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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.
Real estate firm decided to rewrite the building design system from C# to Java.
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 floating-point 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. Could not get straight skeletons working under time pressure. Wrote
a custom solver that fixed invalid loops by backtracking instead.
Problem of finding the largest inscribed rectangle was surprisingly difficult.
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 proved numerically incompatible with Rhino. Replaced BSP trees
with vector-based primitives and JBLAS instead.
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