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STL file at a glance

Origin

Stereolithography, 3D Systems, 1988

Extension

.stl

Encodings

ASCII and binary

Geometry

Triangle mesh with facet normals

Units

None stored in the file

3D InterOp
Read Write

Mesh import, binary or ASCII export

  • Building software that needs to read or write STL?

    3D InterOp is an SDK that lets your application import and export STL alongside 30+ CAD and BIM formats.
Aspect ASCII STL Binary STL

Encoding

Text

Binary

File size

Larger

Compact

Readability

Human-readable

Needs software

Use in practice

Inspection and debugging

Most common for exchange

  • Triangular facets

    Three vertices per facet

  • Normals

    An outward-pointing normal for each facet

  • Single object

    Usually one body, without scene structure

  • No units

    Units must be agreed between sender and receiver

  • Optional color

    Non-standard color extensions, not widely supported

  • No exact geometry

    No NURBS, analytic faces or feature history

Aspect STL OBJ 3MF

Color and materials

Limited, non-standard

Through a material file

Built in

Units

None

None

Defined in the file

Multiple objects

Generally one

Yes

Yes

Typical use

3D printing

Rendering and exchange

Additive manufacturing

  • Spatial doesn’t provide an STL viewer or converter for end users. 3D InterOp is for software developers who want their own application to read and write STL.
  • Treating STL as an engineering model

    STL captures a tessellated outer surface. It doesn’t preserve exact geometry, topology, features or product metadata like a native CAD model.

  • Poor mesh quality

    Misaligned edges, holes, floating parts, overlaps, double faces and open edges can break downstream workflows. See how to repair STL files.

  • Losing precision on export

    Moving from STEP or native CAD to STL discards exact geometry. A coarse tessellation can compromise the shape or delay manufacturing.

  • Wrong scale after import

    STL has no units. Sender and receiver have to agree on them, or the model arrives at the wrong size.

  • 3MF

    3D Manufacturing Format
    3MF
  • OBJ

    Wavefront mesh format
    OBJ
  • STEP (STP)

    ISO 10303 product data exchange
    STEP (STP)
  • Faceting

    Turning surfaces into triangles
    Faceting
  • glTF / GLB

    Modern web 3D format
    glTF / GLB
  • Industry · Additive manufacturing

    3D InterOp for additive manufacturing

    Bring exact CAD data from 30+ formats into your print-preparation software, and export the meshes your users need.
  • Add STL import and export to your software

    Evaluate 3D InterOp on your own models with support from Spatial’s engineers.

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