PURPOSE:To speedily calculate the r.theta interpolation coefficient in a short time with a high-speed. CONSTITUTION:Sin gamma/ D, cosgamma/ D, cosalpha, sinalpha, cosbeta, sinbeta are read out from a table memory 1 by inputting a number N of a line segment on which a sampling point is and a sampling point distance D on the same line segment. With these and the input of (x-x0) and (y-y0), a=(x-x0)cosalpha-(y-y0)sinalpha, b=-(x-x0) cosbeta+(y-y0)sinbeta are obtained by multipliers 4 to 7 and adders 9 and 10. The a/(a+b) and b/(a+b) are read out from a table memory 11. The {(x-x0)singamma+(y- y0)cosgamma} D is calculated by multipliers 2 and 3 and an adder 8. Introducing below the decimal points of this value by a below-decimal-point extraction circuit 12, r1/r1+r2 is obtained as well as r2/(r1+r2) is obtained by an adder 13. The interpolation coefficient is calculated from r1/(r1+r2), r2/(r1+r2), a/(a+b), and b/(a+b) by multipliers 14 to 17.
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