Z_CUT_RATIO
float dz = sqrt(1.0 - (DH_REF*DH_REF + DV_REF*DV_REF) * (0.5 + 0.5/Z_CUT_RATIO) * (0.5 + 0.5/Z_CUT_RATIO));
fDepthRef = dz / (1.0 - 1.0/Z_CUT_RATIO);
fGeometry.z_min = fDepthRef/Z_CUT_RATIO;
if (i&4) p1 = p1 * (1.0 / Z_CUT_RATIO);