Matrix of depths building

Building a matrix of depths is carried out by sea maps with the classifier s57navy.rsc. Source data - one or several sheets of sea maps in format SIT or SITX. The resulting matrix contains negative depths in the sea area or a sign of depth absence (pseudo-code) in the land area.

 If the source data - several sheets of sea maps, then before the process of creating the matrix, the uniting of the source sheets is performed. The purpose of the uniting is the elimination of objects superposition of the source sea maps of different scales. On the temporary map in the areas of superposition there are objects with a more detailed source sea map (of a larger scale).

 The following objects are transferred to the temporary united map from the source sheets for constructing the depth matrix: isobath (key DEPCNT_L in the classifier s57navy.rsc), depth mark (key SOUNDG_P), land area (LNDARE_S), island (LNDARE_P), sunk ship (WRECKS_P1), obstacle (OBSTRN_S1), underwater drying rock (UWTROC_P).

 Further by objects of the temporary map a creating a matrix of depths is carried out. Building a matrix includes the following steps:

- filling the matrix with isobaths and land areas;

- filling the matrix with depth marks;

- calculation of unfilled elements by interpolation;

- filling the matrix with obstacles.

 When processing isobaths, semantics with code 174 is used (ISOBATE VALUE). To get depth, semantics 174 is used with the opposite sign. The depth value is entered into the matrix elements along which the isobath metric passes.

 When processing areas of a land into matrix elements the special sign is entered, the presence of which cancels calculation of elements values by an interpolation method. In the elements of the built matrix appropriate to the areas of a land or islands, values of depths are absent.

 To enhance the influence of a point object, the «island» of the LAND layer a special sign is put not into one element of a matrix, but into a square area from four elements. The square area contains one element of hit of the metrics point and three elements of the extension, the position of which depends on position of a point of the metrics inside the hit element. Extension elements surround the angle of the hit element closest to the metrics point.

 When processing depth marks, the depth value is selected from the third coordinate of the metric (H).  The sign of the selected value does not change, that is, the value of the third coordinate of the metric must be negative. To enhance the influence of depth marks, it is recommended to set the mode Additional processing of altitude marks = Build rays from altitude marks.

 When processing objects of the OBSTACLE layer (sunken ship, danger, underwater drying rock), semantics with code 179 (DEPTH VALUE) is used. To get depth, semantics 179 is used with the opposite sign. To enhance the influence of a point object of the OBSTACLE layer (a sunken ship, an underwater drying rock), the depth is put not into one element of a matrix, but into a square area from four elements. The square area contains one element of hit of the metrics point and three elements of the extension, the position of which depends on position of a point of the metrics inside the hit element. Extension elements surround the angle of the hit element closest to the metrics point.