F_VN_LocateEdgesExp

Syntax

Definition:

FUNCTION F_VN_LocateEdgesExp : HRESULT
VAR_INPUT
    ipSrcImage           : ITcVnImage;
    ipEdgePoints         : Reference To  ITcVnContainer;
END_VAR
VAR_IN_OUT
    aStartPoint          : TcVnPoint2_REAL;
    aEndPoint            : TcVnPoint2_REAL;
END_VAR
VAR_INPUT
    nNumEdges            : UDINT;
    eEdgeDirection       : ETcVnEdgeDirection;
    bAlternateDirection  : BOOL;
    fMinStrength         : REAL;
    nSearchLines         : UDINT;
    fSearchLineDist      : REAL;
    nMaxThickness        : UDINT;
    nSubpixelsIterations : UDINT;
    fApproxPrecision     : REAL;
    eAlgorithm           : ETcVnEdgeDetectionAlgorithm;
    hrPrev               : HRESULT;
END_VAR
VAR_OUTPUT
    fAvgStrength         : REAL;
END_VAR

Inputs

Name	Type	Description
ipSrcImage	ITcVnImage	Source image (1 channel)
ipEdgePoints	Reference To ITcVnContainer	Returns the detected edge points (ContainerType_Vector_Vector_TcVnPoint2_REAL)
nNumEdges	UDINT	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	REAL	Specification of the minimum strength (intensity difference) of the edge to search for
nSearchLines	UDINT	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
fSearchLineDist	REAL	Distance between the search lines in pixels (> 0)
nMaxThickness	UDINT	Specification of the maximum thickness of the edge to search for, which means fMinStrength must be reached within nMaxThickness pixels
nSubpixelsIterations	UDINT	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	REAL	Specifies the approximation precision for APPROX_ERF and APPROX_GAUSSIAN (0.001 usually is sufficient, unused for INTERPOLATION)
eAlgorithm	ETcVnEdgeDetectionAlgorithm	Selection of the edge detection algorithm
hrPrev	HRESULT	HRESULT indicating the result of previous operations (If SUCCEEDED(hrPrev) equals false, no operation is executed.)

In/Outputs

Name	Type	Description
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

Outputs

Name	Type	Description
fAvgStrength	REAL	Returns the average strength of the detected edges

Return value

HRESULT

Further information

The function F_VN_LocateEdgesExp is the expert version of F_VN_LocateEdges. It contains additional parameters.

Parameter

Input image

The input image ipSrcImage must be a 1-channel grayscale image.

Localized points ^{(Return value)}

The container ipEdgePoints returns the localized points of the linear edges.

The search window

First, a search window has to be defined to determine where and in which direction to search for an edge. This is done with the parameters aStartPoint, aEndPoint and nSearchLines. The search window results from the search line from aStartPoint to aEndPoint and parallel to it (nSearchLines - 1) / 2 search lines in each direction, each with 1 pixel distance. Thus nSearchLines defines the number of search lines and must always have an odd value.

F_VN_LocateEdgesExp 6: — S: StartPoint, E: EndPoint, W: WindowWidth

Edge strength ^{(Return value)}

The return value fAvgStrength displays the actual contrast of the localized edges (averaged over all search lines).

Parameters for edge localization

The remaining parameters are explained in detail in the chapter Edge localization.

Application

The localization of a linear edge with expert parameters looks like this, for example:

hr := F_VN_LocateEdgesExp(
    ipSrcImage              :=  ipImageIn,
    ipEdgePoints            :=  ipEdgePoints,
    aStartPoint             :=  aStartPoint,
    aEndPoint               :=  aEndPoint,
    nNumEdges               :=  nNumEdges,
    eEdgeDirection          :=  eDirection,
    bAlternateDirection     :=  bAlternateDirection,
    fMinStrength            :=  fMinStrength,
    nSearchLines            :=  nSearchLines,
    fSearchLineDist         :=  fSearchLineDist
    nMaxThickness           :=  nMaxThickness,
    nSubpixelsIterations    :=  nSubpixIter,
    fApproxPrecision        :=  0.001,
    eAlgorithm              :=  eAlgorithm,
    hrPrev                  :=  hr,
    fAvgStrength            =>  fAvgStrength
);

Related functions

LocateCircularArc for localizing proportional circular arcs
LocateEdge for localizing linear edges
LocateEdges for localizing several linear edges
LocateEllipse for localizing complete ellipses

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