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# ScanMultipleEdges3D_Direct

Locates multiple changes of surface height along a given path.

### Syntax

C++
C#

void avl::ScanMultipleEdges3D_Direct
(
const avl::Surface& inSurface,
const avl::Path& inScanPath,
atl::Optional<const avl::CoordinateSystem2D&> inScanPathAlignment,
atl::Optional<float> inSamplingStep,
int inScanWidth,
avl::InterpolationMethod::Type inSurfaceInterpolation,
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::Path&> outAlignedScanPath = atl::NIL,
atl::Optional<avl::Profile&> outHeightProfile = atl::NIL,
atl::Optional<avl::Profile&> outResponseProfile = atl::NIL,
atl::Array<avl::Path>& diagSamplingPoints,
float& diagSamplingStep
)


### Parameters

Name Type Range Default Description
inSurface const Surface& Input surface
inScanPath const Path& Path along which the scan is performed
inScanPathAlignment Optional<const CoordinateSystem2D&> NIL Adjusts the scan path to the position of the inspected object
inSamplingStep Optional<float> 0.0 - NIL Distance between consecutive sampling points on the scan path; if Nil, the bigger of surface X and Y scales is chosen
inScanWidth int 1 - 5 Width of the scan field in pixels
inSurfaceInterpolation InterpolationMethod::Type Bilinear Interpolation method used for extraction of surface points
inEdgeScanParams const EdgeScanParams3D& EdgeScanParams3D ( ProfileInterpolation: Quadratic4 SmoothingStdDev: 0.6f MinMagnitude: 5.0f EdgeTransition: LowToHigh ) Parameters controlling the surface edge extraction process
inMinDistance float 0.0 - 0.0f Minimal distance between consecutive edges
inMaxDistance Optional<float> 0.0 - NIL Maximal distance between consecutive edges
inLocalBlindness Optional<const LocalBlindness&> NIL Defines conditions in which weaker edges can be detected in the vicinity of stronger edges
inMaxProfileGapWidth Optional<int> 0 - 1 Maximal number of consecutive not existing profile points
outEdges Array<SurfaceEdge1D>& Found surface edges
outAlignedScanPath Optional<Path&> NIL Path along which the scan is performed; in the image coordinate system
outHeightProfile Optional<Profile&> NIL Extracted surface height profile
outResponseProfile Optional<Profile&> NIL Profile of the edge (derivative) operator response
diagSamplingPoints Array<Path>& 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 float& Used distance between consecutive sampling points on the scan path

### Optional Outputs

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

### Description

The operation scans the surface along inScanPath 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_Direct.

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 ScanMultipleEdges_Direct 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.

### Hints

• 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.

### Remarks

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