Table Of Contents

Find Edge (G Dataflow)

Last Modified: June 25, 2019

Identifies straight edge lines within a region of an image.

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options

Cluster defining the parameters of the edge detection algorithm and the information that is overlaid on the result image.

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search direction

Direction in which the Region of Interest (ROI) is examined when straight edge detection is performed.

Name Value Description
left to right 0

(Default) Searches for edges from left to right

right to left 1

Searches for edges from right to left

top to bottom 2

Searches for edges from top to bottom

bottom to top 3

Searches for edges from bottom to top

Default: left to right

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edge options

Inputs used to compute the edge gradient information and detect the edges.

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edge polarity

Polarity of the edges to be found.

Name Value Description
all edges 0

(Default) Searches for all edges

rising edges 1

Searches for rising edges

falling edges 2

Searches for falling edges

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kernel size

Size of the edge detection kernel.

Default: 3

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width

Number of pixels averaged perpendicular to the search direction to compute the edge profile strength at each point along the search ROI.

Default: 3

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minimum edge strength

Minimum edge strength, or gradient magnitude, required for a detected edge.

Default: 10

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interpolation type

Interpolation method used to locate the edge position.

Name Description
zero order Rounds to the nearest integral edge location
bilinear Uses bilinear interpolation to compute the edge location
bilinear fixed (Default) Uses the fixed-point computation of bilinear interpolation to determine the edge location
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data processing method

Method used to process the data extracted for edge detection.

Name Description
average (Default) Averages the data extracted for edge detection
median Takes the median of the data extracted for edge detection
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show search area

Boolean that specifies if the ROI is overlaid on the image.

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show search lines

Boolean that specifies if the search lines used to locate the edges are overlaid on the image.

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show edges found

Boolean that specifies if the locations of the edges found are overlaid on the resulting image.

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show result

Boolean that specifies if the edge found is overlaid on the resulting image.

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search area color

Color used to overlay the search area.

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search lines color

Color used to overlay the search lines.

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edge locations color

Color used to overlay the edge locations.

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result color

Color used to overlay the result.

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overlay group name

Group name for the step overlays.

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image in

Reference to the source image.

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ROI descriptor

Rectangle, rotated rectangle, or other four-side rectangular polygon within which the edge detection is performed.

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global rectangle

Coordinates of the bounding rectangle.

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contours

Individual shapes that define an ROI.

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ID

Object specifying if contour is the external or internal edge of an ROI.

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Type

Shape type of the contour.

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Coordinates

Relative position of the contour.

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line fit options

Options used to detect the straight edges.

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number of lines

Number of straight edges to find.

Default: 1

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type

Method used to find the straight edge.

Name Description
first edge rake (Default) Fits a straight edge on the first points detected using a rake
best edge rake Fits a straight edge on the best points detected using a rake
Hough edge rake Finds the strongest straight edge using all points detected on a rake
first edge projection Uses the location of the first projected edge as the straight edge
best edge projection Finds the strongest projected edge location to determine the straight edge
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min. score

Minimum score of a detected straight edge.

Default: 10

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max. score

Maximum score of a detected straight edge.

Default: 1000

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orientation

Angle at which the straight edge is expected to be found.

Default: 0

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angle range

Positive and negative range around the orientation within which the straight edge is to be found.

Default: 45

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angle tolerance

Expected angular accuracy of the straight edge.

Default: 1

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step size

Gap in pixels between the search lines used with the rake-based methods.

Default: 7

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min. SNR (db)

Minimum signal to noise ratio (SNR) of the edge points used to fit the straight edge.

Default: 0

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min. points (%)

Minimum number for points as a percentage of the number of search lines to include in the detected straight edge.

Default: 25%

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Hough iterations

Number of iterations used in the Hough-based method.

Default: 5

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coordinate system

Input that specifies the coordinate system to use.

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reference system

Cluster containing origin, angle (deg), and axis reference.

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origin

Point cluster that specifies the origin of the base-reference coordinate system.

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x

X-coordinate of the center of the circle.

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y

Y-coordinate of the center of the circle.

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angle (deg)

Angle that the base-reference coordinate system makes with the image coordinate system.

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axis reference

Element defined as direct or indirect.

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measurement system

Cluster containing origin, angle (deg), and axis reference.

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origin

Point cluster that specifies the origin of the base-reference coordinate system.

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x

X-coordinate of the center of the circle.

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y

Y-coordinate of the center of the circle.

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angle (deg)

Angle that the base-reference coordinate system makes with the image coordinate system.

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axis reference

Element defined as direct or indirect.

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error in

Error conditions that occur before this node runs.

The node responds to this input according to standard error behavior.

Standard Error Behavior

Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

error in does not contain an error error in contains an error
If no error occurred before the node runs, the node begins execution normally.

If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.

If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.

Default: No error

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image out

Reference to the image input.

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straight edges

Information about the detected straight edges.

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point1 (pixels)

Start point of the detected straight edge in pixel units.

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point2 (pixels)

End point of the detected straight edge in pixel units.

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point1 (real-world)

Start point of the detected straight edge in calibrated units.

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point2 (real-world)

End point of the detected straight edge in calibrated units.

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angle (pixel)

Angle the detected straight edge makes with the axis perpendicular to the search direction.

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angle (real-world)

Angle the detected straight edge makes with the axis perpendicular to the search direction in calibrated units.

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score

Score of the detected straight edge.

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straightness

Value of the detected straight edge.

Straightness is defined as the root mean squared error of the fitted line that represents the detected straight edge. A value of 0 indicates a perfectly straight line.

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average SNR (dB)

Average signal-to-noise (SNR) ratio along the detected straight edge.

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calibration valid

Boolean that indicates if the calibration information associated with the edges found along the search line is valid.

TRUE Calibration information is valid.
FALSE Calibration information is invalid for any pixel that is used for edge detection.
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coordinate system dup

Reference to the coordinate system.

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error out

Error information.

The node produces this output according to standard error behavior.

Standard Error Behavior

Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

error in does not contain an error error in contains an error
If no error occurred before the node runs, the node begins execution normally.

If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.

If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.

Where This Node Can Run:

Desktop OS: Windows

FPGA: Not supported

Web Server: Not supported in VIs that run in a web application


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