LocateCircularArc

Locate a circular arc.
Can use available TwinCAT Job Tasks for executing parallel code regions.
Can return partial results when canceled by Watchdog.

Syntax

Definition:

HRESULT LocateCircularArc(
    HRESULT                     hrPrev,
    ITcVnImage*                 ipSrcImage,
    TcVnCircularArc&            stCircularArc,
    TcVnPoint2_REAL&            aCenter,
    float                       fSearchRadius,
    double                      fArcDirectionRad,
    ETcVnEdgeDirection          eEdgeDirection,
    float                       fMinStrength,
    double                      fAngleStepRad = 0.1,
    ULONG                       nMaxThickness = 10,
    bool                        bInvertSearchDirection = false,
    ULONG                       nSubpixelsIterations = 10,
    float                       fApproxPrecision = 0.001f,
    ETcVnEdgeDetectionAlgorithm eAlgorithm = EDA_INTERPOLATION,
    ITcVnContainer**            pipContourPoints = 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)

stCircularArc

TcVnCircularArc&

 

Returns the circular arc parameters

aCenter

TcVnPoint2_REAL&

 

Input estimated circle center (only used as a starting point to search for the circle contour, not used for the circle center estimation)

fSearchRadius

float

 

Input search radius (starting from aCenter, should be greater than the actual circle radius but aCenter + fSearchRadius should be within the image borders)

fArcDirectionRad

double

 

Input search starting direction in radian. Valid range is [-pi, +pi], where right is 0 rad, top is -pi/2 rad and bottom +pi/2 rad. The circular arc should at least be valid in range fArcDirectionRad +- 4 * fAngleStepRad)

eEdgeDirection

ETcVnEdgeDirection

 

Specification of the edge direction to search for

fMinStrength

float

 

Specification of the minimum strength (intensity difference) of the edge to search for

fAngleStepRad

double

0.1

Search step in rad (should be chosen so that about 20 - 60 steps are available for the whole arc. In most cases 0.1 rad (5.7 deg) is a good value)

nMaxThickness

ULONG

10

Specification of the maximum thickness of the edge to search for, which means fMinStrength must be reached within nMaxThickness pixels

bInvertSearchDirection

bool

false

If true, the search starts from outside the circular arc in direction of the center

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

pipContourPoints

ITcVnContainer**

nullptr

Returns the subpixel accurate contour (optional, set to 0 if not required; ContainerType_Vector_TcVnPoint2_REAL; Non-zero interface pointers are reused.)

LocateCircularArc 1: Return value

HRESULT

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