Affine-transform-based Newton-Raphson algorithm for videoly measuring blade deformation

Video measurement has great value in determining the deformation of helicopter blades and an efficient correlation algorithm of digital image is crucial. A Newton-Raphson algorithm method based on affine transform is proposed considering the characteristics of helicopter blade motion and deformation. First, affine transform parameters are determined by respectively selecting three match feature points in the reference image and deformed image using human-computer interaction method. Then, the initial displacements for Newton-Raphson algorithm is calculated based on the affine transform displacement mode. The global interpolation method is adopted to avoid superfluous and respective interpolation in the iteration process, which cuts down the amount of computation to 1% of that of the conventional method. The results show that the Newton-Raphson algorithm based on affine transform has much less computation expense with high accuracy and is suitable for objects with rigid body rotation.