void survis (which) D3PLT.C Level 3
 
char *which = "top"        Only the top of the surface is visible.
= "bottom"   Only the bottom of the surface is visible.
= "both"       Both sides of the surface will be visible.
 
survis() can be used with surfun() and surmat(). By default, both sides of a 3-D surface will be made visible.