Closed hollow shapes based on DGM25

As closed hollow shapes are drainless sinks. With assumed water impermeability and constant irrigation, they would be with water. The determination of hollow shapes is a relatively simple geomorphographic evaluation of digital terrain models. For automatic determination, an algorithm by Wang & Liu (2006) is used at the core. Manual verification and correction is recommended, since the automatically determined closed hollow forms can also be of anthropogenic origin (e.g. small quarries or clay pits) and so-called half-dolins are not closed hollow shapes and are therefore not recorded. Wang, L. & Liu, H. (2006): An Efficient Method for Identifying and Filling Surface Depressions in Digital Elevation Models for Hydrologic Analysis and Modelling. International Journal of Geographical Information Science, 20, 193-213. http://dx.doi.org/10.1080/13658810500433453