F_VN_MeasureMinEdgeDistance

Measure the minimum distance within the specified search window between 2 edges, 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_MeasureMinEdgeDistance : 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;
    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
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

Return value

HRESULT

Further information

The F_VN_MeasureMinEdgeDistance function localizes two linear edges and measures the minimum distance between them.

Parameter

Input image

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

Minimum distance ^{(Return value)}

The fMinDistance parameter returns the minimum distance between the two localized 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 using the aStartPoint, aEndPoint and nSearchLines parameters. 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.

Parameters for edge localization

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

Expert parameters

The F_VN_MeasureMinEdgeDistanceExp expert version contains additional parameters.

Application

The measurement of an edge distance looks like this, for example:

hr := F_VN_MeasureMinEdgeDistance(
    ipSrcImage         := ipImageIn,
    fMinDistance       := fMinDistance,
    aStartPoint        := aStartPoint,
    aEndPoint          := aEndPoint,
    eEdgeDirection     := TCVN_ED_LIGHT_TO_DARK,
    fMinStrength       := fMinStrength,
    nSearchLines       := nSearchLines,
    hrPrev             := hr);