各位大侠请教 WKB 和 AGF 的格式说明

[zhshly007]

小弟今日研究PostGis，数据以AsBinary形式提供，但格式均为WKB和AGF格式，不知哪位高人帮帮小弟，提供一下这些格式的具体说明；小弟谢谢了！

[jixingzhong]

搜索 Geometry格式转换函数

[zhshly007]

看来不用了，呵呵呵，找到了；
Well-known binary (WKB) representation
This section describes the well-known binary representation for geometries.

The OpenGIS Consortium "Simple Features for SQL" specification defines the well-known binary representation. This representation is also defined by the International Organization for Standardization (ISO) "SQL/MM Part: 3 Spatial" standard. See the related reference section at the end of this topic for information on functions that accept and produce the WKB.

The basic building block for well-known binary representations is the byte stream for a point, which consists of two double values. The byte streams for other geometries are built using the byte streams for geometries that are already defined.

The following example illustrates the basic building block for well-known binary representations.

// Basic Type definitions
// byte : 1 byte
// uint32 : 32 bit unsigned integer (4 bytes)
// double : double precision number (8 bytes)

// Building Blocks : Point, LinearRing

Point {
double x;
double y;
};
LinearRing {
uint32 numPoints;
Point points[numPoints];
};
enum wkbGeometryType {
wkbPoint = 1,
wkbLineString = 2,
wkbPolygon = 3,
wkbMultiPoint = 4,
wkbMultiLineString = 5,
wkbMultiPolygon = 6
};
enum wkbByteOrder {
wkbXDR = 0, // Big Endian
wkbNDR = 1 // Little Endian
};
WKBPoint {
byte byteOrder;
uint32 wkbType; // 1=wkbPoint
Point point;
};
WKBLineString {
byte byteOrder;
uint32 wkbType; // 2=wkbLineString
uint32 numPoints;
Point points[numPoints];
};

WKBPolygon {
byte byteOrder;
uint32 wkbType; // 3=wkbPolygon
uint32 numRings;
LinearRing rings[numRings];
};
WKBMultiPoint {
byte byteOrder;
uint32 wkbType; // 4=wkbMultipoint
uint32 num_wkbPoints;
WKBPoint WKBPoints[num_wkbPoints];
};
WKBMultiLineString {
byte byteOrder;
uint32 wkbType; // 5=wkbMultiLineString
uint32 num_wkbLineStrings;
WKBLineString WKBLineStrings[num_wkbLineStrings];
};

wkbMultiPolygon {
byte byteOrder;
uint32 wkbType; // 6=wkbMultiPolygon
uint32 num_wkbPolygons;
WKBPolygon wkbPolygons[num_wkbPolygons];
};

WKBGeometry {
union {
WKBPoint point;
WKBLineString linestring;
WKBPolygon polygon;
WKBMultiPoint mpoint;
WKBMultiLineString mlinestring;
WKBMultiPolygon mpolygon;
}
};

The following figure shows an example of a geometry in well-known binary representation using NDR coding.

Figure 58. Geometry representation in NDR format. (B=1) of type polygon (T=3) with 2 linears (NR=2), where each ring has 3 points (NP=3).