Sphere Mapping GLSL

Hello,

Could someone please tell me why ozone3d is adding 1.0 to z value for?

m = sqrt( r.x^2 * + r.y ^2 + (r.z + 1.0)^2 )

Also why would we need to add 0.5 to st coordinate?

here is the link to formula:

http://www.ozone3d.net/tutorials/glsl_texturing_p04.php#part_41

Thanks,

[Edited by - home3d2001 on September 13, 2010 12:48:41 AM]