Spatial description of objects

In the geo database ArcSDE, the spatial description of objects is stored in its internal format St_Geometry. This format is not a standard and the manufacturer (ESRI) can change its structure at its own discretion. In this regard, reading and recording spatial data by external clients is carried out not directly in the format St_Geometry (ArcSDE), but through conversion to the format Well-Known Binary (WKB).

The spatial data representation format WKB is defined by the standard Open Geospatial Consortium – OGC 06-103r4: «OpenGIS® Implementation Standard for Geographic information – Simple feature access – Part 1: Common architecture».

Binary representation of a geometric object (WKB) in format NDR (B = 1)

type Polygon (T = 3)

with 2 LinearRings (NR = 2)

each LinearRings consists of 3 points (NP = 3)

WKB-representation is the description of a geometric object as a set of bytes in a specific format. Such set consists of the header part and byte arrays, which determine the coordinates for the contours of the object.

The sequence of bytes can be represented using one of two standard binary encodings. The difference between the two encodings of geometry is that the sequence of bytes is encoded by the reverse order of the bytes (Big Endian) in XDR and by the direct order of bytes (Little Endian) in NDR.

To reduce computational costs, the program uses WKB with a direct order of bytes – NDR.

Geometry is supported with 2 (2D), 3 (Z and M) and 4 (ZM) – dimensional metric for the following localizations of objects are specified in the table below.

*feature «M» is not processed