Mercator/Mollweide projections and spherical arena visualization

[mbreiser]

Summary

Now that spherical geometry is fully implemented in the web pattern generator, add visualization capabilities that show how patterns map onto the fly's visual field.

Features (each independently toggleable)

1. Map Projections

• Mercator projection view of arena pattern
• Mollweide projection view of arena pattern
• These provide familiar 2D representations of the spherical mapping

2. 3D Spherical Arena Visualization

• Project LED coordinates (or disc representations of LEDs) onto a unit sphere that circumscribes the cylindrical arena
• Shows true geometric understanding of how patterns map onto the fly's visual field
• Integrate fly FOV data from existing datasets

3. Ray-Trace Overlay

• Cast rays from arena center through individual LED positions outward to the circumscribing sphere surface
• Extend the existing 3D direction-vector visualization
• Display subsets of rays to keep the visualization readable (e.g., one panel at a time, or every Nth ray)

Goal

Move from showing a single summary vector to showing the full spherical pattern distribution, making the arena-to-visual-field mapping intuitive and inspectable.

Implementation Notes

• Builds on existing spherical geometry (arena-geometry.js) and 3D viewer (Three.js)
• MATLAB PatternPreviewerApp already has Mercator/Mollweide views — can use as reference
• Each visualization should have a toggle checkbox/button
• Consider performance for large arenas (G6 3×18 = 1080 panels × 400 LEDs = 432K rays)