lib/sensor_calibration: BiasCorrectedSensorOffset() don't incorporate thermal offsets

- the thermal offsets are an optional correction applied to the raw data, so when updating an existing calibration offset with new learned bias we don't want this incorporated

src/lib/sensor_calibration/Accelerometer.hpp

@@ -87,7 +87,8 @@ public:
 	// Compute sensor offset from bias (board frame)
 	matrix::Vector3f BiasCorrectedSensorOffset(const matrix::Vector3f &bias) const
 	{
-		return (_rotation.I() * bias).edivide(_scale) + _thermal_offset + _offset;
+		// updated calibration offset = existing offset + bias rotated to sensor frame and unscaled
+		return _offset + (_rotation.I() * bias).edivide(_scale);
 	}
 
 	bool ParametersLoad();

src/lib/sensor_calibration/Gyroscope.hpp

@@ -91,7 +91,8 @@ public:
 	// Compute sensor offset from bias (board frame)
 	matrix::Vector3f BiasCorrectedSensorOffset(const matrix::Vector3f &bias) const
 	{
-		return (_rotation.I() * bias) + _thermal_offset + _offset;
+		// updated calibration offset = existing offset + bias rotated to sensor frame
+		return _offset + (_rotation.I() * bias);
 	}
 
 	bool ParametersLoad();

src/lib/sensor_calibration/Magnetometer.hpp

@@ -89,7 +89,8 @@ public:
 	// Compute sensor offset from bias (board frame)
 	matrix::Vector3f BiasCorrectedSensorOffset(const matrix::Vector3f &bias) const
 	{
-		return _scale.I() * _rotation.I() * bias + _offset;
+		// updated calibration offset = existing offset + bias rotated to sensor frame and unscaled
+		return _offset + (_scale.I() * _rotation.I() * bias);
 	}
 
 	bool ParametersLoad();