Curvature of Model

[mrafiei]

Hi, I processed my aerial photos which captured by sony Nex-6 and I have a curved model. My area is not curved but my model is. My flight parameters are:
f=24 mm
forward overlap: 80%
side overlap: 60%
flight height: 120 m

Does every one has a solution for this? 

[bigben]

Calibrate your lens parameters and fix them