If numerical diffusion needs to be strongly minimised, Lagrangian and Eulerian–Lagrangian advection algorithms can be used. In geomodelling, for example, very accurate advection of non-diffusive properties such as rock type(composition) with strongly discontinuous distribution in space is often required. One of the most popular methods in this case is to combine the use of Lagrangian advecting points (markers, tracers or particles) with an immobile, Eulerian grid In this approach, properties are initially distributed on a large amount of Lagrangian points that are advected according to a given/computed velocity field. The advected material properties (e.g. density) are then interpolated from the displaced Lagrangian points to the Eulerian grid (Fig. 8.7) by using a weighteddistance averaging such as the following linear interpolation formula