Default SIP order from 2 to 3?

[han-k59]

The default setting for SIP order is 2. Assuming the distortion can be modeled by typical barrel or pincushion distortion an order of 3 gives much better accuracy. Practical tests prove this.

So I would suggest to set the default SIP order at 3. Mathematically this is also easy to prove. See below.

Han

Standard distortion modelling:

{Xdelta:=Xideal*(k1*r1^2 + k2*r1^4 + ....)

simplify by taking only the first factor

Xdelta:=Xideal* k1*r1^2 

Xdelta:=Xideal* k1*(X^2+Y^2)

Xdelta:=k1*X^3+  k1* X*Y^2           X^3 is factor AP_3_0      and X*Y^2   is factor AP_1_2