图层设置GDAL/OGR创建DXF文件中多图层的方法

最近使用开发的过程中出现了一个小问题，顺便记录一下原因和方法--图层设置

    在使用GDAL/OGR创立DXF，偶然会将点、线、面数据分到到各自的图层中，或者同类别的要素、对象写到DXF文件中不同的图层。如下图：

    

    有人认为新建多个OGRLayer就能够将类别离开，这种观念是错误的，OGRLayer和DXF中的图层不是一个概念。

    在写DXF文件时，不支持创立多个ORGLayer图层，一个OGRDXFWriterDS对应一个OGRDXFWriterLayer在new OGRDXFWriterLayer时，OGRDXFWriterLayer构造函数中，会创立DXF标准字段也就是OGRFieldDefn，DXF不支持额定的新建字段：标准字段新建代码（在OGRDXFWriterLayer.cpp中第58-83行）：

// 图层字段，设置此字段，将要素分类到，所设置的图层中，不设置默认为0层
	OGRFieldDefn  oLayerField( "Layer", OFTString );
    poFeatureDefn->AddFieldDefn( &oLayerField );
	// 似乎未被使用，不管它
    OGRFieldDefn  oClassField( "SubClasses", OFTString );
    poFeatureDefn->AddFieldDefn( &oClassField );
	// 似乎未被使用，也不管它
    OGRFieldDefn  oExtendedField( "ExtendedEntity", OFTString );
    poFeatureDefn->AddFieldDefn( &oExtendedField );
	// 线类型字段
    OGRFieldDefn  oLinetypeField( "Linetype", OFTString );
    poFeatureDefn->AddFieldDefn( &oLinetypeField );
	// 似乎未被使用，也不管它
    OGRFieldDefn  oEntityHandleField( "EntityHandle", OFTString );
    poFeatureDefn->AddFieldDefn( &oEntityHandleField );
	//文本字段 似乎未被使用，也不管它
    OGRFieldDefn  oTextField( "Text", OFTString );
    poFeatureDefn->AddFieldDefn( &oTextField );
	// 块名称 写块时设置此字段
    OGRFieldDefn  oBlockField( "BlockName", OFTString );
    poFeatureDefn->AddFieldDefn( &oBlockField );
    // 块缩放 写块时设置此字段
    OGRFieldDefn  oScaleField( "BlockScale", OFTRealList );
    poFeatureDefn->AddFieldDefn( &oScaleField );
    // 块角度 写块时设置此字段
    OGRFieldDefn  oBlockAngleField( "BlockAngle", OFTReal );
    poFeatureDefn->AddFieldDefn( &oBlockAngleField );

    
 

    上面我们做个试验，看以下创立DXF图层的方法，代码如下：

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#include "ogrsf_frmts.h"
#include "stdio.h"
#include <iostream>
#include <string>
using namespace std;

int main()
{
	const char *pszDriverName = "DXF";
	OGRSFDriver *poDriver;

	RegisterOGRDXF();

	poDriver = OGRSFDriverRegistrar::GetRegistrar()->GetDriverByName(
		pszDriverName );
	if( poDriver == NULL )
	{
		printf( "%s driver not available.\n", pszDriverName );
		exit( 1 );
	}

	OGRDataSource *poDS;
	// 模板文件名称，文件在GDAL中data下，拷贝到与cpp同目录下
	// 也可以设置GDAL_DATA路径
	// 按下设置，也可以设置一个正确的相对路径和绝对路径
	char **papszOptions = (char **)CPLCalloc(sizeof(char *),3);
	papszOptions[0] = "HEADER=header.dxf";
	papszOptions[1] = "TRAILER=trailer.dxf";
	poDS = poDriver->CreateDataSource( "out.dxf", papszOptions );
	CPLFree(papszOptions);
	if( poDS == NULL )
	{
		printf( "Creation of output file failed.\n" );
		exit( 1 );
	}

	OGRLayer *poLayer;

	poLayer = poDS->CreateLayer( "hatch_out", NULL, wkbUnknown, NULL );
	if( poLayer == NULL )
	{
		printf( "Layer creation failed.\n" );
		exit( 1 );
	}

	OGRFeature *poFeature = OGRFeature::CreateFeature( poLayer->GetLayerDefn() );

	// 生成一个正方形,放置在"正方形"图层
	OGRLinearRing oSquare;
	oSquare.addPoint(0.0,0.0);
	oSquare.addPoint(1.0,0.0);
	oSquare.addPoint(1.0,1.0);
	oSquare.addPoint(0.0,1.0);
	oSquare.closeRings();
	poFeature->SetField( "Layer", "正方形" );
	poFeature->SetGeometry( &oSquare );
	if( poLayer->CreateFeature( poFeature ) != OGRERR_NONE )
	{
		printf( "Failed to create feature in shapefile.\n" );
		exit( 1 );
	}

	// 生成一个三角形,放置在"三角形"图层
	poFeature = OGRFeature::CreateFeature( poLayer->GetLayerDefn() );
	OGRLinearRing oTriangle;
	oTriangle.addPoint(2.0,2.0);
	oTriangle.addPoint(3.0,2.0);
	oTriangle.addPoint(3.0,3.0);
	oTriangle.closeRings();
	poFeature->SetField( "Layer", "三角形" );
	poFeature->SetGeometry( &oTriangle );
	if( poLayer->CreateFeature( poFeature ) != OGRERR_NONE )
	{
		printf( "Failed to create feature in shapefile.\n" );
		exit( 1 );
	}

	// 生成一个菱形,放置在"三角形"图层
	poFeature = OGRFeature::CreateFeature( poLayer->GetLayerDefn() );
	OGRLinearRing oRhombus;
	oRhombus.addPoint(4.0,3.0);
	oRhombus.addPoint(5.0,4.0);
	oRhombus.addPoint(4.0,5.0);
	oRhombus.addPoint(3.0,4.0);
	oRhombus.closeRings();
	poFeature->SetField( "Layer", "三角形" );
	poFeature->SetGeometry( &oRhombus );
	if( poLayer->CreateFeature( poFeature ) != OGRERR_NONE )
	{
		printf( "Failed to create feature in shapefile.\n" );
		exit( 1 );
	}

	// 生成一个多段线,不设置图层，将默认层
	poFeature = OGRFeature::CreateFeature( poLayer->GetLayerDefn() );
	OGRLinearRing oLinearRing;
	oLinearRing.addPoint(5.0,5.0);
	oLinearRing.addPoint(6.0,4.0);
	oLinearRing.addPoint(7.0,5.0);
	oLinearRing.addPoint(8.0,4.0);
	poFeature->SetGeometry( &oLinearRing );
	if( poLayer->CreateFeature( poFeature ) != OGRERR_NONE )
	{
		printf( "Failed to create feature in shapefile.\n" );
		exit( 1 );
	}

	OGRFeature::DestroyFeature( poFeature );

	OGRDataSource::DestroyDataSource( poDS );
}

    

文章结束给大家分享下程序员的一些笑话语录： 古鸽是一种搜索隐禽，在中国快绝迹了…初步的研究表明，古鸽的离去，很可能导致另一种长着熊爪，酷似古鸽，却又习性不同的猛禽类——犤毒鸟

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图层和设置
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