Table Of Contents

Find Straight Edges (G Dataflow)

Last Modified: June 25, 2019

Finds straight edges, or lines, within a region of an image.

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optimized mode?

Boolean that specifies when an edge detection algorithm returns gradient values.

TRUE Edge detection algorithm that does not return gradient values.
FALSE Standard edge detection algorithm that returns gradient values.

Default: TRUE

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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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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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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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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 source image.

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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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search lines information

Information about the search lines that are used to detected the straight edges.

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start point

Start point of the search line in pixel units.

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end point

End point of the search line in pixel units.

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edges

Information of all the edges detected along the search line.

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location (pixel)

Location of the edge point in the image in pixel units.

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location (real-world)

Location of the edge point in the image in calibrated units.

When the image is not calibrated, this is the location in pixel units.

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distance (pixel)

Location of the edge from the first point of the search line along the boundary of the input ROI in pixels.

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distance (real-world)

Location of the edge from the first point of the search line along the boundary of the input ROI in calibrated units.

When the image is not calibrated, this distance is in pixel units.

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strength

Strength, or gradient magnitude, at the located edge.

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noise

Strength of the noise associated with the current edge.

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rising?

Boolean that specifies the polarity of the edge.

TRUE The edge is a rising edge.
FALSE The edge is not a rising edge.
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gradient values

Array that contains the calculated edge strengths along the search line.

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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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used edges

Edge points used to find each returned straight edge.

The outer array corresponds to the number of straight edges found. The inner array contains the edges points used to find each straight edge.

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edge information

Array that contains information about each detected edge.

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location (pixel)

Location of the edge point in the image in pixel units.

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location (real-world)

Location of the edge point in the image in calibrated units.

When the image is not calibrated, this is the location in pixel units.

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distance (pixel)

Location of the edge from the first point of the search line along the boundary of the input ROI in pixels.

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distance (real-world)

Location of the edge from the first point of the search line along the boundary of the input ROI in calibrated units.

When the image is not calibrated, this distance is in pixel units.

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strength

Strength, or gradient magnitude, at the located edge.

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noise

Strength of the noise associated with the current edge.

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rising?

Boolean that specifies the polarity of the edge.

TRUE The edge is a rising edge.
FALSE The edge is not a rising edge.
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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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