1. A method of using a multisided patch generator to generate a free-form surface by inputting data on boundary curves and spanning a multisided patch as a surface interpolating said boundary curves, said method comprising the steps of: forming a multisided coordinate system defined by m variables bi (i=1,. .. , m) for an m-sided shape and storing said m variables bi in a table; generating local parameters ui and vi from said m variables bi for each side ei of said m-sided shape and storing said local parameters ui and vi in said table; calculating curve formulas Ci, Ci+1 and Ci-1 corresponding to the side ei and the adjoining sides ei+1 and ei-1 using said local parameters, said calculating performed by a multisided patch generating processor; generating sweep surfaces Si,i+1 and Si,i-1 with said Ci as a guide curve and with Ci+1 and Ci-1 as cross-sectional curves, said generating performed by said multisided patch generating processor; interpolating said two sweep surfaces Si,i+1 and Si,i-1 sharing said guide curve using a blending function g(ui) and a blending function h(ui) to generate a blend surface Qu(ui, vi), said interpolating performed by said multisided patch generating processor; and combining said blend surfaces Qi to generate a multisided patch, said combining performed by said multisided patch generating processor.