From 5d22115787dc91d912e90d5f45a718dce3a76d46 Mon Sep 17 00:00:00 2001
From: Alexander Keller <makeller1@utexas.edu>
Date: Wed, 31 May 2023 09:48:50 -0700
Subject: [PATCH] AP_GPS:Comform to ardupilot undulation definition

---
 libraries/AP_GPS/AP_GPS_SBF.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libraries/AP_GPS/AP_GPS_SBF.cpp b/libraries/AP_GPS/AP_GPS_SBF.cpp
index 4da9e4e418..5119786f27 100644
--- a/libraries/AP_GPS/AP_GPS_SBF.cpp
+++ b/libraries/AP_GPS/AP_GPS_SBF.cpp
@@ -417,7 +417,7 @@ AP_GPS_SBF::process_message(void)
             state.location.lng = (int32_t)(temp.Longitude * RAD_TO_DEG_DOUBLE * (double)1e7);
             state.location.alt = (int32_t)(((float)temp.Height - temp.Undulation) * 1e2f);
             state.have_undulation = true;
-            state.undulation = temp.Undulation;
+            state.undulation = -temp.Undulation;
         }
 
         if (temp.NrSV != 255) {