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title: Geometry kernel for building design
date: 2022-07-31
layout: post
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Written in 2026, backdated to 2022.

Joined real estate firm mid-migration from C# to Java. Lacking a geometry
kernel, the project had stalled.

Building geometries are small—mostly 2D. No frame budgets or low-latency
constraints. Numerical parity with Rhino was mandatory. Architects and
structural engineers supplied test cases and tolerances.

Implemented polygon clipping with Sutherland–Hodgman. No drama.

Fortune's algorithm was a missed opportunity. Implemented the beach line using
a linear list instead of the balanced binary tree. Planned to return to this.
Never had the chance.

Z and H-shaped floor plan offsets produced self-intersections that even Rhino
mishandled. Couldn't implement straight skeletons under time pressure.  Wrote a
custom solver that fixed invalid loops by backtracking instead.

Problem of finding the largest inscribed rectangle surprised me. No single
algorithm covered both convex and concave shapes. Brute-force grid search
yielded 12% more buildable area—but not the true optimum.

Java BSP library produced results numerically incompatible with Rhino's.
Replaced BSP trees with vector-based primitives and JBLAS.

Migration resumed.