2D Modeling of structures illustrate pitfalls in imaging structures.  GX2 licensed by GX Technology is an easy to use 2D modeling program which is able to show how salt structures as shown below, defocus CDP's.  Normal CDP processing of gathers in these environments lead to eroneous amplitudes of seismic horizons as well as poor imaging because the reflection points for different source-receiver pairs from a single CDP gather are not located at a common reflection point.