.TH SFOCAL
 6 "IRIT Version 6.0" 
.SH NAME
SFOCAL



 SurfaceType SFOCAL( SurfaceType Srf, NumericType Dir )

Evaluates the focal surface field of surface Srf using the normal
curvature in the isoparametric direction as given by Dir (either
ROW or COL). Note this function is not using the principal curvatures as
is generaly the case for focal surfaces.

Example:

    gcross = cbspline( 3,
                       list( ctlpt( E3, 0.3, 0.0, 0.0 ),
                             ctlpt( E3, 0.1, 0.0, 0.1 ),
                             ctlpt( E3, 0.1, 0.0, 0.4 ),
                             ctlpt( E3, 0.5, 0.0, 0.5 ),
                             ctlpt( E3, 0.6, 0.0, 0.8 ) ),
                       list( KV_OPEN ) );
    glass = surfprev( gcross );
    color( glass, red );
    
    gfocal = SFOCAL(glass, col);

Evaluates the focal surface using the COL isoparametric direction's
normal curvature of the glass surface.