Viewpoint planning plays an important role in automatic 3D model generation. We have proposed an optimal viewpoint planning [9] for the purpose of model generation by merging images acquired from multiple viewpoints on a sphere that encircles object. This method uses a discretized approximate sphere which involves problems of sphere tessellation and of sphere representation. One must consider that the scanned surface of an object is projected onto a sphere, and that the computational cost increases directly with the number of images. However, there are no appropriate sphere representation methods available. This paper proposes a new representation method based on a 2D array, and develops a new viewpoint planning algorithm. The proposed system is verified by algorithmic analysis and experiments using a real modeling system. © 2004 Wiley Periodicals, Inc.