F_VN_MeasureMinEdgeDistanceExp

Syntax

Definition:

FUNCTION F_VN_MeasureMinEdgeDistanceExp : HRESULT
VAR_INPUT
    ipSrcImage             : ITcVnImage;
END_VAR
VAR_IN_OUT
    fMinDistance           : REAL;
    aStartPoint            : TcVnPoint2_REAL;
    aEndPoint              : TcVnPoint2_REAL;
END_VAR
VAR_INPUT
    eEdgeDirection         : ETcVnEdgeDirection;
    fMinStrength           : REAL;
    nSearchLines           : UDINT;
    fSearchLineDist        : REAL;
    nMaxThickness          : UDINT;
    bInvertSearchDirection : BOOL;
    fSearchGap             : REAL;
    nSubpixelsIterations   : UDINT;
    fApproxPrecision       : REAL;
    eAlgorithm             : ETcVnEdgeDetectionAlgorithm;
    ipEdgePoints1          : Reference To  ITcVnContainer;
    ipEdgePoints2          : Reference To  ITcVnContainer;
END_VAR
VAR_IN_OUT
    aPoint1                : TcVnPoint2_REAL;
    aPoint2                : TcVnPoint2_REAL;
END_VAR
VAR_INPUT
    hrPrev                 : HRESULT;
END_VAR

Inputs

Name	Type	Description
ipSrcImage	ITcVnImage	Source image (1 channel)
eEdgeDirection	ETcVnEdgeDirection	Specification of the edge direction from aStartPoint to aEndPoint to search 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
bInvertSearchDirection	BOOL	If true, the search starts from the center point between aStartPoint and aEndPoint in both directions
fSearchGap	REAL	Optional width of a gap (>= 0, centered between aStartPoint and aEndPoint), that is neglected for searching edges (can reduce execution time). The 2 edges to search for must be on different sides of the gap.
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
ipEdgePoints1	Reference To ITcVnContainer	Returns the detected edge points of the edge near aStartPoint (optional, set to 0 if not required; ContainerType_Vector_TcVnPoint2_REAL)
ipEdgePoints2	Reference To ITcVnContainer	Returns the detected edge points of the edge near aEndPoint (optional, set to 0 if not required; ContainerType_Vector_TcVnPoint2_REAL)
hrPrev	HRESULT	HRESULT indicating the result of previous operations (If SUCCEEDED(hrPrev) equals false, no operation is executed.)

In/Outputs

Name	Type	Description
fMinDistance	REAL	Returns the minimum distance between the detected edges
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
aPoint1	TcVnPoint2_REAL	Returns the point on the edge near aStartPoint, for which the minimum distance is achieved
aPoint2	TcVnPoint2_REAL	Returns the point on the edge near aEndPoint, for which the minimum distance is achieved

Return value

HRESULT

Further information

The function F_VN_MeasureMinEdgeDistanceExp is the expert version of F_VN_MeasureMinEdgeDistance. It contains additional parameters.

Parameter

Input image

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

Minimum distance ^{(Return value)}

The parameter fMinDistance returns the minimum distance between the two localized edges.

Localized edge points ^{(Return value)}

The containers ipEdgePoints1 and ipEdgePoints2 return the exact points that were localized on the basis of each search line. If not needed, the value 0 can be transferred instead of an interface pointer.

In addition, the points aPoint1 and aPoint2 return the points that have the minimum distance between the two edges.

Search gap ^(Expert)

Area in the center of the defined search line in which the search is omitted. The execution time can be reduced as a result.

Parameters for edge localization

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

Application

The measurement of the minimum edge distance with expert parameters looks like this, for example:

hr := F_VN_MeasureEdgeDistance(
    ipSrcImage              :=  ipImageIn, 
    fMinDistance            :=  fDistance
    aStartPoint             :=  aStartPoint, 
    aEndPoint               :=  aEndPoint,
    eEdgeDirection          :=  TCVN_ED_LIGHT_TO_DARK,
    fMinStrength            :=  fMinStrength, 
    nSearchLines            :=  nSearchLines,
    fSearchLineDist         :=  3
    nMaxThickness           :=  7,
    bInvertSearchDirection  :=  TRUE,
    nSubpixelsIterations    :=  100,
    fApproxPrecision        :=  0.0001,
    eAlgorithm              :=  TCVN_EDA_APPROX_ERF,
    ipEdgePoints1           :=  ipEdge1, 
    ipEdgePoints2           :=  ipEdge2, 
    aPoint1                 :=  aPoint1, 
    aPoint2                 :=  aPoint2,
    hrPrev                  :=  hr
);

The localized edge points can be visualized with the functions F_VN_DrawContours and F_VN_DrawPoint:

hr := F_VN_DrawContours(ipEdgePoints1, -1, ipImageRes, aColorGreen, 5, hr);
hr := F_VN_DrawContours(ipEdgePoints2, -1, ipImageRes, aColorGreen, 5, hr);

F_VN_DrawPoint(aPoint1[0], aPoint1[1], ipImageRes, TCVN_DS_X, aColorGreen, hr);
F_VN_DrawPoint(aPoint2[0], aPoint2[1], ipImageRes, TCVN_DS_X, aColorGreen, hr);

Related functions

ClosestPointsBF for calculating the closest points in two point clouds
MeasureAngleBetweenEdges for measuring the angle between two edges
MeasureEdgeDistance for measuring the average distance between two edges
MeasureMinEdgeDistance for measuring the minimum distance between two edges

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