Project 11: STEP File Data Explorer (Interoperability)

Build a STEP parser that extracts geometry and topology data into a readable form.

Project Overview

Attribute Value
Difficulty Level 2: Intermediate
Time Estimate Weekend
Main Language C++
Alternative Languages Python, Rust, C
Knowledge Area CAD interoperability
Tools STEP files from CAD tools
Main Book “Geometric Modeling” by Michael E. Mortenson

What you’ll build: A parser that reads STEP files and outputs a structured summary of geometry, topology, and attributes.

Why it teaches computational geometry: Real CAD work requires interoperability. Parsing STEP reveals how models are encoded and exchanged.

Core challenges you’ll face:

  • Parsing STEP entity syntax reliably
  • Mapping STEP entities to internal structures
  • Handling large and nested relationships

Real World Outcome

You will load a STEP file and output a readable report listing faces, edges, curves, and their relationships.

Example Output:

$ ./step_explorer --input part.step
Entities: 1240
Advanced_Brep_Shape_Representation: 1
Faces: 56
Edges: 84
Surfaces: 12

Verification steps:

  • Compare extracted counts with CAD tool summaries
  • Inspect a few entities to confirm relationships

The Core Question You’re Answering

“How do CAD systems serialize and exchange complex geometry reliably?”

Understanding STEP gives you the ability to import/export models in real pipelines.

Concepts You Must Understand First

Stop and research these before coding:

  1. STEP entity graph
    • How are entities referenced and linked?
    • Book Reference: “Geometric Modeling” by Michael E. Mortenson, Ch. 14
  2. B-Rep in STEP
    • How are faces, edges, and vertices represented?
    • Book Reference: “Geometric Modeling” by Michael E. Mortenson, Ch. 10
  3. Parsing structured formats
    • How do you parse nested and referenced entities safely?
    • Book Reference: “Compilers: Principles, Techniques, and Tools” by Aho et al., Ch. 4

Questions to Guide Your Design

  1. Parser scope
    • Which STEP entity types will you support first?
    • How will you handle unknown or vendor-specific entities?
  2. Output format
    • Will you export to JSON for inspection?
    • How will you represent relationships between entities?

Thinking Exercise

Entity Reference Chain

Given a face entity that references a surface, outline the chain of references needed to reconstruct that surface.

Questions while working:

  • How do you prevent circular reference loops?
  • Why is STEP an entity graph rather than a tree?

The Interview Questions They’ll Ask

Prepare to answer these:

  1. “What is a STEP file and why is it important?”
  2. “How does STEP represent B-Rep geometry?”
  3. “Why is parsing STEP challenging?”
  4. “How do you manage entity references?”
  5. “What are common interoperability pitfalls in CAD?”

Hints in Layers

Hint 1: Starting Point Start by parsing the header and entity lines into a simple index.

Hint 2: Next Level Resolve references only for a small subset of entity types.

Hint 3: Technical Details Build a graph structure to represent entity relationships.

Hint 4: Tools/Debugging Print out entity chains for a few faces to confirm traversal.

Books That Will Help

Topic Book Chapter
STEP overview “Geometric Modeling” by Michael E. Mortenson Ch. 14
B-Rep mapping “Geometric Modeling” by Michael E. Mortenson Ch. 10
Parsing fundamentals “Compilers: Principles, Techniques, and Tools” by Aho et al. Ch. 4

Implementation Hints

  • Keep the parser read-only: no need to write STEP files.
  • Build a small entity whitelist and expand gradually.
  • Provide a JSON output for inspection and debugging.

Learning Milestones

  1. First milestone: You can parse and list STEP entities.
  2. Second milestone: You can resolve basic geometry references.
  3. Final milestone: You can explain how STEP enables CAD exchange.