREAL;
    stBlobDetectionParams   : TcVnParamsBlobDetection;
    stCalibrationOptions    : TcVnCameraCalibrationOptions;
END_VAR
VAR_INPUT
    hrPrev                  : HRESULT;
END_VAR

Inputs

Name	Type	Description
pSrcImages	PVOID	Pointer to an array of source images, each containing the same calibration pattern (1 channel, USINT elements)
nSrcArraySize	UINT	pSrcImages array size
ipReferencePoints	ITcVnContainer	Reference calibration pattern point positions (ContainerType_Vector_TcVnPoint3_REAL)
hrPrev	HRESULT	HRESULT indicating the result of previous operations (If SUCCEEDED(hrPrev) equals false, no operation is executed.)

In/Outputs

Name	Type	Description
aCameraMatrix	TcVnMatrix3x3_LREAL	Returns the camera matrix
aDistortionCoefficients	TcVnArray8_LREAL	Returns the lens distortion coefficients [k1, k2, p1, p2, k3, k4, k5, k6]
aRotationMatrix	TcVnMatrix3x3_LREAL	Returns the rotation matrix
aTranslationVector	TcVnVector3_LREAL	Returns the translation vector
fReprojError	LREAL	Returns the reprojection error
stBlobDetectionParams	TcVnParamsBlobDetection	Parameters for the internally used F_VN_DetectBlobs function
stCalibrationOptions	TcVnCameraCalibrationOptions	Calibration options

Return value

HRESULT

Further information

The function F_VN_CalibrateCameraExp is the expert version of F_VN_CalibrateCamera. It enables the use of several input images for the calibration of the camera.

Parameter

Input images

The input images for the camera calibration are transferred to the function with the help of the pointer pSrcImages and the number of images nSrcArraySize. The individual images must otherwise meet the same requirements as for the standard function.

WARNING

Pointer handling

Make sure that the specification of the pointer and the array size match the actual data. Otherwise an impermissible memory access may occur, resulting in a system crash.

Reference points

The container ipReferencePoints must contain the reference points that are illustrated on the input image ipSrcImage as the calibration pattern. The points must be specified as 3-dimensional points of the type REAL so that the container is of the type ContainerType_Vector_TcVnPoint3_REAL.

The reference points can be generated as follows:

Manual creation of an XML file and reading with the function block FB_VN_ReadCalibrationPattern.
Configuration in the calibration assistants, saving in the TcCOM object by clicking Write Results and reading with the method GetCalibPatternRef of the function block FB_VN_GevCameraControl. The set center point is taken into account.
Inserting reference points individually into a container.

Matrices of the camera parameters

These matrices return the calculated parameters of the camera model. They can then be used for the compensation of the objective distortions and for the conversion between pixel coordinates and world coordinates.

Camera matrix
Distortion coefficients
Rotation matrix
Translation vector

	Rounding errors On account of rounding errors, the calculated parameter values can deviate slightly from the values calculated in the calibration assistants.

Reprojection errors

Parameters for blob detection

	No chessboard pattern As the reference points are detected as a blob structure, the use of chessboard patterns is not possible.

Options for calibration

	Default settings To get the default settings from the calibration wizard, the bits `bFixAspectRatio`, `bFixPrincipalPoint`, `bFixK5`, `bFixK6` and `bRationalModel` must be set to TRUE. bFixPrincipalPoint = „Fix Center Point“ The bit `bFixPrincipalPoint` corresponds to the option "Fix Center Point" in the camera calibration assistant.

Application

Samples

Calibration Assistant

Required License

TC3 Vision Metrology 2D

System Requirements

Development environment	Target platform	PLC libraries to include
TwinCAT V3.1.4024.54 or later	PC or CX (x64) with PL50, e.g. Intel 4-core Atom CPU	Tc3_Vision