Table Of Contents

Corner Detector (G Dataflow)

Last Modified: June 25, 2019

Detects corner points in an image using the Harris or Shi-Tomasi corner detection algorithms.

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image in

Reference to the source image.

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ROI descriptor

Region within which to search for corners.

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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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corner options

Options for corner detection.

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detector type

Corner detector algorithm to use.

Name Description
Harris corner Uses the Harris corner detector algorithm to detect corners. The Harris corner detector is a mathematical operator that finds corners in an image.
Shi-Tomasi corner Uses the Shi-Tomasi corner detector algorithm to detect corners. The Shi-Tomasi corner detector is based on the Harris corner detector, but there is a difference in the selection criteria of the corners. Shi-Tomasi works well in cases where the Harris corner detector fails.
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kernel size

Gaussian kernel size used to find the image features.

Supported sizes are 3, 5 and 7.

Default: 3

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min corner point strength

Minimum strength required to qualify as a corner.

The maximum strength is determined by the bit depth of the image. This value is applied to corners detected from pyramid level. At higher pyramid levels, or low resolution, corner strengths are higher compared to the higher resolution levels.

Default: 32

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pyramid level

Pyramid level that the node starts at to find corners.

Corners are found at the pyramid level and then propagated to the original image, which is level 0 of the pyramid. The default value is 1, which means the corners are found at the first level of the pyramid and then refined on the original image.

Default: 1

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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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corner point coordinates (pixel)

Locations of the corners detected in the image

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x

X-coordinate of the point.

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y

Y-coordinate of the point.

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corner point coordinates (real-world)

Rreal world locations of the corners detected in the calibrated image.

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x

X-coordinate of the point.

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y

Y-coordinate of the point.

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corner point strengths

Strength of the corners detected in the image.

The range is determined by the bit depth of the image.

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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.
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calibration valid flags

Boolean that indicates if the calibration information associated with the corners found is valid.

Invalid calibration information occurs when a pixel lies outside the area of the image that was calibrated.

True Calibration information is valid.
False Calibration information is invalid.

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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