Draw gray-line terminator as a smooth analytic band#136
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Old drawGrayLine() built the twilight zone by sweeping a 2-degree
lat/lon grid for points where |solar altitude| < 6 deg, then bucketing
them into 5-degree latitude bands and emitting one rectangle per
band+segment. The result rendered as a stack of 10-degree-tall
rectangles -- a visible staircase along the terminator on the map.
Replace with a closed-form solve. For each longitude, solve
sin(alpha) = sin(decl)*sin(lat) + cos(decl)*cos(HA)*cos(lat)
= R * sin(lat + phi)
for alpha = +/-6 deg, giving the day-edge and night-edge latitude
of the civil-twilight band. Walk longitude west-to-east to build the
day edge, east-to-west to close the night edge, and render the result
as a single L.polygon. No bucketing, no rectangles, no staircase.
Sweep at 1-degree longitude steps (361 vertices per edge) for a
smooth curve at the price of a single L.polygon instead of dozens of
small ones, so total draw cost is comparable.
served.html kept in sync with dashboard.html.
https://claude.ai/code/session_01BLfWHK9hf8k4aBBaQjfQa8
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Summary
Replace the staircase rendering of the gray-line terminator band with a smooth analytic curve.
The previous
drawGrayLine()swept a 2° lat/lon grid for points where|solar altitude| < 6°, then bucketed those points into 5°-wide latitude bands and emitted one rectangle per (band, longitude segment). Because each rectangle was 10° tall (lat ± 5), the resulting band rendered as a stack of vertically-aligned rectangles — visibly stairsteppy where the terminator runs diagonally, with extra blocky artifacts wherever a band's longitudes had a gap > 10°.This rewrites it in closed form. For each longitude, solve
where
R = √(sin²δ + cos²δ·cos²HA)andφ = atan2(cos(δ)·cos(HA), sin(δ)). Thenlat = asin(sin(α)/R) − φ, clamped to[−90°, 90°]. Compute this at α = +6° (day edge) and α = −6° (night edge) for every 1° of longitude, then build a single closed polygon by walking the day edge west→east and the night edge east→west. No grid sweep, no bucketing, no rectangles.served.htmlkept in sync withdashboard.html.Test plan
node --checkparses the inlined dashboard JS cleanlydiff src/dvoacap/dashboard/dashboard.html served.htmlis emptyhttps://claude.ai/code/session_01BLfWHK9hf8k4aBBaQjfQa8
Generated by Claude Code