glproj = `
float y0 = abs(y), n = ${projection.spacing()};
if (y0 > 2.) transparent = true;
x *= .5, y *= .5;
float x2 = x * x,
y2 = y * y,
ta = 2. * y / (1. + x2 + y2); // tanh(nPhi)
ta = pow((1. + ta) / (1. - ta), 1. / n);
if (x2 + y2 > 1.) transparent = true;
lambda = atan(2. * x, 1. - x2 - y2) / n;
phi = asin((ta - 1.) / (ta + 1.));
`