In this standard the data model of matrix structure is intended to describe the arranged set of the heights representing the relief in the framework of the digital terrain model.
Its fundamental element is the grid cell, the sides of which are parallel with the x and y axes of coordinate, their length is uniformly determined. The height of the terrain is to give with reference to the SW corner of the grid cell in the database.
The group of the grid cells arranged in matrix form makes up sub-block, which consist of n columns numbered proceeding from W to E along the y axis, along the x axis, however, it consists of m rows numbered proceeding from S to N. The heights of the grid cells forming the sub-block are arranged according to this in matrices in the database. For the identification of the matrix of height the index number of the sub-block and the identifier of the block are used.
The group of the sub-blocks arranged in matrix form makes up block, which along the y axis consist of N columns numbered proceeding from W to E, along the axis x, however, consists of M rows numbered proceeding from S to N. The index number of a certain sub-block is to count on the base of the analogy of the sequence 1, 2, ..., N, N+1, ..., 2N, 2N+1, ..., N*M.
The measure of each sub-block belonging to a certain block, number of the by sub-block grid cells and their length of side are uniform.
Block is chosen for an area unit circumscribed from a certain practical point of view, which is usually not parallelepiped, but the block has to be that. The parts forming with the difference of both are to "fill up" with sub-blocks of empty set (NULLA field) and grid cells.