STEP vs IGES: what one cylinder demonstrates

STEP and IGES can carry CAD geometry that a mesh format cannot express as exact surfaces. What survives a transfer depends on the source entities, the writer, and the receiving importer. A file extension alone cannot establish that every part or trimmed surface arrived intact.

The same source geometry

We created a cylinder with a 10 mm radius and 20 mm height, then exported it as STEP and IGES. The source files contain curved geometry. Reading each with the same kernel settings, 0.1 mm linear deflection and 0.5 radians angular deflection, produces 124 triangles and a 20 × 20 × 20 mm mesh bounding box.

The match is useful evidence for these files. Both pass through the same browser kernel, so it is not an independent comparison of two unrelated CAD systems. It also says nothing about a complex assembly, unsupported entities, or another exporter's tolerance decisions.

The viewer displays a mesh

The browser evaluates the CAD surfaces and turns them into triangles for display and mesh export. Increasing triangle density does not restore a source application's modeling history. After an STL export, a cylinder is represented by planar facets, even when those facets look smooth at the current zoom.

Open CASCADE's overview describes its STEP and IGES translation facilities. Our browser uses the occt-import-js interface, whose documented settings distinguish absolute deflection from a bounding-box ratio.

Use a known dimension as a check

Confirm scale and inspect missing faces or parts before a handoff. When the receiving CAD system supports both formats, compare exports from your actual source model. Keep the original native CAD file if you need constraints, features, or edit history. The cylinder downloads provide a reproducible starting point, with known geometry and the exact settings recorded in the case study.