Height estimation methods for filling gaps in gridded DTM

Digital terrain models (DTMs) describing the relief of the terrain constitute a central component of mapping and geographic information systems, in general, and photogrammetric mapping, in particular. In practice, the limitations of photogrammetric measurement methods for collecting the relief information cause discontinuities and gaps in the database. The possibility of automatically completing and correcting the missing information by calculation, without requiring additional measuring, offers an inexpensive, rapid, and attractive alternative. This paper presents an analysis based on practical experiments of the capabilities and limitations of various methods of filling the gaps in gridded relief databases. Also presented are effects of different relief types and grids of varying densities on the accuracy obtained in automatically filling the gaps in gridded DTM databases. The recommended estimation method is based on a weighted average of 1D third-order polynomials assembled around the required point in two prime directions. The proposed method is much faster than other common methods such as 2D polynomials, kriging, etc., yet it is just as accurate. This method can therefore be employed in the course of using various applications, in real time, with no need for editing and preliminary changes of the relief data in the database.