Design Nomenclature / Digital Model Making
SDF
Also called signed distance field, signed distance function, implicit modeling, implicit surface
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.