BestFit Component

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Align a scanned point cloud with a CAD model

BestFit calculates a transformation that aligns measured points with reference CAD geometry. It is intended for scan-to-CAD registration in dimensional inspection, metrology and comparison of manufactured parts with their nominal design.

The algorithm evaluates point deviations from reference surfaces or wireframes, constructs an error function and optimizes translation and rotation. The result is a transformation that the application can apply to the scanned data.

From point deviations to a transformation matrix

The calculation has three connected stages:

1. Project and measure. Calculate each input point’s deviation from the nominal shape, using reference surfaces or wireframes.
2. Construct the error function. Combine the point deviations and their dependence on the transformation parameters into an overall alignment objective.
3. Optimize the placement. Solve for translation and rotation that minimize the global deviation represented by that objective.

The output is a transformation matrix combining rotation and translation. Applying it places the measured point cloud in the reference model’s coordinate system for subsequent comparison. The C++ API allows this operation to be integrated into an inspection application rather than requiring a separate manual alignment tool.

Reference geometry selection is part of that integration: a surface-based comparison and a wireframe-based comparison express different alignment requirements. Choose the relevant nominal geometry before interpreting the remaining point deviations as manufacturing differences.

Integrate registration into an inspection workflow

1. Load the nominal CAD model and measured points in consistent units.
2. Select the geometry and points relevant to the alignment task.
3. Calculate the alignment transformation and apply it to the measured data.
4. Inspect residual deviations against the application’s acceptance criteria.

Alignment is one operation in a measurement workflow. It does not by itself establish scanning accuracy or certify that a part meets a tolerance. Evaluate initialization, partial coverage, outliers and symmetric geometry with data representative of your process.

What to evaluate

Specify point count, CAD complexity, expected displacement, required processing time and the desired deviation reporting. Compare results using a known reference alignment and identify how the application should handle an unsuitable fit.

Use CAD exchange components to bring reference geometry into OCCT. If the task is to construct a surface from measured points rather than align them, see Surface from Scattered Points.

Request a BestFit evaluation or discuss metrology application development.