SUBROUTINE SPRECT1

 SPRECT1 converts a  spherical coordinate value (in a latitude/longitude style spherical system) to  rectangular coordinates. The transformation from a latitude/longitude pair (a,b) in degrees to a rectangular (x,y) pair is:

        a = b * sgn(r) + a
        x = cos( a * pi / 180) * r / 90 + x0
        y = sin( a * pi / 180) * r / 90 + y0
where
        pi = 3.141592654

CALL SPRECT1(v,t,p,r)

v  (R): output vector containing rectangular (z,y,z) coordinates
        dimensioned v(3) (returned)
t  (R): theta (longitude) angle (rad)
p  (R): phi (latitude) angle (rad)
r  (R): radius