Tessellation Quality Explained: Linear and Angular Deflection

Every time exact CAD geometry becomes a mesh — for printing, rendering or the web — a tessellator decides how many triangles to spend and where. Two parameters control it, and understanding them ends the guesswork about quality presets.

Linear deflection: distance error

Linear deflection is the maximum distance allowed between the true surface and the triangle approximating it, in model units. A 0.1 mm deflection on a large housing is invisible; the same setting on a 3 mm watch component is disastrous. That is why the value is best expressed relative to model size — our presets scale it from the model’s bounding box automatically.

Angular deflection: curvature error

Angular deflection caps the angle between adjacent facets. It is what keeps small cylinders round: a hole 2 mm across can pass a loose linear tolerance with a handful of flat facets, but a 0.3 rad angular limit forces enough segments to look — and print — round.

What the presets mean

• Draft — fastest, visibly faceted. Fit checks and quick previews.
• Normal — balanced. Correct for most FDM 3D printing.
• Fine — smooth curves, several times more triangles. Resin printing and close-up rendering.
• Precision — near-exact surfaces, largest files. Simulation and inspection.

Triangles are a budget

More triangles are not free: a slicer, a browser scene or a game engine pays for every one, and beyond “smooth enough” extra density adds cost with zero visible gain. Convert once at Fine, inspect the silhouette in the 3D viewer, then step down until just before facets appear — that is your budget. Try it on a real part with the STEP to STL converter.