F_VN_MeasureMinEdgeDistanceExp
Measure the minimum distance within the specified search window between 2 edges. (expert function)
Can use available TwinCAT Job Tasks for executing parallel code regions.
Can return partial results when canceled by Watchdog.
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 |
Source image (1 channel) | |
|
eEdgeDirection |
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 |
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 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 |
Position from which to start the search process (in the direction of aEndPoint) | |
|
aEndPoint |
Position where the search process ends | |
|
aPoint1 |
Returns the point on the edge near aStartPoint, for which the minimum distance is achieved | |
|
aPoint2 |
Returns the point on the edge near aEndPoint, for which the minimum distance is achieved |
Return valueFurther 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. This can reduce the execution time.
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 V3.1.4024.59 or later | PC or CX (x64) with PL50, e.g. Intel 4-core Atom CPU | Tc3_Vision |