From f381ef93e886152ce5e1b5f2bd70067ac66353a6 Mon Sep 17 00:00:00 2001
From: Jonathan Challinger <mr.challinger@gmail.com>
Date: Tue, 28 Apr 2015 11:15:49 -0700
Subject: [PATCH] AP_Baro: add get_air_density_ratio

---
 libraries/AP_Baro/AP_Baro.cpp | 6 ++++++
 libraries/AP_Baro/AP_Baro.h   | 3 +++
 2 files changed, 9 insertions(+)

diff --git a/libraries/AP_Baro/AP_Baro.cpp b/libraries/AP_Baro/AP_Baro.cpp
index 45f7c27385..f412fe4f5b 100644
--- a/libraries/AP_Baro/AP_Baro.cpp
+++ b/libraries/AP_Baro/AP_Baro.cpp
@@ -208,6 +208,12 @@ float AP_Baro::get_EAS2TAS(void)
     return _EAS2TAS;
 }
 
+// return air density / sea level density - decreases in altitude
+float AP_Baro::get_air_density_ratio(void)
+{
+    return 1.0f/(sq(get_EAS2TAS()));
+}
+
 // return current climb_rate estimeate relative to time that calibrate()
 // was called. Returns climb rate in meters/s, positive means up
 // note that this relies on read() being called regularly to get new data
diff --git a/libraries/AP_Baro/AP_Baro.h b/libraries/AP_Baro/AP_Baro.h
index 91f9bee174..6a0eed037b 100644
--- a/libraries/AP_Baro/AP_Baro.h
+++ b/libraries/AP_Baro/AP_Baro.h
@@ -79,6 +79,9 @@ public:
     // get scale factor required to convert equivalent to true airspeed
     float get_EAS2TAS(void);
 
+    // get air density / sea level density - decreases in altitude
+    float get_air_density_ratio(void);
+
     // get current climb rate in meters/s. A positive number means
     // going up
     float get_climb_rate(void);