Design Nomenclature / Digital Model Making
SDF
Also called signed distance field, signed distance function, implicit modeling, implicit surface
This entry has not been translated yet and is shown in English.
Form defined as a function returning the distance from any point to the nearest surface — negative inside, positive outside. The surface is the zero level set and is never stored. Booleans become min and max, offsets become addition, blends become a smooth minimum, and the result is watertight by construction.
In practice
“Implicit modeling” is the older, broader name; SDF is the representation nearly everyone now means. Ask whether the field is evaluated live or sampled to a grid — the second is voxels wearing a better word.
Not to be confused with
- Voxel ModelingWorking on a regular 3D grid of samples, each cell occupied or carrying a value. Topology changes are trivial — you are editing an array, so self-intersection is not expressible — but resolution is fixed and isotropic, memory scales cubically, and every surface must be extracted by an isosurface pass that leaves a grid signature.
- CSGA scheme in which form is a tree of primitives combined by set operations, and the tree — not the resulting surface — is the model. Evaluate it and you get geometry; keep it and you can still change the radius of a hole from twenty steps back.
- BooleanA set operation — union, difference, intersection — between two volumes. It is only well defined on closed, manifold, non-self-intersecting input; give it an open mesh and the result is whatever the implementation guesses. Mesh booleans also leave n-gons and coincident geometry along the cut, which is legal and still needs cleanup.