A second - order fast marching eikonal solver

Unfortunately, first-order implementations lead to inaccuracies in computed traveltimes, which may lead to poor image focusing for migration applications. In addition, first-order traveltimes are not accurate enough for reliable amplitude calculations. This has lead to the development of the fast marching method on non-Cartesian (Alkhalifah and Fomel, 1997; Sun and Fomel, 1998), and even unstructured (Fomel, 1997) grids. These non-Cartesian formulations reduce inaccuracies, while retaining the fast marching method’s characteristic stability and efficiency. Unfortunately, the cost is the loss of algorithmic simplicity.