Myriahedral reconstruction artifacts

These files preserve the temporary inputs, generators, selected topology, and verification outputs used to implement src.projections/cart0freak0-myriahedral.h. They were copied byte-for-byte from /tmp/myriaworld.gjlN58 on 2026-08-01.

Repository location

The reconstruction package was staged in a temporary ad-hoc area during development and now lives permanently in assets.static/myriahedral. Documentation, tooling, and future provenance references should use the permanent path. The production base raster remains assets.static/myriahedral/black-white-downsampled.png, alongside these supporting artifacts.

Selected configuration

Grid entry 37 in boost-grid-configs.txt records:

wlat = 0.5
wlon = 0.1
clat = -60
clon = -65

These are legacy option names, not semantic latitude/longitude labels. In boost_tree.cc, wlat weights longitude distance, wlon weights latitude distance, clat is the effective center longitude, and clon is the effective center latitude. The selected effective center is consequently (-60, -65) in (longitude, latitude) order.

The grid was generated after Gaussian smoothing with sigma = 0.7. The selected planar registration applies a final 335 degree rotation. The rotation is used by the projection header and landmark scoring; it is not baked into boost-grid-37.tree or the unrotated coordinates in boost-grid-37.npz.

Files

File	Role
`exact-fractions.txt`	Exact land fraction, spherical area, centroid, and special-country bits for each of 5120 faces
`exact_fraction.cc`	S2-based program that generated the exact face data
`export_countries.py`	Historical Natural Earth polygon exporter used before exact face intersection
`boost_tree.cc`	Boost.Graph smoothing, weighting, Prim-tree, and grid generator
`boost-grid-configs.txt`	Parameter map for the generated candidate grid
`boost-grid-37.tree`	Selected parent tree; direct source of the compact hexadecimal data in the production header
`reconstruct.py`	Historical independent reconstruction of the legacy mesh, affine/chord projection, and rendering lineage
`render_grid.py`	Converts generated tree files into independent planar `.npz` layouts
`boost-grid-37.npz`	Selected unrotated legacy planar baseline used during tree and registration reconstruction
`landmark_scores.py`	Geographic-anchor registration scorer
`landmark-output.txt`	Scoring output; grid 37 selects the 335-degree orientation
`grid37-land.png`	Final low-resolution diagnostic rendering of the selected layout
`perspective-configurations.json`	Machine-readable reference and five-perspective preprocessing, registration, digest, and artifact metadata
`SHA256SUMS`	Digests for every preserved artifact except this manifest

The scripts intentionally retain the absolute /tmp/myriaworld.gjlN58 paths with which they were run. Adjust those paths before rerunning them elsewhere. Large dependency trees, compiler outputs, the cloned upstream repository, historical Natural Earth source files, and rejected candidate layouts are not duplicated here. Their derived data needed by the final implementation is captured by exact-fractions.txt, the selected tree, and the legacy planar baseline.

The five exploratory trees are embedded under src.generate/ and selected by cart0freak0-myriahedral-perspectives.h. They reuse the exact fractions and historical weighting program recorded here; their complete parameters, raw bounds, rotations, parent-data paths, and source-tree digests are recorded in perspective-configurations.json.

Numerical lineage and production divergence

The preserved scripts and boost-grid-37.npz reproduce the historical myriaworld numerical lineage. They remain authoritative for preprocessing, terminal-face numbering, the selected spanning tree, and landmark registration. They are not the numerical oracle for the current C++ forward projection.

A 2026-08-04 audit found that the legacy face-local transform was an orthogonal chord-plane approximation rather than van Wijk’s central gnomonic mapping. It introduced a small false discontinuity across retained hinges. The inherited seed-triangle formula also mixed two edge lengths, and its base icosahedron constants were truncated. The production implementation now:

derives and normalizes the regular-icosahedron vertices from the golden ratio while retaining face order;
embeds the layout seed with a signed, length-preserving dot-product construction;
maps points with widened central gnomonic barycentric coordinates; and
uses containment-first widened predicates plus roundoff-bounded validation.

Consequently, current raw bounds and fixed geographic anchors intentionally differ slightly from boost-grid-37.npz and the reference raster’s generating algorithm. Schema v2 of perspective-configurations.json records the current bounds, distinguishes Prim root face 103 from layout seed face 0, and names the gnomonic method. The raster remains a subpixel registration and visual reference, not proof of the forward formula.