[U,V]= (pi/2:.1:3*pi/2,-pi:.2:pi); XS=cos(U)*sin(V); YS=cos(U)*cos(V); ZS=sin(U); XC=max(-2,min(2,1/(cos(U)*sin(V))))/4; YC=max(-2,min(2,1/(cos(U)*cos(V))))/4; ZC=max(-2,min(2,1/sin(U)))/4; X=XS-XC; Y=YS-YC; Z=ZS-ZC;