LocateAxisAlignedEdges

Locate the position of multiple occurring edges inside a specified search window. The edges inside the search window must be straight and aligned to one of the image axes. They are located by interpolating the peaks of the first Gaussian derivative of the pixel intensities.

Syntax

Definition:

HRESULT LocateAxisAlignedEdges(
    HRESULT            hrPrev,
    ITcVnImage*        ipSrcImage,
    ITcVnContainer*&   ipEdgePoints,
    TcVnPoint2_DINT&   aStartPoint,
    TcVnPoint2_DINT&   aEndPoint,
    ULONG              nSearchWindowHeight,
    ULONG              nKernelSize,
    ULONG              nNumEdges,
    ETcVnEdgeSelection eEdgeSelection,
    float              fMinStrength,
    float&             fAvgStrength,
    float              fSigma = 0,
    ITcVnContainer**   pipEdgeStrengths = nullptr,
    ITcVnImage**       pipDerivative = nullptr
)

Parameters

Name	Type	Default	Description
hrPrev	HRESULT		HRESULT indicating the result of previous operations (If SUCCEEDED(hrPrev) equals false, no operation is executed.)
ipSrcImage	ITcVnImage*		Source image (1 channel of type ET_USINT, ET_UINT, ET_INT or ET_REAL)
ipEdgePoints	ITcVnContainer*&		Returns the detected edge points (ContainerType_Vector_TcVnPoint2_REAL)
aStartPoint	TcVnPoint2_DINT&		Position from which to start the search process (in the direction of aEndPoint)
aEndPoint	TcVnPoint2_DINT&		Position where the search process ends. As the search direction must be parallel to one of the images axes, aEndPoint must have the same x- or y-coordinate as aStartPoint.
nSearchWindowHeight	ULONG		Specifies the height of the search window, i.e. the number of rows for horizontal or columns for vertical search directions, centered around the line between aStartPoint and aEndPoint. Depending on the orientation, the rows or columns inside that window are averaged and the edges are located on that averaged row or column. Therefore it is important that the edges inside the defined search window are straight and perpendicular to the search direction.
nKernelSize	ULONG		The size of the Gaussian derivative kernel, that is used to locate the edges. The size must be odd and >= 3 (5 or 7 are usually a good choice for sharp edges).
nNumEdges	ULONG		The (maximum) number of edges to search for
eEdgeSelection	ETcVnEdgeSelection		Selects the edge directions to search for
fMinStrength	float		Specification of the minimum strength (absolute peak height of the Gaussian derivative of the pixel intensities) of the edge to search for. This value depends on the edge sharpness and nKernelSize, but is generally smaller or equal to the difference of the pixel intensities of the edge. Sharp edges have a higher peak than unsharp ones. Initially, you might choose a relatively small value (e.g. 30) and then increase it depending on the fAvgStrength and ipEdgeStrengths output.
fAvgStrength	float&		Returns the average strength of the detected edges
fSigma	float	0	The sigma parameter for the Gaussian derivative function. If set to 0, a suitable value is automatically chosen depending on nKernelSize. For manually defined sigma, the value should always be chosen depending on nKernelSize (e.g. fSigma = (nKernelSize - 1) / factor, with factor in a range of 4 to 8).
pipEdgeStrengths	ITcVnContainer**	nullptr	Returns the individual edge strengths, where dark to light edge strengths are positive and light to dark edge strengths are negative (optional, set to 0 if not required; ContainerType_Vector_REAL).
pipDerivative	ITcVnImage**	nullptr	Returns the Gaussian derivative of the pixel intensities on the search line between aStartPoint and aEndPoint as a single image row, where aStartPoint would be on the left and aEndPoint on the right (optional, set to 0 if not required; 1 channel, ET_REAL).

Return value

HRESULT

Required License

TC3 Vision Metrology 2D

System Requirements

Development environment	Target platform	PLC libraries to include
TwinCAT V3.1.4026 or later	PC or CX (x64) with min. PL50, e.g. Intel 4-core Atom CPU	Tc3_Vision