Deviation Analysis

The Deviation Analysis tool compares two objects to quantify geometric differences, displaying point-to-point distance deviations as color-mapped visualizations with statistical summaries. This analysis is essential for quality control, manufacturing validation, reverse engineering verification, and any workflow requiring quantitative comparison between actual and reference geometries.

Understanding Deviation Measurement

Deviation analysis – also known as nominal-actual comparison – calculates the distance from each point on an actual object to the closest point on a reference object. The results reveal how much the actual geometry differs from the reference, with positive and negative values (in signed mode) indicating whether points are outside or inside the reference boundary.

The analysis produces a continuous scalar field mapped to the actual object's surface, enabling immediate visual identification of regions that deviate from the reference geometry. Statistical summaries provide overall conformance metrics.

Manufacturing and Quality Control Disclaimer

Deviation analysis results are provided for quality assessment and research purposes. Results should be validated by qualified engineers or metrologists before making manufacturing acceptance decisions. Measurement accuracy depends on mesh quality, object alignment, and algorithm parameters.

Comparison Modes

The tool supports three comparison configurations:

Mode	Actual Object	Reference Object	Use Case
Mask vs. Mask	Mask (3D preview)	Mask (3D preview)	Compare two segmented structures
Mask vs. Surface	Mask (3D preview)	Surface mesh	Compare segmentation against CAD or imported geometry
Surface vs. Surface	Surface mesh	Surface mesh	Compare two surface models directly

Accessing the Tool

1. Navigate to the Analyze ribbon tab.
2. Click the Deviation Analysis button.
3. Select the comparison mode from the dropdown menu:
   • Mask vs. Mask – Compare two mask objects using their 3D preview surfaces.
   • Mask vs. Surface – Compare a mask object against a surface mesh.
   • Surface vs. Surface – Compare two surface mesh objects.

Analysis Configuration

Creating a New Analysis

1. In the Analysis Selection section, click Select analysis to open the Deviation Analysis Editor dialog.
2. Click New Analysis to create a new analysis configuration.
3. Configure the analysis parameters (detailed below).
4. Click Load to load the selected analysis and close the dialog.

Analysis Parameters

The Deviation Analysis Editor provides the following configuration options:

Parameter	Description
Analysis Name	User-defined name for the analysis. Double-click to rename.
Actual Object	The object being evaluated (mask or surface depending on mode).
Reference Object	The reference geometry to compare against.
Surface Quality	(Mask-based modes only) Quality of the 3D preview surface: Optimal, High, Medium, or Low.
Method	Deviation calculation method: Signed or Unsigned.
Above Max. Range Color	Color displayed for deviation values above the visualization range.
LUT	Lookup table (color map) for visualizing deviation values.
Below Min. Range Color	Color displayed for deviation values below the visualization range.
Range (mm)	Current visualization range (read-only, updated after analysis).

Calculation Methods

Signed Distance

The Signed method calculates directional deviation:

• Positive values: Points on the actual object that are outside (beyond) the reference surface.
• Negative values: Points on the actual object that are inside the reference surface.
• Zero: Points that coincide with the reference surface.

This method is ideal for:

• Identifying whether manufacturing added or removed material
• Detecting shrinkage vs. expansion
• Understanding directional differences

Unsigned Distance

The Unsigned method calculates absolute deviation:

• All values are positive: Represents the absolute distance from actual to reference.
• Zero: Points that coincide with the reference surface.

This method is useful when:

• Only the magnitude of deviation matters
• Comparing objects where inside/outside distinction is not meaningful
• Creating tolerance bands around a nominal geometry

tip

Use Signed distance when you need to understand whether deviations are inward or outward. Use Unsigned when you only care about the magnitude of deviation regardless of direction.

Running the Analysis

1. After loading an analysis configuration, click Run Analysis.
2. A progress dialog appears while the analysis computes.
3. Upon completion:
   • The actual object displays color-mapped deviation values in 3D and 2D views.
   • The histogram updates with the deviation distribution.
   • The statistics table populates with summary metrics.

note

Ensure both actual and reference objects are properly aligned before running the analysis. Use the Global Registration tool if alignment is needed.

Interpreting Results

Visualization

The actual object displays a color gradient representing deviation values:

For Signed distance:

• Blue/cool colors: Negative deviation (actual is inside reference)
• Green/neutral colors: Near-zero deviation (good conformance)
• Red/warm colors: Positive deviation (actual is outside reference)

For Unsigned distance:

• Blue/cool colors: Low deviation (good conformance)
• Red/warm colors: High deviation (poor conformance)

Use the histogram range sliders to focus on specific deviation intervals.

Statistics

The statistics table displays key metrics:

Statistic	Description
Actual Object	Name of the evaluated object.
Reference Object	Name of the reference object.
Method	Signed or Unsigned calculation method.
Max. Deviation (mm)	Largest positive deviation value.
Max. Deviation Points	Coordinates of the maximum deviation location.
Min. Deviation (mm)	Smallest deviation value (most negative for signed).
Min. Deviation Points	Coordinates of the minimum deviation location.
Mean Deviation (mm)	Average deviation across all points.
Standard Deviation	Variation in deviation values.
Range (mm)	Current visualization range.
Mean Deviation within Range	Average for points within the selected range.
Area Below Min. Range (%)	Percentage of surface below the minimum range.
Area Above Max. Range (%)	Percentage of surface above the maximum range.
Area Within Range (%)	Percentage of surface within the selected range.

Cumulative Statistics

When using the Cumulative relative surface histogram type, additional statistics appear:

Statistic	Description
Cumulated 90% (mm)	Deviation value at which 90% of surface area is accounted for.
Cumulated 95% (mm)	Deviation value at which 95% of surface area is accounted for.
Cumulated 98% (mm)	Deviation value at which 98% of surface area is accounted for.

These percentile values are useful for tolerance specification and pass/fail criteria.

Interactive Features

Feature	Description
Show Maximum	Displays an annotation at the point of maximum deviation.
Show Minimum	Displays an annotation at the point of minimum deviation.
Pick Point	Enable interactive picking to display deviation at any clicked location.

Typical Workflows

Manufacturing Quality Control

1. Import the CAD reference model as a surface.
2. Segment the scanned manufactured part to create a mask.
3. Align the actual part to the reference using Global Registration.
4. Create a Mask vs. Surface deviation analysis.
5. Run the analysis with Signed method.
6. Adjust the range to tolerance limits (e.g., ±0.5 mm).
7. Review the percentage of surface within tolerance.
8. Export a PDF report for quality documentation.

Before/After Comparison

1. Segment structures from two different time points.
2. Align the datasets using image registration.
3. Create a Mask vs. Mask deviation analysis.
4. Run with Signed method to see growth vs. shrinkage.
5. Use Show Maximum/Minimum to locate areas of greatest change.

Reverse Engineering Validation

1. Import the original reference geometry.
2. Generate a surface from the reverse-engineered model.
3. Align surfaces using Global Registration.
4. Create a Surface vs. Surface deviation analysis.
5. Run with Unsigned method to assess reconstruction accuracy.
6. Review cumulative statistics for overall quality metrics.

Tolerance Band Visualization

1. Configure deviation analysis between actual and nominal geometry.
2. Set the visualization range to the tolerance limits (e.g., -0.2 to +0.2 mm).
3. Points displayed in the range colors are within tolerance.
4. Below/above range colors immediately highlight out-of-tolerance regions.
5. The "Area Within Range" statistic gives the conformance percentage.

Exporting Results

CSV Export

Click Export and select CSV to save:

• Statistical summary data
• Deviation distribution histogram data
• Per-point deviation values (optional)

PDF Report

Click Export and select PDF Report to generate a formatted document containing:

• Analysis configuration and comparison parameters
• 3D visualization screenshots
• Histogram and statistics
• Deviation location annotations

See PDF Report for detailed report customization options.

Best Practices

1. Align objects before analysis: Misalignment causes systematic deviation that obscures true geometric differences. Use Global Registration for automatic alignment.

2. Match surface quality to requirements: For mask-based analyses, use Optimal quality for final reports and Medium for quick exploration.

3. Choose the appropriate method: Use Signed for directional analysis; Unsigned when only magnitude matters.

4. Set meaningful tolerance ranges: Configure the visualization range to match your acceptance criteria for immediate pass/fail visualization.

5. Consider mesh resolution: Both actual and reference meshes should have sufficient resolution to capture the geometric detail you want to measure.

6. Document comparison parameters: Include alignment method and analysis settings in reports for reproducibility.

Troubleshooting

Issue	Possible Cause	Solution
Large systematic deviations	Objects not aligned	Run Global Registration before analysis
One-sided deviation values	Signed method with objects swapped	Swap actual and reference objects, or use Unsigned
Noisy deviation map	Coarse mesh resolution	Increase surface quality for masks; refine surface meshes
Missing data in some regions	Non-overlapping geometry	Ensure objects cover the same spatial region

Related Resources

• Analyze Tab Overview – Overview of all analysis tools
• Wall Thickness Analysis – Measure material thickness
• Global Registration – Align objects before comparison
• PDF Report – Generate analysis reports
• Analysis Operations API – Scripting support for analysis automation