The curvature of the beta-sheet in 1aps is shown by the hyperbolic paraboloid (green surface) fitted to the C-alpha atoms of the beta-sheet residues by program CURSE (Christine Mason & David S Moss, unpublished results). (Note the program is not yet widely available).
The surface was generated by CURVE, using the equation computed by CURSE, and viewed, together with the protein secondary structure, using QUANTA.