Motus Reference Manual
Page 14 of 146
Version 1.1
29/11/2019
positive rotation on that axis.
5.6.2
Rotation Order
When multiple axes are rotated, to imagine the final orientation the three rotations
must be performed in the order heading first, then pitch and then roll. To deduce the
final orientation the unit should first be considered level with the X axis pointing north
and the Z axis pointing down. Heading is applied first, then pitch is applied and finally
roll is applied to give the final orientation. This can be hard for some people to grasp
at first and is often best learned experimentally by rotating Motus with your hand
whilst watching the orientation plot in real time on the computer.
5.7
Geodetic Co-ordinate System
The geodetic co-ordinate system is the most popular way of describing an absolute
position on the Earth. It is made up of the angles latitude and longitude combined with
a height relative to the ellipsoid. Latitude is the angle that specifies the north to south
position of a point on the Earth's surface. Longitude is the angle that specifies the east
to west position of a point on the Earth's surface. The line of zero latitude is the
equator and the line of zero longitude is the prime meridian. Illustration 4 shows how
latitude and longitude angles are used to describe a position on the surface of the
Earth.
Illustration 3: Second right hand rule
