plgvpw: Get viewport limits in world coordinates 

DESCRIPTION:

    Get viewport limits in world coordinates. 

SYNOPSIS:

plgvpw(p_xmin, p_xmax, p_ymin, p_ymax)

ARGUMENTS:

    p_xmin (PLFLT *, output) :      Lower viewport limit of the world
    coordinate in x. 

    p_xmax (PLFLT *, output) :      Upper viewport limit of the world
    coordinate in x. 

    p_ymin (PLFLT *, output) :      Lower viewport limit of the world
    coordinate in y. 

    p_ymax (PLFLT *, output) :      Upper viewport limit of the world
    coordinate in y.