A little confused about the heading definition

As the doc shows, Heading is the rotation about the negative z axis. Pitch is the rotation about the negative y axis. Roll is the rotation about the positive x axis.

So where is the negative z axis? Where is the z axis? Is it relative to the earth? Or itself?

Hi there,

It depends on your reference frame. This sandcastle example demonstrates how these reference frames relate to one another.

Thanks!
Gabby

Thanks.