struct PK_UVBOX_s
    {
    double param[4];
    };
typedef struct PK_UVBOX_s PK_UVBOX_t;



This structure represents a rectangular region of a surface's parameter space.


Specific Errors:
    PK_ERROR_bad_uvbox              not a valid region of a surface's parameter
                                    space.


The doubles in a PK_UVBOX_t are in the following order:

    param[0] low  U value
    param[1] low  V value
    param[2] high U value
    param[3] high V value

`param[0]' must be less than or equal to `param[2]'.
If these two values are equal, the uvbox has a zero extent in the U direction.
`param[1]' must be less than or equal to `param[3]'.
If these two values are equal, the uvbox has a zero extent in the V direction.

The low U and V values both lie inside the surface's parameter range as given
by PK_SURF_ask_uvbox. For a non-periodic parameter, the high value also lies in
that range.  For a periodic parameter, the high value will lie in the period
above the low value if the required uvbox crosses the seam.

The only exception to the above occurs when a face lies partly on the extension
of its surface, in which case the uvbox returned by PK_FACE_find_uvbox will
contain parameters outside the base range of the surface.