Initial Commit

backend/src/astronomy/horizon.rs

@@ -0,0 +1,33 @@
+use serde::{Deserialize, Serialize};
+
+#[derive(Debug, Clone, Serialize, Deserialize, sqlx::FromRow)]
+pub struct HorizonPoint {
+    pub az_deg: i32,
+    pub alt_deg: f64,
+}
+
+/// Linear interpolation of horizon altitude at a given azimuth.
+/// The profile must have points at every integer degree 0–359.
+pub fn horizon_alt(az_deg: f64, profile: &[HorizonPoint]) -> f64 {
+    if profile.is_empty() {
+        return 15.0;
+    }
+
+    let az = az_deg.rem_euclid(360.0);
+    let lo_idx = az.floor() as usize % 360;
+    let hi_idx = (lo_idx + 1) % 360;
+    let frac = az.fract();
+
+    let lo_alt = profile
+        .iter()
+        .find(|p| p.az_deg == lo_idx as i32)
+        .map(|p| p.alt_deg)
+        .unwrap_or(15.0);
+    let hi_alt = profile
+        .iter()
+        .find(|p| p.az_deg == hi_idx as i32)
+        .map(|p| p.alt_deg)
+        .unwrap_or(15.0);
+
+    lo_alt + frac * (hi_alt - lo_alt)
+}