# Discreet data interpolation

Hello everyone! I struggle to solve one problem. I have discreet set of data of 2 functions C_L(alpha) and C_D(alpha) - lift coefficient and drag coefficient depending on angle of attack alpha. The set looks as follows:

ALPHA_CL = [-180.0, -160.0, -90.0, -20.0, -10.0, -5.0, 0.0, 20.0, 40.0, 90.0, 160.0, 180.0]
CL_LIST = [ 0.0, 0.5, 0.0, 0.08, 0.125, 0.15, 0.2, 1.0, 1.0, 0.0, -0.5, 0.0]

ALPHA_CD = [-180.0, -170.0, -140.0, -90.0, -20.0, 0.0, 20.0, 90.0, 140.0, 170.0, 180.0]
CD_LIST = [ 0.5, 0.5, 0.5, 1.0, 0.2, 0.1, 0.2, 1.0, 0.5, 0.5, 0.5]

I need those coefficients to calculate lift and drag force acting on kite.
F_L= 0.5 * rho * pow(v,2) * C_L(alpha)

How can I interpolate these sets of data so that when I calculate alpha angle - I can precisely determine C_L and D_L coefficients.

thank You for help

I assume that you mean, that you need the interpolation between the discreet values to calculate for any value?

In this article about noise several methods to interpolate discreet values are shown, linear, cosine, cubic interpolation and smoothing. That might work for your values as well:

Thank You! that’s exactly what I needed!