Diagram of 2-D interpolation. (a) Diagram of data transfers from Cartesian grid to curvilinear- rid. The red point is the interpolation receiving point in the polar coordinate system that receives the interpolation information from black diamonds in the Cartesian grid. (b) Diagram of data transfers from curvilinear- rid to Cartesian grid. The red point belongs to the ghost point layer in the Cartesian grid. Black diamonds that belong to the curvilinear- rid provide the information used to interpolate.