A simple data transformation technique for pre-processing survey data at embayed beaches

This note explains a technique used for pre-processing three-dimensional survey data obtained at embayed beaches that exhibit distinct alongshore curvature. Using a log-spiral function fitted to the beach planform, the data is transformed from Cartesian into an alternative alongshore–cross-shore coordinate system. When undergoing this transformation, the curvature in the survey data is effectively removed. This greatly simplifies the application of standard interpolation methods, and in this transformed coordinate system the alongshore and cross-shore directions are now explicitly defined. Using a property unique to the log-spiral, the interpolated data is readily transformed back into the original Cartesian coordinate system for further analyses and interpretation. The practical application and advantages of this technique are then demonstrated using survey data from two embayed beaches in south-eastern Australia.