Convention kinematic tools

Hi all,

I would like to know if there is a convention for the sign of the angular velocity value calculated from the the kinematic tool? Sometime the value is negative but I cannot make any correlation with my model.



Hi Paul,

The short answer is it’s a bit arbitrary at the moment. So I’ve just now changed it to always return a positive angle.

Until now the sign was positive when the rotation is counter-clockwise around the stage rotation ‘pole’ (and negative if clockwise). The stage rotation is what generates the angular velocity (vector) at a position on the globe. However a particular stage rotation can be represented by two different stage rotation ‘pole’ and ‘angle’ pairs, where one pair is the negation of the other pair (ie, if you negate or flip the pole, and also negate the angle, you’ll get the exact same stage rotation). So in this sense the stage rotation ‘pole’ could be either of two opposite pointing poles, which is why the angular velocity angle was sometimes negative. Note that this doesn’t affect the velocity ‘vector’ though (ie, you’ll always get the exact same velocity ‘vector’ regardless of which pole/angle pair you use). So values obtained from the velocity ‘vector’ like the azimuth, colat and lon are not affected by this pole/angle duality.

Also note that the kinematic graph had always displayed the angular velocity as an absolute value (ie, positive) anyway, so now we’re just making the values in the table reflect that (ie, always positive, unlike in the screenshot below)…


Thanks for the reply, John.