This figure shows the two-dimensional faces of two abutting unstructured grid cells. The donor cell face is a triangle, drawn using solid lines, and is labeled as "TRI_3 face element #1893". Its corners are labeled "node 1", "node 2", and "node 3". The receiving cell face is a quadrilateral, drawn using dashed lines, with one corner labeled "R" inside the donor cell face. Arrows are drawn showing that the location of point "R" in the donor zone is "0.34 in the 1-2 direction" and "0.61 in the 1-3 direction".