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ScanExactlyNEdges3D


Module: Vision3DStandard

Locates a specified number of the strongest changes of surface height along a given path.

Name Type Range Description
inSurface Surface Input surface
inScanPath Path Path along which the scan is performed
inScanPathAlignment CoordinateSystem2D* Adjusts the scan path to the position of the inspected object
inSamplingStep Real* 0.0 - Distance between consecutive sampling points on the scan path; if Nil, the bigger of surface X and Y scales is chosen
inScanWidth Integer 1 - Width of the scan field in pixels
inSurfaceInterpolation InterpolationMethod Interpolation method used for extraction of surface points
inEdgeScanParams EdgeScanParams3D Parameters controlling the surface edge extraction process
inEdgeCount Integer 0 - Number of surface edges to be found
inEdgeSelection Selection Selection mode of the resulting edges
inMinDistance Real 0.0 - Minimal distance between consecutive edges
inMaxDistance Real* 0.0 - Maximal distance between consecutive edges
inLocalBlindness LocalBlindness* Defines conditions in which weaker edges can be detected in the vicinity of stronger edges
inMaxProfileGapWidth Integer* 0 - Maximal number of consecutive not existing profile points
outEdges SurfaceEdge1DArray? Found surface edges
outAlignedScanPath Path Path along which the scan is performed; in the image coordinate system
diagHeightProfile Profile Extracted surface height profile
diagResponseProfile Profile Profile of the edge (derivative) operator response
diagSamplingPoints PathArray Array of paths each one containing the sampling points that contributed to a single value of the extracted profile; in the image coordinate system
diagSamplingStep Real Used distance between consecutive sampling points on the scan path

Description

The operation scans the surface along inScanPath and finds a set of inEdgeCount surface edges perpendicular to the path. If no subset (of inEdgeCount elements) of detected edges meets the requirements of inEdgeScanParams.minMagnitude, inMinDistance, inEdgeScanParams.edgeTransition then the outputs are set to NIL.

The optional parameter inScanPathAlignment defines a transform to be performed on the inScanPath so that the actual scan path (outAlignedScanPath) is adjusted to the position of the object.

Note that in case of a scan path which is closed, the parameters controlling the distances between consecutive found objects do not control the distance between the first and the last of the found objects (counting from the beginning of the scan path).

The operation is very similar to ScanExactlyNEdges from 1D Edge Detection category, but there are some substantial differences. One of these is the possibility of absence of information, because some surface points may not exist at all. To detect such edges, where solely change of existence matters, Valid/Invalid options of inEdgeScanParams.EdgeTransition can be used. Outside the surface domain (i.e. rectangle defined by input surface width, height, offsets and scales) there are no valid or invalid points, so no edge can be found in the direct vicinity of the domain border.

Because in the Valid/Invalid mode all edges have equal strength, if inEdgeSelection is set to Best, it will be implicitly substituted with First selection option.

Please note that when the input surface has unequal scales along X and Y axes and the scan path is not parallel to any of the axes, the results may be slightly less accurate because of uneven sampling along axes.

Hints

  • Connect an input surface to the inSurface input.
  • Set inEdgeCount to the number of edges that are to be found (the N number).
  • Create inScanPath which is more or less perpendicular to the edges you want to detect. It should be long enough to anticipate all possible edge locations.
  • Define inEdgeScanParams.EdgeTransition to detect a particular edge type, and only that type.
  • Use a local coordinate system connected to inScanPathAlignment to automatically adjust the measurement to variable object position (optional).
  • If the noise level is high, try increasing inScanWidth and/or inEdgeScanParams.SmoothingStdDev.
  • If the expected number of edges cannot be found, try decreasing inEdgeScanParams.MinMagnitude. Verify this with the values on the diagResponseProfile output.
  • If consecutive edges are closer than 6 pixels apart, change inEdgeScanParams.ProfileInterpolation to Quadratic3.
  • Adjust inMinDistance (in surface coordinates) to filter out false edges that appear in proximity to other edges.

Remarks

Read more about Local Coordinate Systems in Machine Vision Guide: Local Coordinate Systems.

Complexity Level

This filter is available on Basic Complexity Level.

Filter Group

This filter is member of ScanEdges3D filter group.

See Also

  • ScanSingleEdge3D – Locates the strongest change of surface height along a given path.
  • ScanExactlyNEdges3D – Locates a specified number of the strongest changes of surface height along a given path.