F_VN_LocateEdges
Locate the points of multiple occuring edges inside a specified search window, using an interpolation method.
Can use available TwinCAT Job Tasks for executing parallel code regions.
Can return partial results when canceled by Watchdog.
Syntax
Definition:
FUNCTION F_VN_LocateEdges : 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;
hrPrev : HRESULT;
END_VAR
VAR_OUTPUT
fAvgStrength : REAL;
END_VAR
Inputs
|
Name |
Type |
Description |
|---|---|---|
|
ipSrcImage |
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 |
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 |
|
hrPrev |
HRESULT indicating the result of previous operations (If SUCCEEDED(hrPrev) equals false, no operation is executed.) |
In/Outputs
|
Name |
Type |
Description |
|---|---|---|
|
aStartPoint |
Position from which to start the search process (in the direction of aEndPoint) | |
|
aEndPoint |
Position where the search process ends |
Outputs
|
Name |
Type |
Description |
|---|---|---|
|
fAvgStrength |
REAL |
Returns the average strength of the detected edges |
Further information
The function F_VN_LocateEdges localizes several edges in a defined search window.
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.
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.
Expert parameters
The expert version F_VN_LocateEdgeExp contains additional parameters.
Application
The localization of a linear edge looks like this, for example:
hr := F_VN_LocateEdges(
ipSrcImage := ipImageIn,
ipEdgePoints := ipEdgePoints,
aStartPoint := aStartPoint,
aEndPoint := aEndPoint,
nNumEdges := nNumEdges,
eEdgeDirection := eDirection,
bAlternateDirection := bAlternateDirection,
fMinStrength := fMinStrength,
nSearchLines := nSearchLines,
hrPrev := hr,
fAvgStrength => fAvgStrength
);
The localized edge points can be visualized with the function F_VN_DrawContours.
F_VN_DrawContours(ipEdgePoints, -1, ipImageRes, aColorGreen, 5, hr);
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 |