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LocateSinglePointPattern


Module: FoundationPro

Finds an occurrence of the pattern in the input points.

Applications

Can be used to find an entire object after finding its characteristic points with tools such as Template Matching or DL_LocatePoints.
Name Type Range Description
Input value inPoints Point2DArray Input points
Input value inPointLabels IntegerArray* Categories that the input points belong to
Input value inPattern Point2DArray Point pattern to be found
Input value inPatternLabels IntegerArray* Categories that the pattern points belong to
Input value inReferenceFrame Rectangle2D* Exact position of the model object associated with the pattern in the image
Input value inAllowRotation Bool Flag indicating whether rotation is allowed as a part of output alignment
Input value inMinAngle Real Start of range of possible rotations
Input value inMaxAngle Real End of range of possible rotations
Input value inAllowScale Bool Flag indicating whether scale is allowed as a part of output alignment
Input value inMinScale Real 0.0 - Start of range of possible scales
Input value inMaxScale Real 0.0 - End of range of possible scales
Input value inTilingFactor Real 0.000001 - 1.0 Defines relative size of the square tile on the plane during initial detection
Input value inMinInitialScore Real 0.0 - 1.0 The minimum proportion of points correctly matched during initial detection
Input value inMaxDeviation Real 0.0 - Maximal distance between two points considered matched
Input value inMinScore Real 0.0 - 1.0 The minimum proportion of points correctly matched
Output value outObject Rectangle2D? Bounding rectangle of the found pattern occurrence
Output value outAlignedPattern Point2DArray? The aligned input pattern points
Output value outAlignment CoordinateSystem2D? The transform that align the input pattern to the input points
Output value outPatternSkeleton Segment2DArray? The skeleton of the aligned input pattern points

Description

The filter finds location of a pattern of points in the set of input points. The possible rotation and scale of the found occurrence can be fully controlled using proper values of inAllowRotation, inMinAngle, inMaxAngle, inAllowScale, inMinScale and inMaxScale parameters.

The location routine consists of two phases. Only the inTilingFactor and inMinInitialScore parameters have an effect on the initial phase. Internally, the whole plane is then divided into square tiles which size depends on inTilingFactor and the average distance between two points from inPoints. A transformation becomes a candidate to be a valid pattern occurrence if at least inMinInitialScore fraction of pattern points reside in the right tiles. The candidate transformation proceeds to the second phase, where it is refined to be possibly best fitted to the data points. The result transformation is considered to be a valid output alignment if at least inMinScore fraction of aligned pattern points are at most inMaxDeviation away from their closest data points.

The most difficult part to achieve reliable results seems to be the proper setting of the inTilingFactor parameter. Because of its existence, the algorithm will work especially well when the pattern consists of not too many points and distances between them are more or less equal i.e. the ratio of the greatest distance between pattern points and the smallest distance between pattern points is small. If this is not the case and the default value for inTilingFactor does not work well, one should try to adjust the value keeping in mind that the greater values should be used when the pattern visible in the inPoints is distorted and the smaller values will work best when only small distortion is present. In case of further problems with choosing the right inTilingFactor value, one can also try lowering inMinInitialScore value.

The filter performance depends heavily on the number of the pattern points. Because of that fact, it is highly advisable for the pattern to be as small as possible. The performance can be poor even for patterns with more than 15 points. Note that the shape of the pattern also matters. The execution time for symmetrical patterns is generally bigger than for asymmetrical ones.

Examples

Description of usage of this filter can be found in examples and tutorial: Photometric Stereo Braille.

inPattern input with selected point pattern to be found

LocateSinglePointPattern performed on points acquired by DL_LocatePoints

Errors

This filter can throw an exception to report error. Read how to deal with errors in Error Handling.

List of possible exceptions:

Error type Description
DomainError Input pattern and input pattern labels sizes are not equal in LocateSinglePointPattern.
DomainError Input pattern is empty in LocateSinglePointPattern.
DomainError Input points and input point labels sizes are not equal in LocateSinglePointPattern.
DomainError Point labels should be both present or both absent in LocateSinglePointPattern.

Complexity Level

This filter is available on Advanced Complexity Level.

Filter Group

This filter is member of LocatePointPatterns filter group.

See Also