F_VN_MeasureAngleBetweenEdgesExp

F_VN_MeasureAngleBetweenEdgesExp 1:

Measure the angle between 2 edges.
Can use available TwinCAT Job Tasks for executing parallel code regions.
Can return partial results when canceled by Watchdog.

Syntax

Definition:

FUNCTION F_VN_MeasureAngleBetweenEdgesExp : HRESULT
VAR_INPUT
    ipSrcImage             : ITcVnImage;
END_VAR
VAR_IN_OUT
    fAngle                 : REAL;
    aInnerPoint            : TcVnPoint2_REAL;
    aOuterPoint1           : TcVnPoint2_REAL;
    aOuterPoint2           : TcVnPoint2_REAL;
END_VAR
VAR_INPUT
    eEdgeDirection         : ETcVnEdgeDirection;
    fMinStrength           : REAL;
    nSearchLines           : UDINT;
    fSearchLineDist        : REAL;
    nMaxThickness          : UDINT;
    bInvertSearchDirection : BOOL;
    nSubpixelsIterations   : UDINT;
    bAngleInDegrees        : BOOL;
    fApproxPrecision       : REAL;
    eAlgorithm             : ETcVnEdgeDetectionAlgorithm;
    ipEdgePoints1          : Reference To ITcVnContainer;
    ipEdgePoints2          : Reference To ITcVnContainer;
    hrPrev                 : HRESULT;
END_VAR

F_VN_MeasureAngleBetweenEdgesExp 2: Inputs

Name

Type

Description

ipSrcImage

ITcVnImage

Source image (1 channel)

eEdgeDirection

ETcVnEdgeDirection

Specification of the edge direction from aInnerPoint to aOuterPoint1 and aOuterPoint2 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 (3, 5, 7, ...), centered around the line specified by aInnerPoint and aOuterPoint1, aOuterPoint2

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 each aOuterPoint in direction of aInnerPoint

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)

bAngleInDegrees

BOOL

fAngle is in degrees, if true

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 between aInnerPoint and aOuterPoint1 (ContainerType_Vector_TcVnPoint2_REAL)

ipEdgePoints2

Reference To ITcVnContainer

Returns the detected edge points between aInnerPoint and aOuterPoint2 (ContainerType_Vector_TcVnPoint2_REAL)

hrPrev

HRESULT

HRESULT indicating the result of previous operations (If SUCCEEDED(hrPrev) equals false, no operation is executed.)

F_VN_MeasureAngleBetweenEdgesExp 3: In/Outputs

Name

Type

Description

fAngle

REAL

Returns the angle between the detected edges (radians or degrees, depending on bAngleInDegrees)

aInnerPoint

TcVnPoint2_REAL

Position inside the angle to measure, from which to start the edge search process (in the direction of aOuterPoint1 and aOuterPoint2)

aOuterPoint1

TcVnPoint2_REAL

Position where the search process for edge 1 ends

aOuterPoint2

TcVnPoint2_REAL

Position where the search process for edge 2 ends

F_VN_MeasureAngleBetweenEdgesExp 4: Return value

HRESULT

Further information

The function F_VN_MeasureAngleBetweenEdgesExp is the expert function of F_VN_MeasureAngleBetweenEdges.

Parameter

Input image

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

Angle (Return value)

The parameter fAngle returns the angle between the localized edges.

Depending on the parameter bAngleInDegrees, the angle fAngle is specified in radians (FALSE) or in degrees (TRUE).

Parameters for edge localization

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

Localized points (Expert, 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

Parameters for edge localization

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

Application

The measurement of an angle with expert parameters looks like this, for example:

hr := F_VN_MeasureAngleBetweenEdgesExp(
    ipSrcImage             :=   ipImageIn,
    fAngle                 :=   fAngle
    aInnerPoint            :=   aInnerPoint,
    aOuterPoint1           :=   aOuterPoint1
    aOuterPoint2           :=   aOuterPoint2,
    eEdgeDirection         :=   TCVN_ED_LIGHT_TO_DARK,
    fMinStrength           :=   fMinStrength,
    nSearchLines           :=   nSearchLines,
    fSearchLineDist        :=   fSearchLineDist,
    nMaxThickness          :=   7,
    nSubpixelsIterations   :=   100,
    bAngleInDegrees        :=   TRUE,
    fApproxPrecision       :=   0.0001,
    eAlgorithm             :=   TCVN_EDA_APPROX_ERF,
    ipEdgePoints1          :=   ipEdgePoints1,
    ipEdgePoints2          :=   ipEdgePoints2,

    hrPrev                 :=   hr
);

Samples

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