Revert the MTK GPS driver to only claiming a fix when the GPS has a 3D solution, per discussion with Paul.

libraries/AP_GPS/AP_GPS_MTK.cpp

@@ -130,11 +130,7 @@ restart:
 void 
 AP_GPS_MTK::_parse_gps(void)
 {
-	if (_buffer.msg.fix_type-1 >= 1){
-		fix = true;
-	} else {
-		fix = false;
-	}
+	fix				= (_buffer.msg.fix_type == FIX_3D);
 	latitude		= _swapl(&_buffer.msg.latitude)  * 10;
 	longitude		= _swapl(&_buffer.msg.longitude) * 10;
 	altitude		= _swapl(&_buffer.msg.altitude);

libraries/AP_GPS/GPS.cpp

@@ -4,13 +4,9 @@
 #include "WProgram.h"
 #include <stdio.h>
 
-void
-GPS::_setTime(void){
-	_lastTime = millis();
-}
-
 int
-GPS::status(void){
+GPS::status(void)
+{
 	if (millis() - _lastTime >= 500){
 		return 0;
 	} else if (fix == 0) {
@@ -20,6 +16,12 @@ GPS::status(void){
 	}
 }
 
+void
+GPS::_setTime(void)
+{
+	_lastTime = millis();
+}
+
 void
 GPS::_error(const char *fmt, ...)
 {

libraries/AP_GPS/GPS.h

@@ -31,6 +31,8 @@ public:
 	/// This routine performs any one-off initialisation required to set the
 	/// GPS up for use.
 	///
+	/// Must be implemented by the GPS driver.
+	///
 	/// @param	s	Stream connected to the GPS module.  If NULL, assumed to
 	///				have been set up at constructor time.
 	///
@@ -40,8 +42,23 @@ public:
 	///
 	/// This routine must be called periodically to process incoming data.
 	///
+	/// Must be implemented by the GPS driver.
+	///
 	virtual void	update(void) = 0;
 
+	/// Query GPS status
+	///
+	/// The 'valid message' status indicates that a recognised message was
+	/// received from the GPS within the last 500ms.
+	///
+	/// @todo should probably return an enumeration here.
+	///
+	/// @return	0			No GPS connected/detected
+	/// @return 1			Receiving valid GPS messages but no lock
+	/// @return 2			Receiving valid messages and locked
+	///
+	int				status(void);
+
 	// Properties
 	long	time;			///< GPS time in milliseconds from the start of the week
 	long	latitude;		///< latitude in degrees * 10,000,000
@@ -51,20 +68,26 @@ public:
 	long	ground_course;	///< ground course in 100ths of a degree
 	long	speed_3d;		///< 3D speed in cm/sec (not always available)
 	uint8_t num_sats;		///< Number of visible satelites
-	bool	fix;			///< true if we have a position fix
-	
+
 	/// Set to true when new data arrives.  A client may set this
 	/// to false in order to avoid processing data they have
 	/// already seen.
 	bool	new_data;
-	bool	valid_read;
 
-	int	status(void);		///< 0 = Not Connected, 1 = Receiving Valid Messages but No Lock, 2 = Locked
+	// Deprecated properties
+	bool	fix;			///< true if we have a position fix (use ::status instead)
+	bool	valid_read;		///< true if we have seen data from the GPS (use ::status instead)
 
+	// Debug support
 	bool	print_errors; 	///< if true, errors will be printed to stderr
 
 protected:
-	Stream	*_port;			///< stream port the GPS is attached to
+	Stream	*_port;				///< stream port the GPS is attached to
+	unsigned long _lastTime;	///< Timer for lost connection
+
+	/// reset the last-message-received timer used by ::status
+	///
+	void	_setTime(void);
 
 	/// perform an endian swap on a long
 	///
@@ -74,10 +97,6 @@ protected:
 	///
 	long	_swapl(const void *bytes);
 
-	unsigned long _lastTime;	///< Timer for lost connection
-
-	void	_setTime(void);
-
 	/// perform an endian swap on an int
 	///
 	/// @param	bytes		pointer to a buffer containing bytes representing an