This 'sphere' is created by calculating column capacity with generated reinforcement for all sets of axial force and bending moments. This is done by calculating equilibrium of forces in the cross section meaning that the neural axis is found (unless the entire column is under tension or compression) and then forces in each reinforcement bar as well as in concrete is determined. This is the same as for simple bending (you calculate force in compressed part of the concrete and force in reinforcement. Knowing the limit of stresses in concrete and steel you can determine the maximal bending moment the RC element can withstand) but in 3D. The formulas are these from the picture you inserted. The limits of axial force and bending moments is determined by maximal allowable stress level in concrete and steel.
I'm sorry but this would be to much of calculations
Please check this document:
This is about the simple bending (so for the column that would allow you to calculate two points of the 'sphere'; one for Mx = max and N=0 and the other for My = max and N=0 ) but the same principle applies for bi- directional bending and bi-directional bending with axial force.
We also hope that RSA will include, more features for this kind of topics , we see some power- point presentation on AU university where the speaker show a patner ship between RSA and Alstiscad about this topic, so we hope that for the next release that RSA team will include a more complete design report for design of RC shear wall in Seismic Area for major Seismic code, such as EC8, ACI and CSA etc..
as the Bentley did it recently for RAM or SOFTEK with is S-concrete modulus, as illustrated in the adress below :