GIS开源库shapeLib的使用方法（一）

    近期研究了一下GIS开源库shapeLib读写ArcGIS数据的API函数，先整理一下，将各个API的用法介绍一下。

分为两个模块，shape API和DBF API，前者的读取.shp文件的空间几何信息，后者读取.dbf文件的属性信息。

Shape API：

Shape Types （shape类型）

shape文件的类型定义如下：

#define SHPT_NULL             0

  2D Shape Types (pre ArcView 3.x):

  #define SHPT_POINT		1	Points
  #define SHPT_ARC		3	Arcs (Polylines, possible in parts)
  #define SHPT_POLYGON		5	Polygons (possible in parts)
  #define SHPT_MULTIPOINT	8	MultiPoint (related points)

  3D Shape Types (may include "measure" values for vertices):

  #define SHPT_POINTZ		11	
  #define SHPT_ARCZ		13
  #define SHPT_POLYGONZ		15
  #define SHPT_MULTIPOINTZ 	18

  2D + Measure Types:

  #define SHPT_POINTM		21
  #define SHPT_ARCM		23
  #define SHPT_POLYGONM		25
  #define SHPT_MULTIPOINTM 	28

  Complex (TIN-like) with Z, and Measure:

  #define SHPT_MULTIPATCH 	31

SHPObject  （shape文件中包含的要素对象）

typedef struct
  {
    int		nSHPType;	//Shape Type (SHPT_* - see list above) 要素类型

    int		nShapeId; 	//Shape Number (-1 is unknown/unassigned) ID

    int		nParts;		//# of Parts (0 implies single part with no info) 要素有几个部分组成
    int		*panPartStart;  //Start Vertex of part 要素部分的起始点
    int		*panPartType;	//Part Type (SHPP_RING if not SHPT_MULTIPATCH) 各个部分的类型
    
    int		nVertices;	//Vertex list 
    double	*padfX;		
    double	*padfY;
    double	*padfZ;		//(all zero if not provided)
    double	*padfM;		//(all zero if not provided)

    double	dfXMin;		//Bounds in X, Y, Z and M dimensions
    double	dfYMin;
    double	dfZMin;
    double	dfMMin;

    double	dfXMax;
    double	dfYMax;
    double	dfZMax;
    double	dfMMax;
  } SHPObject;

SHPOpen()  

SHPHandle SHPOpen( const char * pszShapeFile, const char * pszAccess );

  pszShapeFile:		//shape文件的全路径

  pszAccess:		//打开方式 "rb" (read-only binary) and "rb+" (read/write binary) 		        

//打开shape文件，操作完必须调用后面的关闭。

SHPGetInfo()   //得到shape对象的信息

void SHPGetInfo( SHPHandle hSHP, int * pnEntities, int * pnShapeType,
                 double * padfMinBound, double * padfMaxBound );

  hSHP:			// shape文件的句柄 The handle previously returned by SHPOpen() 
			or SHPCreate().

  pnEntities:		A pointer to an integer into which the number of
			entities/structures should be placed.  May be NULL.

  pnShapetype:		A pointer to an integer into which the shapetype
			of this file should be placed.  Shapefiles may contain
			either SHPT_POINT, SHPT_ARC, SHPT_POLYGON or 
			SHPT_MULTIPOINT entities.  This may be NULL.

  padfMinBound:		The X, Y, Z and M minimum values will be placed into
                        this four entry array.  This may be NULL.
			
  padfMaxBound:		The X, Y, Z and M maximum values will be placed into
                        this four entry array.  This may be NULL.

SHPReadObject()  //读取每条记录中的信息

SHPObject *SHPReadObject( SHPHandle hSHP, int iShape );

  hSHP:			The handle previously returned by SHPOpen() 
			or SHPCreate().

  iShape:		The entity number of the shape to read.  Entity 
			numbers are between 0 and nEntities-1 (as returned
			by SHPGetInfo()).

SHPClose()

void	SHPClose( SHPHandle hSHP );

SHPCreate()  //创建一个shape文件

SHPHandle SHPCreate( const char * pszShapeFile, int nShapeType );

  pszShapeFile:		//创建文件的名称

  nShapeType:		//类型，参加上面定义的类型

SHPCreateSimpleObject()   //创建简单要素对象，一般调用此方法

SHPObject * 
     SHPCreateSimpleObject( int nSHPType, int nVertices, 
			    double *padfX, double * padfY, double *padfZ, );

  nSHPType:		The SHPT_ type of the object to be created, such
                        as SHPT_POINT, or SHPT_POLYGON.
  
  nVertices:		The number of vertices being passed in padfX,    
                        padfY, and padfZ. 

  padfX:		An array of nVertices X coordinates of the vertices
                        for this object.

  padfY:		An array of nVertices Y coordinates of the vertices
                        for this object.

  padfZ:		An array of nVertices Z coordinates of the vertices
                        for this object.  This may be NULL in which case
		        they are all assumed to be zero.

SHPCreateObject()  //创建复杂对象，参数中包含所有信息

SHPObject * 
     SHPCreateObject( int nSHPType, int iShape,
                      int nParts, int * panPartStart, int * panPartType,
                      int nVertices, double *padfX, double * padfY, 
                      double *padfZ, double *padfM );

  nSHPType:		The SHPT_ type of the object to be created, such
                        as SHPT_POINT, or SHPT_POLYGON.

  iShape:		The shapeid to be recorded with this shape.

  nParts:		The number of parts for this object.  If this is
                        zero for ARC, or POLYGON type objects, a single 
                        zero valued part will be created internally.
  
  panPartStart:		The list of zero based start vertices for the rings
                        (parts) in this object.  The first should always be
                        zero.  This may be NULL if nParts is 0.
  
  panPartType:		The type of each of the parts.  This is only meaningful
                        for MULTIPATCH files.  For all other cases this may
                        be NULL, and will be assumed to be SHPP_RING.
  
  nVertices:		The number of vertices being passed in padfX,    
                        padfY, and padfZ. 

  padfX:		An array of nVertices X coordinates of the vertices
                        for this object.

  padfY:		An array of nVertices Y coordinates of the vertices
                        for this object.

  padfZ:		An array of nVertices Z coordinates of the vertices
                        for this object.  This may be NULL in which case
		        they are all assumed to be zero.

  padfM:		An array of nVertices M (measure values) of the 
			vertices for this object.  This may be NULL in which 
			case they are all assumed to be zero.

SHPComputeExtents()  //重新计算记录的取值范围

void SHPComputeExtents( SHPObject * psObject );

  psObject:		An existing shape object to be updated in place.

SHPWriteObject()  //向shape文件中添加一条记录，只有先添加了记录，才能添加属性信息

int SHPWriteObject( SHPHandle hSHP, int iShape, SHPObject *psObject );

  hSHP:			The handle previously returned by SHPOpen("r+") 
			or SHPCreate().

  iShape:		The entity number of the shape to write.  A value of
		        -1 should be used for new shapes.  

  psObject:		The shape to write to the file. This should have
                        been created with SHPCreateObject(), or 
                        SHPCreateSimpleObject().

SHPDestroyObject()  //删除对象

void SHPDestroyObject( SHPObject *psObject );

  psObject:		The object to deallocate.

SHPRewindObject()

int SHPRewindObject( SHPHandle hSHP, SHPObject *psObject );

  hSHP:                 The shapefile (not used at this time).
  psObject:		The object to deallocate.

This function will reverse any rings necessary in order to enforce the shapefile restrictions on the required order of inner and outer rings in the Shapefile specification. It returns TRUE if a change is made and FALSE if no change is made. Only polygon objects will be affected though any object may be passed.