2sin^2σ*sin^2β+2cos^2σcos^2β
=2(1-cos^2a)(1-cos^2b)+2cos^2acos^2b
=2-2(cos^2a+cos^2b)+4cos^2acos^2b
=-cos2a-cos2b+4(cos2a+1)(cos2b+1)/4
=1+cos2σ*cos2β