From bc7f811ff04f2d7b47cc2662d575b77b33a5dd7c Mon Sep 17 00:00:00 2001
From: Andrew Tridgell <andrew@tridgell.net>
Date: Thu, 28 Nov 2019 13:41:29 +1100
Subject: [PATCH] AP_GPS: cope with UAVCAN GPS that don't provide Aux message

thanks to @VadimZ for the suggestion
---
 libraries/AP_GPS/AP_GPS_UAVCAN.cpp | 14 ++++++++++++++
 libraries/AP_GPS/AP_GPS_UAVCAN.h   |  1 +
 2 files changed, 15 insertions(+)

diff --git a/libraries/AP_GPS/AP_GPS_UAVCAN.cpp b/libraries/AP_GPS/AP_GPS_UAVCAN.cpp
index f4f9a68f5d..80d58faf0e 100644
--- a/libraries/AP_GPS/AP_GPS_UAVCAN.cpp
+++ b/libraries/AP_GPS/AP_GPS_UAVCAN.cpp
@@ -240,6 +240,12 @@ void AP_GPS_UAVCAN::handle_fix_msg(const FixCb &cb)
         interim_state.num_sats = 0;
     }
 
+    if (!seen_aux) {
+        // if we haven't seen an Aux message then populate vdop and
+        // hdop from pdop. Some GPS modules don't provide the Aux message
+        interim_state.hdop = interim_state.vdop = cb.msg->pdop * 100.0;
+    }
+
     interim_state.last_gps_time_ms = AP_HAL::millis();
 
     _new_data = true;
@@ -336,6 +342,12 @@ void AP_GPS_UAVCAN::handle_fix2_msg(const Fix2Cb &cb)
         interim_state.num_sats = 0;
     }
 
+    if (!seen_aux) {
+        // if we haven't seen an Aux message then populate vdop and
+        // hdop from pdop. Some GPS modules don't provide the Aux message
+        interim_state.hdop = interim_state.vdop = cb.msg->pdop * 100.0;
+    }
+    
     interim_state.last_gps_time_ms = AP_HAL::millis();
 
     _new_data = true;
@@ -355,10 +367,12 @@ void AP_GPS_UAVCAN::handle_aux_msg(const AuxCb &cb)
     WITH_SEMAPHORE(sem);
 
     if (!uavcan::isNaN(cb.msg->hdop)) {
+        seen_aux = true;
         interim_state.hdop = cb.msg->hdop * 100.0;
     }
 
     if (!uavcan::isNaN(cb.msg->vdop)) {
+        seen_aux = true;
         interim_state.vdop = cb.msg->vdop * 100.0;
     }
 }
diff --git a/libraries/AP_GPS/AP_GPS_UAVCAN.h b/libraries/AP_GPS/AP_GPS_UAVCAN.h
index 32c636dfa2..6e1607ef6d 100644
--- a/libraries/AP_GPS/AP_GPS_UAVCAN.h
+++ b/libraries/AP_GPS/AP_GPS_UAVCAN.h
@@ -65,6 +65,7 @@ private:
 
     bool seen_message;
     bool seen_fix2;
+    bool seen_aux;
 
     // Module Detection Registry
     static struct DetectedModules {