Direct modeling is a way of building 3D CAD geometry where you manipulate the model itself — its faces, edges, and bodies — rather than editing a recipe of parametric features. Tap a face and drag it outward, and the solid grows. Push it inward, and material is removed. The model is always the single source of truth.

How direct modeling works

In a direct modeler, every interaction operates on the current state of the geometry:

  • Push/pull: select a face and drag it along its normal to add or remove material.
  • Automatic booleans: when a pulled face intersects another body, the tool unions or subtracts automatically, so you rarely think about boolean operations explicitly.
  • Sketch-driven starts: most shapes still begin as a 2D sketch — a profile you extrude, revolve, or sweep into a solid — but once the solid exists, you edit the solid, not the sketch history.

Because there is no dependency chain, edits are fast and local. You never break a downstream feature by changing an upstream one, which is the classic frustration of history-based (parametric) CAD.

Where direct modeling shines

  • Concept and industrial design: exploring form quickly, where requirements change by the hour.
  • Touch and pencil interfaces: dragging a face with a fingertip is far more natural on a tablet than navigating a feature tree. This is why leading iPad CAD tools — including Shapr3D and OpenShape3D — are direct modelers first.
  • Editing imported geometry: a mesh or solid imported from another program has no feature history anyway; direct tools can still reshape it.
  • One-off parts and 3D printing: when you need a bracket, enclosure, or replacement part today, not a fully parameterized assembly.

Trade-offs to know

Direct modeling gives up the "change one dimension, rebuild everything" superpower of parametric CAD. If your work depends on families of parts driven by a dimension table, a history-based tool may fit better. Many modern products blend both: sketches with constraints and dimensions on the 2D side, direct manipulation on the 3D side.

Try it

OpenShape3D is a free, open-source direct-modeling CAD app for iPad and iPhone. It pairs sketch constraints and dimensions with Shapr3D-style push/pull editing, backed by the OpenCASCADE B-rep kernel — so the solids you make are exact, manufacturable geometry, not just meshes.