Coordinate Structure

The coordinate description of an object may consist of several parts. The first part is called the object description, and the remaining parts are subobject descriptions. The purpose of subobjects depends on the localization type.

For areal objects, subobjects describe internal boundaries. For example: a clearing in a forest, islands in a swamp, and so on. It is not recommended to use subobjects to describe a group of areal objects.

For linear objects, subobjects describe the continuation of objects after forced breaks in the representation. For example: a road passing through a river or under another road may be interrupted by a bridge, tunnel, overpass, etc.

For labels, subobjects may describe the placement of individual text lines and individual template components (lines, point symbols). The template content depends on the classification code (characteristics of forest vegetation, bridges, overpasses, etc., have different templates described in the digital classifier).

The number of subobjects is specified in a record of the following format:

.MET number_of_subobjects

The number of subobjects is an integer from 0 to 65536.

If the number of subobjects is zero, this record may be omitted.

The list of object coordinates begins with a record containing the number of points (a positive integer). This is followed by records of point coordinates. The coordinates of one point are placed on a single line.

Point coordinates may appear as:

x y H

for a rectangular coordinate system, or

B L H

for geodetic coordinates.

The type of coordinate system and other information is contained in the passport data section. If the passport data section is not filled, the coordinates are assumed to be in a rectangular local system.

Rectangular coordinates are always specified in meters (floating-point representation is possible).

Geodetic coordinates are always specified in radians.

Height is always specified in meters (e.g.: -5, 15.75, 8.173E6) and may be indicated for all objects, for specific objects, or omitted entirely.

The number of coordinate records must equal the number of object points.

For objects of the label type (TIT), the coordinates of the object and subobjects must be followed by label text in the following format:

>LABEL TEXT

If there is no record with label text (> ...) when describing the geometry of the object or subobjects, then this geometry describes auxiliary elements of the label template (lines, point symbols, etc.), the specific content of which is determined by the object's classification code.

After the description of the object's coordinates comes the description of the subobject's coordinates, if the number of subobjects is not zero. Otherwise, what follows is the description of the object's semantics (attributes) (.SEM), or the description of the next object (.OBJ), or the end of the data set (.END).