Abstract: Sphere fitting is one of the complex and waiting prompt solution problems in the
field of 3D Converse Modeling, which can be used for the parts detection, the recovery of the
architecture, medicine and so on. The paper offers a method to directly fit sphere, called DF
algorithm, and acquire the geometric parameters with improvement at speed and accuracy. The
paper also pays attention to data analysis for the cause of the results and the comparison with the
LM (Levenberg-Marquardt) algorithm, which is the one of the most widely used nonlinear least
square methods, laying foundations for the rebuilding the parts and the gives of the further work.

Key words: direct fitting, sphere, 3D converse modeling