GDAL/OGR创建DXF文件中多图层的方法 .

转载自博客:http://blog.youkuaiyun.com/ivan_ljf/article/details/9177977

有人认为新建多个OGRLayer就可以将类别分开，这种观点是错误的，OGRLayer和DXF中的图层不是一个概念。

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

[cpp]  view plain copy

1. // 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  
2.     OGRFieldDefn  oLayerField( "Layer", OFTString );  
3.     poFeatureDefn->AddFieldDefn( &oLayerField );  
4.     // 好像未被使用，不管它  
5.     OGRFieldDefn  oClassField( "SubClasses", OFTString );  
6.     poFeatureDefn->AddFieldDefn( &oClassField );  
7.     // 好像未被使用，也不管它  
8.     OGRFieldDefn  oExtendedField( "ExtendedEntity", OFTString );  
9.     poFeatureDefn->AddFieldDefn( &oExtendedField );  
10.     // 线类型字段  
11.     OGRFieldDefn  oLinetypeField( "Linetype", OFTString );  
12.     poFeatureDefn->AddFieldDefn( &oLinetypeField );  
13.     // 好像未被使用，也不管它  
14.     OGRFieldDefn  oEntityHandleField( "EntityHandle", OFTString );  
15.     poFeatureDefn->AddFieldDefn( &oEntityHandleField );  
16.     //文本字段 好像未被使用，也不管它  
17.     OGRFieldDefn  oTextField( "Text", OFTString );  
18.     poFeatureDefn->AddFieldDefn( &oTextField );  
19.     // 块名称 写块时设置此字段  
20.     OGRFieldDefn  oBlockField( "BlockName", OFTString );  
21.     poFeatureDefn->AddFieldDefn( &oBlockField );  
22.     // 块缩放 写块时设置此字段  
23.     OGRFieldDefn  oScaleField( "BlockScale", OFTRealList );  
24.     poFeatureDefn->AddFieldDefn( &oScaleField );  
25.     // 块角度 写块时设置此字段  
26.     OGRFieldDefn  oBlockAngleField( "BlockAngle", OFTReal );  
27.     poFeatureDefn->AddFieldDefn( &oBlockAngleField );  

下面我们做个试验，看以下创建DXF图层的方法，代码如下：

[cpp]  view plain copy

1. #include "ogrsf_frmts.h"  
2. #include "stdio.h"  
3. #include <iostream>  
4. #include <string>  
5. using namespace std;  
6.   
7. int main()  
8. {  
9.     const char *pszDriverName = "DXF";  
10.     OGRSFDriver *poDriver;  
11.   
12.     RegisterOGRDXF();  
13.   
14.     poDriver = OGRSFDriverRegistrar::GetRegistrar()->GetDriverByName(  
15.         pszDriverName );  
16.     if( poDriver == NULL )  
17.     {  
18.         printf( "%s driver not available.\n", pszDriverName );  
19.         exit( 1 );  
20.     }  
21.   
22.     OGRDataSource *poDS;  
23.     // 模板文件名称，文件在GDAL中data下，拷贝到与cpp同目录下  
24.     char **papszOptions = (char **)CPLCalloc(sizeof(char *),3);  
25.     papszOptions[0] = "HEADER=header.dxf";  
26.     papszOptions[1] = "TRAILER=trailer.dxf";  
27.     poDS = poDriver->CreateDataSource( "out.dxf", papszOptions );//若生成的out.dxf文件正在被CAD打开着，则再次创建时会出错，创建不成功  
28.     CPLFree(papszOptions);  
29.     if( poDS == NULL )  
30.     {  
31.         printf( "Creation of output file failed.\n" );  
32.         exit( 1 );  
33.     }  
34.   
35.     OGRLayer *poLayer;  
36.   
37.     poLayer = poDS->CreateLayer( "hatch_out", NULL, wkbUnknown, NULL );  
38.     if( poLayer == NULL )  
39.     {  
40.         printf( "Layer creation failed.\n" );  
41.         exit( 1 );  
42.     }  
43.   
44.     OGRFeature *poFeature = OGRFeature::CreateFeature( poLayer->GetLayerDefn() );  
45.   
46.     // 生成一个正方形,放置在"Square"图层  
47.     OGRLinearRing oSquare;  
48.     oSquare.addPoint(0.0,0.0);  
49.     oSquare.addPoint(1.0,0.0);  
50.     oSquare.addPoint(1.0,1.0);  
51.     oSquare.addPoint(0.0,1.0);  
52.     oSquare.closeRings();  
53.     poFeature->SetField( "Layer", "Square" );  
54.     poFeature->SetGeometry( &oSquare );  
55.     if( poLayer->CreateFeature( poFeature ) != OGRERR_NONE )  
56.     {  
57.         printf( "Failed to create feature in dxffile.\n" );  
58.         exit( 1 );  
59.     }  
60.   
61.     // 生成一个三角形,放置在"三角形"图层  
62.     poFeature = OGRFeature::CreateFeature( poLayer->GetLayerDefn() );  
63.     OGRLinearRing oTriangle;  
64.     oTriangle.addPoint(2.0,2.0);  
65.     oTriangle.addPoint(3.0,2.0);  
66.     oTriangle.addPoint(3.0,3.0);  
67.     oTriangle.closeRings();  
68.     poFeature->SetField( "Layer", "Triangle" );  
69.     poFeature->SetGeometry( &oTriangle );  
70.     if( poLayer->CreateFeature( poFeature ) != OGRERR_NONE )  
71.     {  
72.         printf( "Failed to create feature in dxffile.\n" );  
73.         exit( 1 );  
74.     }  
75.   
76.     // 生成一个菱形,放置在"Triangle"图层  
77.     poFeature = OGRFeature::CreateFeature( poLayer->GetLayerDefn() );  
78.     OGRLinearRing oRhombus;  
79.     oRhombus.addPoint(4.0,3.0);  
80.     oRhombus.addPoint(5.0,4.0);  
81.     oRhombus.addPoint(4.0,5.0);  
82.     oRhombus.addPoint(3.0,4.0);  
83.     oRhombus.closeRings();  
84.     poFeature->SetField( "Layer", "Triangle" );  
85.     poFeature->SetGeometry( &oRhombus );  
86.     if( poLayer->CreateFeature( poFeature ) != OGRERR_NONE )  
87.     {  
88.         printf( "Failed to create feature in dxffile.\n" );  
89.         exit( 1 );  
90.     }  
91.   
92.     // 生成一个多段线,不设置图层，将默认层  
93.     poFeature = OGRFeature::CreateFeature( poLayer->GetLayerDefn() );  
94.     OGRLinearRing oLinearRing;  
95.     oLinearRing.addPoint(5.0,5.0);  
96.     oLinearRing.addPoint(6.0,4.0);  
97.     oLinearRing.addPoint(7.0,5.0);  
98.     oLinearRing.addPoint(8.0,4.0);  
99.     poFeature->SetGeometry( &oLinearRing );  
100.     if( poLayer->CreateFeature( poFeature ) != OGRERR_NONE )  
101.     {  
102.         printf( "Failed to create feature in dxffile.\n" );  
103.         exit( 1 );  
104.     }  
105.   
106.     OGRFeature::DestroyFeature( poFeature );  
107.   
108.     OGRDataSource::DestroyDataSource( poDS );  
109. }