Overview#
Looking at a shaded surface hides flaws. Analysis tools exaggerate them so you can see kinks, flat spots, and curvature jumps. Fusion's Inspect panel provides:
- Zebra Analysis: projects parallel stripes onto a body to show how reflections flow across faces. Smoother stripe transitions between surfaces indicate better continuity.
- Curvature Comb Analysis: plots curvature along an edge as a comb of teeth. It analyzes edges, not faces.
- Curvature Map Analysis: applies a color gradient to a body showing high and low curvature (Gaussian, Principal Minimum, Principal Maximum).
- Isocurve Analysis: applies UV mapping and curvature combs along isocurves to assess surface curvature quality.
- Also in Inspect: Draft Analysis and Accessibility Analysis, which check manufacturability rather than smoothness.
Where to find it#
- Inspect panel in the Design workspace (Inspect > Zebra Analysis, etc.). Use S and type the name if you cannot find it. Surface dialogs such as Patch, Extend and Ruled also have an Analysis tab for previews.
- For sketch curves: right-click the curve in the browser or canvas and choose Toggle Curvature Display.
Step by step#
Zebra Analysis#
- Choose Inspect > Zebra Analysis.
- Select the body (or bodies) to analyze.
- Adjust the settings: Direction (Vertical or Horizontal), Repeats (1 to 100 stripes), Opacity (0 to 100%), Lock Stripes, and High Quality.
- Orbit the model. Stripes should flow without sharp breaks across face boundaries you intended to be smooth.
- Read the stripes (see below). Click OK to keep the analysis in the browser, or cancel to discard it. Analyses saved in the browser can be toggled on and off.
Curvature Comb Analysis#
- Choose Inspect > Curvature Comb Analysis.
- Select the Edges to analyze, including edges on both sides of a seam to check the transition.
- Set Density (number of teeth per edge, 2 to 100) and Scale (length of the teeth).
- Look at how the comb behaves across adjacent edges (see below).
Curvature Map Analysis#
- Choose Inspect > Curvature Map Analysis.
- Pick the body and a Type: Gaussian, Principal Minimum or Principal Maximum.
- For Gaussian, adjust Display (Smooth or Bands) and Scale; Principal Minimum has a Maximum Limit and Principal Maximum a Minimum Limit (in design units). Adjust Opacity (0 to 100%) and optionally High Quality.
- Read the colors: for Gaussian, red/orange/yellow indicate positive curvature, green is flat, and blue/indigo/violet indicate negative curvature.
Isocurve Analysis#
- Choose Inspect > Isocurve Analysis.
- Select the bodies or faces, the Type (U and V, U, or V) and the number of Isocurves.
- Optionally check Curvature Combs and set their Density and Scale.
Reading the results#
Zebra stripes#
- Per Autodesk: stripe edges that do not align mean the boundary is not tangent (G0); aligned edges with a sharp angle mean tangent (G1); smooth throughout means curvature continuous (G2).
- Stripes that cross a seam without a break: at least tangent (G1).
- Stripes that meet at a seam but shift sideways or kink: positional match only (G0).
- Stripes that are tangent across the seam but change their spacing or bend abruptly: tangent but not curvature continuous.
- Stripes that flow with evenly changing spacing: curvature continuous (G2), the target for visible class-A surfaces.
- Wavy, nervous stripes inside a single face: poor surface definition (too many control points, wild parameterization).
Curvature comb#
- A comb with teeth that suddenly jump in length across a joint: curvature discontinuity (tangent but not G2).
- Teeth that point to different sides across a joint: curvature direction flips (an inflection or a bad match).
- Smooth, gradual teeth length changes: good curvature flow.
- Many small spikes along an edge: noisy geometry.
Curvature map#
- A sudden color step at an edge: curvature jump.
- A mostly uniform color on a nominally smooth area with isolated colored spots: dents or bumps.
Options reference#
| Tool | Option | What it does | Notes/default |
|---|---|---|---|
| Zebra | Body | Bodies to analyze | Multiple allowed |
| Zebra | Direction, Repeats, Opacity, Lock Stripes, High Quality | Stripe appearance | Repeats 1-100; Opacity 0-100% |
| Curvature Comb | Edges | Edges to plot | Edges of bodies only |
| Curvature Comb | Density | Teeth per edge | 2 to 100 |
| Curvature Comb | Scale | Tooth length gain | Adjust until visible |
| Curvature Map | Type | Gaussian, Principal Minimum, Principal Maximum | Gaussian shows total form |
| Curvature Map | Display, Scale | Smooth or Bands (Gaussian only), gradient scale | Bands makes steps obvious |
| Curvature Map | Maximum / Minimum Limit | Threshold for Principal Minimum / Maximum | In design units |
| Curvature Map | Opacity, High Quality | Visual tuning | High Quality may cost speed |
| Isocurve | Type, Isocurves | U and V, U or V; number per direction | |
| Isocurve | Curvature Combs, Density, Scale | Combs along each isocurve |
Tips and pitfalls#
Tip: Rotate the model while Zebra is on. Static views hide kinks that appear when the stripes shift.
Tip: Increase comb scale until the teeth are comfortably visible. Compare joint behavior, not absolute length.
Warning: Analysis results are display only (they live in the Browser's Analysis folder), and hidden bodies or unstitched seams can make a good model look bad. Stitch first, then analyze.
Warning: Curvature Comb works on edges only. To check a face interior, use Isocurve Analysis or Zebra.
Tip: Use Draft and Accessibility analysis near the end if the part is for molding or machining; they answer different questions.
Tip: Analyses persist in the browser's Analysis folder; toggle them off before exporting screenshots.
Worked example: diagnosing a dent in a bottle shoulder#
A bottle shoulder is lofted from a 60 mm diameter circle to a 28 mm neck over 40 mm of height. Under the viewport lighting it looks smooth, but you suspect a flat spot.
- Open Zebra Analysis on the shoulder surface at the default stripe density, direction vertical. The stripes bend smoothly around the shoulder but one stripe shows a kink at the seam where the tangent weights differ. A kink means G1 is broken or that curvature jumps there.
- Show the curvature of the profile spline (right-click it and choose Toggle Curvature Display; Curvature Comb Analysis itself works on body edges only), or run Curvature Comb on the edge of the lofted body. Raise the density until you can see the teeth, and adjust the scale so the longest tooth is about a quarter of the profile length. The comb shows a short tooth at the neck and a long one at the shoulder, with a sharp jump at 22 mm height: the curvature is discontinuous there.
- Use Curvature Map on the surface to confirm. The area around that height is a different color band from its neighbors, a visual 'step'.
- Go back to the profile spline, remove one interior fit point or add a tangent constraint, and re-run the comb. The teeth should form a gentle ramp. Update the loft and re-check zebra.
This cycle (find with zebra, locate with comb, confirm with map, fix the source curve, repeat) is the standard routine.
Which tool answers which question#
| Question | Tool | What to look for |
|---|---|---|
| Is the reflection smooth across a joint? | Zebra | Stripes continuous and without kinks |
| Where does the curve change its bend? | Curvature comb | Tooth length changes, sign flips |
| Where is the surface flat, saddle, or tight? | Curvature map | Color by Gaussian, Principal Minimum or Principal Maximum |
| How is the surface parameterized, and is it wavy? | Isocurve | Evenly spaced, smooth lines |
| Can the part be pulled from a mold? | Draft analysis | Color bands relative to the pull direction |
Reading numbers#
A comb tooth length is proportional to curvature: a 25 mm radius arc has curvature 0.04 per mm; at a scale that draws 1 unit per 0.01 curvature, its teeth are 4 units long. Doubling the radius to 50 mm halves the tooth length. A straight segment has zero length teeth. An inflection (S-curve) shows teeth swapping sides of the curve.
Failure modes and fixes#
| Symptom | Cause | Fix |
|---|---|---|
| Comb is invisible | Scale too small or density too low | Raise both; teeth should be easy to see. |
| Comb looks spiky and noisy | Density too high with a poorly parameterized spline | Lower density; if still noisy, rebuild the spline with fewer points. |
| Zebra stripes disappear | Wrong view or no surfaces selected | Select the faces; rotate the view so reflections cross the area. |
| Stripes look wavy on a good surface | Display quality is low | Check High Quality, then recheck. |
| Colors on the curvature map mislead | Scale or limit does not suit the surface | Adjust Scale (Gaussian) or the Maximum / Minimum Limit. |
| Analysis is not visible after editing | Its visibility was toggled off, or the selection no longer matches | Check the visibility icon in the Browser's Analysis folder, or right-click the analysis and Edit to reselect. |
A routine for sign-off#
- Run Zebra in two stripe directions, perpendicular to each other.
- Run Curvature Comb on at least two cross sections through each critical transition.
- Run Curvature Map and look for isolated hot spots.
- Save screenshots with the settings visible, so a reviewer can reproduce them.
Setting up analyses so results are comparable#
Analysis images are only useful if they can be repeated. Record: the stripe direction and repeats for zebra, the comb scale and density, the curvature map type and range, and the view orientation. Use the same settings each time you compare two revisions of a surface, otherwise a difference in apparent smoothness may only be a difference in settings. A good habit is to store these as a one-line note in the design, such as 'zebra: vertical, 20 repeats; comb: density 80, scale 100'.
Common misreadings#
- A comb that looks smooth at low density can hide a kink; raise the density before concluding.
- Zebra on a single face tells you nothing about continuity; select both faces of the seam.
- A curvature map can exaggerate tiny variations on an almost flat surface; adjust Scale or the limits.
- An isocurve display shows parameterization, not shape; two identical shapes can show different isocurves.
Practice exercise#
- Create two surface patches meeting at an edge, once with Connected continuity and once with Tangent.
- Run Zebra on both. Note how the stripes break in the Connected version.
- Run Curvature Comb on the shared edge and the edges either side. Observe the teeth.
- Repeat with Curvature continuity (if the dialog offers it). Expected: stripes flow with consistent spacing, and the comb teeth match in length across the seam.
Stretch challenge#
Make a spline with five fit points and view its comb. Move the middle point by 2 mm and watch the comb. Then use the same points with the spline's curvature handles (or fewer points) to get a monotonic comb. Expected result: the first spline shows an inflection (teeth switch sides) near the moved point, and the cleaned spline shows teeth that change length smoothly with no side switch. Extrude both to surfaces and confirm the zebra difference.
Related#
- Continuity G0 to G3
- Patch
- Surface Repair