From 74cb35d3acc9f1f5526c1d7cdb77643d2584b496 Mon Sep 17 00:00:00 2001
From: yuni <hut@hut.pm>
Date: Thu, 28 Nov 2024 01:39:53 +0100
Subject: [PATCH] atmosphere: update pressure regression

---
 doc/research.md | 10 ++++++----
 src/nature.rs   | 18 +++++++++---------
 2 files changed, 15 insertions(+), 13 deletions(-)

diff --git a/doc/research.md b/doc/research.md
index b16f748..ae85058 100644
--- a/doc/research.md
+++ b/doc/research.md
@@ -105,10 +105,12 @@ Based on Table 8 from SRC1:
 
 ### Regression analysis
 
-- 350km-850km: `p[bar](a[m]) = e^(-8.0920583983 - 0.0000066339143 * a)`
-- 50km-350km: `p[bar](a[m]) = e^(-0.969198983 - 0.000027000953 * a)`
-- -125km-50km: `p[bar](a[m]) = e^(0.0626589359 - 0.0000473755348 * a)`
-- <-125km: `p[bar](a[m]) = -0.7155577817531 * a - 89044.7227191413` (low-effort linear regression assuming p(-70000km) = 5e7 bar)
+Pressure:
+
+- 500km-1029.2km: `p[bar](x[m]) = exp(-13.3961516218 - 0.0000071595 * x)`
+- 200km-500km: `p[bar](x[m]) = exp(-3.4340885227 - 0.0000277865 * x)`
+- 0km-200km: `p[bar](x[m]) = exp(-0.0020248515 - 0.0000454102 * x)`
+- <0km: `p[bar](x[m]) = -(1.45773e-16) * x^3 + 1` (low-effort cubic regression on `[(-70000km, 50Mbar), (0m, 1bar)]`)
 
 ### Designing the in-game atmosphere
 
diff --git a/src/nature.rs b/src/nature.rs
index 08a99bb..5350d48 100644
--- a/src/nature.rs
+++ b/src/nature.rs
@@ -289,15 +289,15 @@ pub fn format_seconds_to_hour_min(seconds: f64) -> String {
 
 pub fn jupiter_altitude_to_pressure(altitude: f64) -> f64 {
     // See doc/research.md
-    let a = altitude - JUPITER_RADIUS;
-    if a >= 1e6 {
+    let x = altitude - JUPITER_RADIUS;
+    if x >= 1030e3 {
         return 0.0;
-    } else if a >= 350e3 {
-        return (-8.0920583983 - 0.0000066339143 * a).exp();
-    } else if a >= 50e3 {
-        return (-0.969198983 - 0.000027000953 * a).exp();
-    } else if a >= -125e3 {
-        return (0.0626589359 - 0.0000473755348 * a).exp();
+    } else if x >= 500e3 {
+        return (-13.3961516218 - 0.0000071595 * x).exp();
+    } else if x >= 200e3 {
+        return (-3.4340885227 - 0.0000277865 * x).exp();
+    } else if x >= 0.0 {
+        return (-0.0020248515 - 0.0000454102 * x).exp();
     }
-    return -0.7155577817531 * a - 89044.7227191413;
+    return -(1.45773e-16) * x.powf(3.0) + 1;
 }