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Outline Versus Centreline

Status: Current geometry doctrine

Authority: Current contract (2026-08-12) and vectorization handover practice

Last reviewed: 2026-08-14

Question

Why are traced ink boundaries not engineering lines?

Short answer

An outline follows the boundary of ink. A centreline follows the stroke middle. Drawing Lab must convert outlines before treating them as engineering carriers.

What we tried

Potrace recipe potrace-0.80 produced closed appearance outlines. Inkscape four-scan produced sharp-dark multi-scan appearance benchmarks. Ridge detection produced ridge pixels, ridge paths, and ridge vectors. Vector Lines recovered centrelines from Potrace-derived fill.

Why outlines helped

Outlines give fast appearance review. They preserve visible ink shape for human comparison. Potrace remains a fallback appearance baseline. Inkscape four-scan remains a useful sharp-dark benchmark.

Why outlines failed as engineering lines

Outline boundaries are not centrelines. Using outlines directly invents double edges and false carriers. The current contract forbids treating Inkscape or Potrace outline boundaries as engineering lines before centreline conversion.

What we retained

  • Potrace potrace-0.80 as fallback appearance evidence
  • Inkscape four-scan as optional appearance benchmark
  • Ridge centreline evidence where available
  • Centreline recovery for Dimensions from Vector Lines
  • Deep method detail in Vectorization

Naming note

potrace-0.80 is the recipe and threshold name. The Potrace engine version in the Detection worktree is Potrace 1.16. User-facing prose uses centreline and centrelines.

Open Questions

  • Which centreline recovery method becomes the default for Detected Sheet geometry layers?

Sources