A mesh-based 3D model represents an object's surface as connected polygons, usually triangles. It is a practical choice when a digital twin needs an interactive view of a large asset in a browser: the geometry renders efficiently without requiring specialized viewing software. A mesh approximates shape rather than preserving every detail. section 7.1 section 2.4.2
The model is built from a small set of geometric parts:
- Vertices locate points with x, y, and z coordinates; edges connect them. section 7.1
- Faces close those edges into polygons, such as triangles or quadrilaterals. Normals specify directions used for lighting and rendering. section 7.1
A cube written as an OBJ file
A cube can be defined in a text editor with eight vertex records, six face-normal records, and six face records. In the OBJ example, each face lists its vertices and a normal. Reading that file makes the relationship between coordinates, surfaces, and rendered appearance concrete; everyday workflows can instead export geometry from modeling software. section 7.1
Listing 7.1 Definition of a 3D cube in OBJ file format
# Vertices v -1.0 -1.0 1.0 v 1.0 -1.0 1.0 v 1.0 1.0 1.0 v -1.0 1.0 1.0 v -1.0 -1.0 -1.0 v 1.0 -1.0 -1.0 v 1.0 1.0 -1.0 v -1.0 1.0 -1.0 # Face normals vn 0.0 0.0 1.0 # Front face normal vn 1.0 0.0 0.0 # Right face normal vn 0.0 0.0 -1.0 # Back face normal vn -1.0 0.0 0.0 # Left face normal vn 0.0 1.0 0.0 # Top face normal vn 0.0 -1.0 0.0 # Bottom face normal # Faces (format: vertex//normal) f 1//1 2//1 3//1 4//1 # Front face f 2//2 6//2 7//2 3//2 # Right face f 6//3 5//3 8//3 7//3 # Back face f 5//4 1//4 4//4 8//4 # Left face f 4//5 3//5 7//5 8//5 # Top face f 5//6 6//6 2//6 1//6 # Bottom face
Inspect the `v`, `vn`, and `f` records to see how a compact set of points defines the cube's faces and their normals. section 7.1
Choose mesh density for the task. More geometry improves the shape approximation but costs computation; less geometry helps responsiveness. Meshes suit equipment views and interactive walkthroughs, not every spatial decision. BIM carries building-element meaning, parametric models support precise design changes, and LiDAR point clouds serve uses such as as-built inspection where high accuracy matters. Simulation also uses meshes, but its elements divide a domain for physics calculations rather than merely describing a surface for display. section 2.4.2 section 2.7 section 7.6 section 9.5
