The arrays and should have the same length. Each additional frame is defined by rotating frame_a around the axial vector an angle and then translating along the reference axis by . The reference axis is the next local axis after the e_axis (e.g., if e_axis is y, the reference axis is z). Figure 1 illustrates this process.
Figure 1: The axial unit vector (e_axis) for this disk is [0,1,0]. Additional frame was added by defining and . Both of these frames lie on the plane defined by the normal vector of e_axis and passing through the center of mass.
Disk mass is calculated as
where the disk material density, ρ, can be defined using the "Select density" parameter. This parameter lets the user either enter a value or select among predefined material densities.
Figure 2: Different options for the "Select density" parameter
Assuming the default direction of for the e_axis, the moments of inertia expressed from the center of mass frame (frame_a) are
The right-hand side of these equations will interchange if another axial unit vector is specified.