graphs: add Attitude/Circular Angle Error

Author: peterbarker

Diff for: MAVProxy/tools/graphs/mavgraphs.xml

@@ -49,6 +49,11 @@
     <expression>degrees(sqrt(ATTITUDE.roll*ATTITUDE.roll+ATTITUDE.pitch*ATTITUDE.Pitch))</expression>
   </graph>
 
+  <graph name='Attitude/Circular Angle Error'>
+  <description>Difference between total circular angle, as limited by ANGLE_MAX in Copter, and desired circular angle.</description>
+    <expression>sqrt(((ATT.Roll-ATT.DesRoll)**2)+((ATT.Pitch-ATT.DesPitch)**2))</expression>
+  </graph>
+
   <graph name='Sensors/Accelerometer/Accelerometers'>
     <description>Accelerometer Output</description>
     <expression>RAW_IMU.xacc*9.81*0.001 RAW_IMU.yacc*9.81*0.001 RAW_IMU.zacc*9.81*0.001 gravity(RAW_IMU)</expression>