Module: AstroChart::Synastry

Defined in:
lib/astro_chart/synastry.rb

Overview

Synastry (合盤): cross-chart comparison between two natal charts.

Pure composition of existing modules — Aspects.calculate works on any two ecliptic longitudes regardless of which chart they come from, and Houses.find_house places any longitude into any set of cusps. Backend-independent: no ephemeris call happens here.

Typical usage with two Chart#generate results:

result = Synastry.between(chart_a, chart_b)
result["aspects"]               # A 的行星 × B 的行星 的跨盤相位
result["a_planets_in_b_houses"] # A 的行星落在 B 的哪一宮（疊盤）
result["b_planets_in_a_houses"] # B 的行星落在 A 的哪一宮

Constant Summary collapse

BODIES =

Bodies used for cross-chart comparison. 南交點 is excluded by default: it is always exactly opposite 北交點, so including it would mirror every node aspect and double the noise.

Ephemeris::PLANETS.keys.freeze

Class Method Summary collapse

Class Method Details

.between(chart_a, chart_b, orb_limit: nil) ⇒ Object

Full synastry between two Chart#generate result hashes.



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# File 'lib/astro_chart/synastry.rb', line 68

def self.between(chart_a, chart_b, orb_limit: nil)
  pos_a = positions_from_chart(chart_a)
  pos_b = positions_from_chart(chart_b)
  cusps_a = cusps_from_chart(chart_a)
  cusps_b = cusps_from_chart(chart_b)

  {
    "aspects"               => cross_aspects(pos_a, pos_b, orb_limit: orb_limit),
    "a_planets_in_b_houses" => house_overlay(pos_a, cusps_b),
    "b_planets_in_a_houses" => house_overlay(pos_b, cusps_a),
  }
end

.cross_aspects(positions_a, positions_b, orb_limit: nil) ⇒ Object

Cross aspects between two position sets.

positions_a / positions_b: { "太陽" => 123.45, ... } (ecliptic longitudes) orb_limit: optional Float — keep only aspects with orb <= limit. (Aspects uses natal orbs: conjunction 15°, others 6-10°. Synastry practice often uses tighter orbs; pass e.g. orb_limit: 6.0 to tighten.)

Returns Array of:

{ "a_planet" => "太陽", "b_planet" => "月亮",
"aspect_type" => "三分相", "orb" => 1.23 }

Note: (A太陽, B月亮) and (A月亮, B太陽) are different pairs — they compare different positions, both are kept.



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# File 'lib/astro_chart/synastry.rb', line 34

def self.cross_aspects(positions_a, positions_b, orb_limit: nil)
  results = []
  positions_a.each do |name_a, pos_a|
    positions_b.each do |name_b, pos_b|
      aspect_type, orb = Aspects.calculate(pos_a, pos_b)
      next if aspect_type.nil?
      next if orb_limit && orb > orb_limit

      results << {
        "a_planet"    => name_a,
        "b_planet"    => name_b,
        "aspect_type" => aspect_type,
        "orb"         => orb,
      }
    end
  end
  results.sort_by { |r| r["orb"] }
end

.cusps_from_chart(chart) ⇒ Object

Extract the 12 cusp degrees (index 0 = 1st house) from a Chart#generate hash.

Raises:

  • (ArgumentError) 


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# File 'lib/astro_chart/synastry.rb', line 97

def self.cusps_from_chart(chart)
  houses = chart&.dig("chart", "houses")
  raise ArgumentError, "chart has no houses data" if houses.nil? || houses.length != 12

  houses.sort_by { |h| h["house_number"] }.map { |h| h["degree"] }
end

.house_overlay(positions, cusps) ⇒ Object

House overlay (疊盤): place one person's planets into the other person's houses.

positions: { "太陽" => 123.45, ... } cusps: 12 house cusp degrees (cusps = 1st house)

Returns { "太陽" => 7, ... } (house number 1-12)



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# File 'lib/astro_chart/synastry.rb', line 60

def self.house_overlay(positions, cusps)
  positions.each_with_object({}) do |(name, pos), out|
    house = Houses.find_house(pos, cusps)
    out[name] = house if house
  end
end

.positions_from_chart(chart) ⇒ Object

Extract { name => total_degree } for BODIES from a Chart#generate hash. Ruler points appended by key_points_data are ignored (not in BODIES).

Raises:

  • (ArgumentError) 


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# File 'lib/astro_chart/synastry.rb', line 83

def self.positions_from_chart(chart)
  planets = chart&.dig("chart", "planets")
  raise ArgumentError, "chart has no planets data" if planets.nil? || planets.empty?

  planets.each_with_object({}) do |p, out|
    name = p["planet"]
    next unless BODIES.include?(name)

    degree = p["total_degree"] || total_degree_from(p)
    out[name] = degree if degree
  end
end