mavflightview.py: correct plotting of GPS data

the "type" variable was being over-written to include the instance number before we dropped down through the code which specially-treats messages based on the type variable.

So stop overwriting the variable before that switch statement, create a special string for when we need it.

Visible difference with this PR is that the GPS plots on the map no longer have lines starting from 0,0 if the GPS starts with no fix.

MAVProxy/tools/mavflightview.py

@@ -384,6 +384,7 @@ def mavflightview_mav(mlog, options=None, flightmode_selections=[]):
             # may only be present for colour-source expressions to work
             continue
 
+        type_with_instance = type
         try:
             # remember that "m" here might be a mavlink message.
             instance_field = m.fmt.instance_field
@@ -393,7 +394,7 @@ def mavflightview_mav(mlog, options=None, flightmode_selections=[]):
                 ):
                 continue
 
-            type = '%s[%u]' % (type, m_instance_field_value)
+            type_with_instance = '%s[%u]' % (type, m_instance_field_value)
         except Exception:
             pass
 
@@ -473,11 +474,11 @@ def mavflightview_mav(mlog, options=None, flightmode_selections=[]):
                 continue
 
             # automatically add new types to instances
-            if type not in instances:
-                instances[type] = len(instances)
+            if type_with_instance not in instances:
+                instances[type_with_instance] = len(instances)
                 while len(instances) >= len(path):
                     path.append([])
-            instance = instances[type]
+            instance = instances[type_with_instance]
 
             # only plot thing we have a valid-looking location for:
             if abs(lat)<=0.01 and abs(lng)<=0.01:
@@ -490,8 +491,8 @@ def mavflightview_mav(mlog, options=None, flightmode_selections=[]):
             tdays = grapher.timestamp_to_days(m._timestamp)
             point = (lat, lng, colour, tdays)
 
-            if options.rate == 0 or not type in last_timestamps or m._timestamp - last_timestamps[type] > 1.0/options.rate:
-                last_timestamps[type] = m._timestamp
+            if options.rate == 0 or not type_with_instance in last_timestamps or m._timestamp - last_timestamps[type_with_instance] > 1.0/options.rate:
+                last_timestamps[type_with_instance] = m._timestamp
                 path[instance].append(point)
     if len(path[0]) == 0:
         print("No points to plot")