search

johanley / planisphere

Generate a precise, customizable planisphere as two PDF files (a star chart and a transparency).
2 stars 0 forks source link

Stray constellation line crossing the full chart, for year -2796 #6

Closed johanley closed 2 years ago

johanley commented 2 years ago

Latitude 46.0, longitude -63.0. Visible in this range of years: -2755..-2835 (approx). Straight line moves across the map from 4 o'clock to 10 o'clock.

johanley commented 2 years ago

Expanding the list of stars, to filter only by mag and not geometry, has no effect.

johanley commented 2 years ago

Could it be bad data, in the arrays that define the constellation lines? Reducing the ChartUtils.EDGE_OVERLAP_DEGREES setting from 60 to 58 removes the problem!

Reducing ChartUtils.EDGE_OVERLAP_DEGREES works for the present case, but it's a workaround that doesn't address the core bug.

The behavior seems to be consistent with the south celestial pole moving between a pair of stars connected by a constellation-line. In that case, the pair will have wildly different right ascensions. The data in that case is correct, but the algo is defective.

johanley commented 2 years ago

starchart-2796-N.pdf

johanley commented 2 years ago

starchart-2770.pdf

johanley commented 2 years ago

starchart-south-pole-on-a-line.pdf Look at the south pole for -2796. It's exactly on a line joining two stars in Hydrus. That's the explanation.

johanley commented 2 years ago

The code now abandons any lines that would cross the whole chart if drawn. (Constellations.java)