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Header: AVL.h
Namespace: avl
Module: Vision3DStandard

Locates multiple changes of surface height along a given path.


void avl::ScanMultipleEdges3D
	const avl::Surface& inSurface,
	const avl::ScanMap& inScanMap,
	const avl::EdgeScanParams3D& inEdgeScanParams,
	float inMinDistance,
	atl::Optional<float> inMaxDistance,
	atl::Optional<const avl::LocalBlindness&> inLocalBlindness,
	atl::Optional<int> inMaxProfileGapWidth,
	atl::Array<avl::SurfaceEdge1D>& outEdges,
	atl::Optional<avl::Profile&> outHeightProfile = atl::NIL,
	atl::Optional<avl::Profile&> outResponseProfile = atl::NIL


Name Type Range Default Description
Input value
inSurface const Surface& Input surface
Input value
inScanMap const ScanMap& Data precomputed with CreateSurfaceScanMap
Input value
inEdgeScanParams const EdgeScanParams3D& Parameters controlling the surface edge extraction process
Input value
inMinDistance float 0.0 - Minimal distance between consecutive edges
Input value
inMaxDistance Optional<float> 0.0 - NIL Maximal distance between consecutive edges
Input value
inLocalBlindness Optional<const LocalBlindness&> NIL Defines conditions in which weaker edges can be detected in the vicinity of stronger edges
Input value
inMaxProfileGapWidth Optional<int> 0 - NIL Maximal number of consecutive not existing profile points
Output value
outEdges Array<SurfaceEdge1D>& Found surface edges
Output value
outHeightProfile Optional<Profile&> NIL Extracted surface height profile
Output value
outResponseProfile Optional<Profile&> NIL Profile of the edge (derivative) operator response

Optional Outputs

The computation of following outputs can be switched off by passing value atl::NIL to these parameters: outHeightProfile, outResponseProfile.

Read more about Optional Outputs.


The operation scans the surface using inScanMap previously generated from a scan path and detects surface edges perpendicular to the path. Depending on the inEdgeScanParams.edgeTransition parameter, edges representing increase or decrease (or both) of surface height along the path will be taken into account.

When the number of edges to be found is known, one can use the ScanExactlyNEdges3D.

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 ScanMultipleEdges 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.

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.


  • Define inEdgeScanParams.EdgeTransition to detect a particular edge type, and only that type.
  • If too few edges are found, try decreasing inEdgeScanParams.MinMagnitude. Verify this with the values on the outResponseProfile 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.


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

See Also

  • CreateSurfaceScanMap – Precomputes a data object that is required for fast 1D edge detection in 3D.
  • 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.