LocateEdges

Locate the points of multiple occuring edges inside a specified search window with subpixel accuracy.
Can use available TwinCAT Job Tasks for executing parallel code regions.
Can return partial results when canceled by Watchdog.

Syntax

Definition:

HRESULT LocateEdges(
    HRESULT                     hrPrev,
    ITcVnImage*                 ipSrcImage,
    ITcVnContainer*&            ipEdgePoints,
    TcVnPoint2_REAL&            aStartPoint,
    TcVnPoint2_REAL&            aEndPoint,
    ULONG                       nNumEdges,
    ETcVnEdgeDirection          eEdgeDirection,
    bool                        bAlternateDirection,
    float                       fMinStrength,
    ULONG                       nSearchLines,
    float&                      fAvgStrength,
    float                       fSearchLineDist = 1,
    ULONG                       nMaxThickness = 10,
    ULONG                       nSubpixelsIterations = 10,
    float                       fApproxPrecision = 0.001f,
    ETcVnEdgeDetectionAlgorithm eAlgorithm = EDA_INTERPOLATION,
    float                       fRangeCutoffFactor = 0.135f,
    ITcVnContainer**            pipEdgeStrengths = nullptr,
    bool                        bAvgEdgeStrengths = false
)

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)
ipEdgePoints	ITcVnContainer*&		Returns the detected edge points (ContainerType_Vector_Vector_TcVnPoint2_REAL)
aStartPoint	TcVnPoint2_REAL&		Position from which to start the search process (in the direction of aEndPoint)
aEndPoint	TcVnPoint2_REAL&		Position where the search process ends
nNumEdges	ULONG		The (maximum) number of edges to search for
eEdgeDirection	ETcVnEdgeDirection		Specification of the edge direction to search for
bAlternateDirection	bool		If true, eEdgeDirection is alternated after each detected edge. Else, only edges with eEdgeDirection are searched for.
fMinStrength	float		Specification of the minimum strength (intensity difference) of the edge to search for
nSearchLines	ULONG		Width of the search window, i.e. the number of search lines (1, 3, 5, 7, ...), centered around the line specified by aStartPoint and aEndPoint
fAvgStrength	float&		Returns the average strength of the detected edges
fSearchLineDist	float	1	Distance between the search lines in pixels (> 0)
nMaxThickness	ULONG	10	Specification of the maximum thickness of the edge to search for, which means fMinStrength must be reached within nMaxThickness pixels
nSubpixelsIterations	ULONG	10	Specifies the number of subpixels (for INTERPOLATION, 10 - 20 usually is sufficient) or maximum number of iterations for optimizing the parameters (for APPROX_ERF and APPROX_GAUSSIAN, 50 - 100 usually is sufficient)
fApproxPrecision	float	0.001f	Specifies the approximation precision for APPROX_ERF and APPROX_GAUSSIAN (0.001 usually is sufficient, unused for INTERPOLATION)
eAlgorithm	ETcVnEdgeDetectionAlgorithm	EDA_INTERPOLATION	Selection of the edge detection algorithm
fRangeCutoffFactor	float	0.135f	Relative edge strength factor to cut off the range of pixels used for approximation. Negative numbers are valid to include noise, i.e. intensity differences in the other direction. At most nMaxThickness pixels are used in each direction.
pipEdgeStrengths	ITcVnContainer**	nullptr	Returns the detected edge strengths (optional, set to 0 if not required; ContainerType_Vector_Vector_REAL or ContainerType_Vector_REAL, depending on bAvgEdgeStrengths)
bAvgEdgeStrengths	bool	false	If true, ipEdgeStrengths returns the average strength per edge instead of individual strengths for each search line

Return value

HRESULT

Required License

TC3 Vision Metrology 2D

System Requirements

Development environment	Target platform	PLC libraries to include
TwinCAT V3.1.4024.59 or later	PC or CX (x64) with min. PL50, e.g. Intel 4-core Atom CPU	Tc3_Vision