Geometry 对象浅析
ArcEngine Geometry库定义了基本几何图形的矢量表达形式，顶级的几何图形有Points、Multipoints、Polylines、Polygons、 Multipatches，Geodatabase和绘图系统使用这些几何图形来定义其他各种形状的特征和图形，提供了编辑图形的操作方法和地图符号系统符号化特征数据的途径。 CHINAZ
Geometry库中几个核心类和接口构成了Geometry对象的基本框架。 CHINAZ
GeometryEnvironment CHINAZ
GeometryEnvironment提供了从不同的输入、设置或获取全局变量来创建几何图形的方法，以便控制geometry方法的行为。GeometryEnvironment对象是一个单例对象。
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以下为引用的内容： public IPolyline TestGeometryEnvironment() { CHINAZ  ISpatialReferenceFactory spatialReferenceFactory = new SpatialReferenceEnvironmentClass(); //Create a projected coordinate system and define its domain, resolution, and x,y tolerance. ISpatialReferenceResolution spatialReferenceResolution = spatialReferenceFactory.CreateProjectedCoordinateSystem((int)esriSRProjCSType.esriSRProjCS_NAD1983UTM_11N) as ISpatialReferenceResolution; CHINAZ spatialReferenceResolution.ConstructFromHorizon(); ISpatialReferenceTolerance spatialReferenceTolerance = spatialReferenceResolution as ISpatialReferenceTolerance; spatialReferenceTolerance.SetDefaultXYTolerance(); ISpatialReference spatialReference = spatialReferenceResolution as ISpatialReference;
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//Create an array of WKSPoint structures starting in the middle of the x,y domain of the //projected coordinate system. double xMin; double xMax;
CHINAZ double yMin; double yMax; spatialReference.GetDomain(out xMin, out xMax, out yMin, out yMax); double xFactor = (xMin + xMax) * 0.5; CHINAZ double yFactor = (yMin + yMax) * 0.5; WKSPoint[] wksPoints = new WKSPoint[10]; for (int i = 0; i < wksPoints.Length; i++) CHINAZ  { CHINAZ wksPoints[i].X = xFactor + i; wksPoints[i].Y = yFactor + i; } IPointCollection4 pointCollection = new PolylineClass();
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IGeometryBridge2 geometryBridge = new GeometryEnvironmentClass(); geometryBridge.AddWKSPoints(pointCollection, ref wksPoints); IPolyline polyline = pointCollection as IPolyline; polyline.SpatialReference = spatialReference; CHINAZ return polyline; } |
new GeometryEnvironmentClass仅仅是创建了一个指向已存在的GeometryEnvironmentClass的引用。注意 IGeometryBridge2接口的使用，addWKSPoints方法将WKSPoint二维点添加到PointCollection中，用于构建 path、ring、polyline、polygon，或增加新点到Multipoint、TriangleFan、TriangleStrip。在 Geometry库中，除了IGeometryBridge2还有IGeometryBridge接口，后者继承了前者，增加了一些编辑功能（添加点、插入点、重置点、分段等）。 CHINAZ
GeometryBag CHINAZ
GeometryBag是支持IGeometry接口的几何对象引用的集合，任何几何对象都可以通过IGeometryCollection接口添加到 GeometryBag中，但是在使用拓扑操作的时候，需要注意不同类型的几何类型可能会有相互不兼容的情况。在向GeometryBag中添加几何对象的时候，GeometryBag对象需要指定空间参考，添加到其中的几何对象均拥有和GeometryBag对象一样的空间参考。
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| 以下为引用的内容：private IPolygon GeometryBag_Example(IFeatureClass featureClass){
CHINAZ //Check input objects. if (featureClass == null) {
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return null; } IGeoDataset geoDataset = featureClass as IGeoDataset; ISpatialFilter queryFilter = new SpatialFilterClass();
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//Set the properties of the spatial filter here. IGeometry geometryBag = new GeometryBagClass(); //Define the spatial reference of the bag before adding geometries to it.
CHINAZ geometryBag.SpatialReference = geoDataset.SpatialReference; //Use a nonrecycling cursor so each returned geometry is a separate object. IFeatureCursor featureCursor = featureClass.Search(queryFilter, false);
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IGeometryCollection geometryCollection = geometryBag as IGeometryCollection; IFeature currentFeature = featureCursor.NextFeature(); while (currentFeature != null) CHINAZ { CHINAZ //Add a reference to this feature's geometry into the bag. //You don't specify the before or after geometry (missing), //so the currentFeature.Shape IGeometry is added to the end of the geometryCollection. object missing = Type.Missing; CHINAZ geometryCollection.AddGeometry(currentFeature.Shape, ref missing, ref missing); currentFeature = featureCursor.NextFeature(); } // Create the polygon that will be the union of the features returned from the search cursor. CHINAZ // The spatial reference of this feature does not need to be set ahead of time. The // ConstructUnion method defines the constructed polygon's spatial reference to be the same as // the input geometry bag. ITopologicalOperator unionedPolygon = new PolygonClass();
CHINAZ unionedPolygon.ConstructUnion(geometryBag as IEnumGeometry); return unionedPolygon as IPolygon;} |
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Points
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一个点包括X、Y坐标，同时可以增加M、Z值及ID属性来扩展点的功能。 CHINAZ
Multipoints CHINAZ
点的集合，多点组成Multipoint几何类型，使用multipoint对象实现了的IPointCollection接口可以访问所有的点元素，这些点同样可以拥有M、Z值及ID属性来获得更多的地理空间内涵。
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下面列举一个例子，通过一个已知的polyline来定义一个新的multipart polyline。
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| 以下为引用的内容：public IPolyline ConstructMultiPartPolyline(IPolyline inputPolyline){
CHINAZ IGeometry outGeometry = new PolylineClass(); //Always associate new, top-level geometries with an appropriate spatial reference. outGeometry.SpatialReference = inputPolyline.SpatialReference;
CHINAZ IGeometryCollection geometryCollection = outGeometry as IGeometryCollection; ISegmentCollection segmentCollection = inputPolyline as ISegmentCollection; //Iterate over existing polyline segments using a segment enumerator. CHINAZ IEnumSegment segments = segmentCollection.EnumSegments; ISegment currentSegment; int partIndex = 0;; int segmentIndex = 0;;
CHINAZ segments.Next(out currentSegment,ref partIndex, ref segmentIndex); while(currentSegment != null) {
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ILine normal = new LineClass(); //Geometry methods with _Query_ in their name expect to modify existing geometries. //In this case, the QueryNormal method modifies an existing line //segment (normal) to be the normal vector to
CHINAZ //currentSegment at the specified location along currentSegment. currentSegment.QueryNormal(esriSegmentExtension.esriNoExtension, 0.5, true, currentSegment.Length / 3, normal); //Since each normal vector is not connected to others, create a new path for each one. CHINAZ ISegmentCollection newPath = new PathClass(); object missing = Type.Missing; newPath.AddSegment(normal as ISegment, ref missing, ref missing); CHINAZ //The spatial reference associated with geometryCollection will be assigned to all incoming paths and segments. geometryCollection.AddGeometry(newPath as IGeometry, ref missing, ref missing); segments.Next(out currentSegment,ref partIndex, ref segmentIndex); CHINAZ } //The geometryCollection now contains the new, multipart polyline. return geometryCollection as IPolyline;} |
ISegment接口的QueryNormal方法用来在弧段上的某一点生成该弧段的法线，指定其长度，这样就生成了新的segment，并且多个path添加到geometryCollection中，以IPolyline的形式返回。
Polylines
Polylines是有序path组成的集合，可以拥有M、Z和ID属性值。Polyline对象的IPointCollection接口包含了所有节点的复制，IGeometryCollection接口可以获取polyline的paths，ISegmentCollection接口可以获取 polyline的segments。 CHINAZ
Polyline结构图 CHINAZ
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Polygons CHINAZ
Polygon是一系列rings组成的集合，可以拥有M、Z和ID属性值。每一个ring由一个或多个segment组成，Polygon或ring对象的IPointCollection接口包含了所有节点的复制，IGeometryCollection接口可以获取polygon的rings， ISegmentCollection接口可以获取polygon的segments。 CHINAZ
Polygon结构图
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Multipatch CHINAZ
Multipatch用于描述3D面状几何类型，由一系列的矢量三角形构成，如果其中的part是一个ring，那么它必须是封闭的，第一个节点和最后一个节点相同，另外每个part所包含节点的顺序非常重要，Inner Rings在Outer Rings之后，代表单个表面patch的一系列rings必须由第一个ring开始。
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在9.0以后的开发包中，使用IGeneralMultiPatchCreator创建新的Multipatch，IGeometryMaterial进行材质贴图。
| 以下为引用的内容：public IMultiPatch CreateMultipatch(){
CHINAZ //Prepare the geometry material list. IGeometryMaterial texture = new GeometryMaterialClass(); texture.TextureImage = "C:\\Temp\\MyImage.bmp";
CHINAZ IGeometryMaterialList materialList = new GeometryMaterialListClass(); materialList.AddMaterial(texture); //Create the multipatch. IGeneralMultiPatchCreator multiPatchCreator = new GeneralMultiPatchCreatorClass();
CHINAZ multiPatchCreator.Init(4, 1, false, false, false, 4, materialList); //Set up part. //Could also use a Ring or a TriangleFan.
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multiPatchCreator.SetPatchType(0, esriPatchType.esriPatchTypeTriangleStrip); multiPatchCreator.SetMaterialIndex(0, 0); multiPatchCreator.SetPatchPointIndex(0, 0); multiPatchCreator.SetPatchTexturePointIndex(0, 0);
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//Set real-world points. WKSPointZ upperLeft = new WKSPointZ(); WKSPointZ lowerLeft = new WKSPointZ(); WKSPointZ upperRight = new WKSPointZ();
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WKSPointZ lowerRight = new WKSPointZ(); upperLeft.X = 0; upperLeft.Y = 0; upperLeft.Z = 0;
CHINAZ upperRight.X = 300; upperRight.Y = 0; upperRight.Z = 0; lowerLeft.X = 0;
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lowerLeft.Y = 0; lowerLeft.Z = -100; lowerRight.X = 300; lowerRight.Y = 1;
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lowerRight.Z = -100; multiPatchCreator.SetWKSPointZ(0, ref upperRight); multiPatchCreator.SetWKSPointZ(1, ref lowerRight); multiPatchCreator.SetWKSPointZ(2, ref upperLeft); CHINAZ multiPatchCreator.SetWKSPointZ(3, ref lowerLeft); //Set texture points. //Set the texture coordinates for a panel. WKSPoint textureUpperLeft = new WKSPoint();
CHINAZ WKSPoint textureLowerLeft = new WKSPoint(); WKSPoint textureUpperRight = new WKSPoint(); WKSPoint textureLowerRight = new WKSPoint(); textureUpperLeft.X = 0; CHINAZ textureUpperLeft.Y = 0; textureUpperRight.X = 1; textureUpperRight.Y = 0; textureLowerLeft.X = 0; CHINAZ textureLowerLeft.Y = 1; textureLowerRight.X = 1; textureLowerRight.Y = 1; multiPatchCreator.SetTextureWKSPoint(0, ref textureUpperRight); CHINAZ multiPatchCreator.SetTextureWKSPoint(1, ref textureLowerRight); multiPatchCreator.SetTextureWKSPoint(2, ref textureUpperLeft); multiPatchCreator.SetTextureWKSPoint(3, ref textureLowerLeft); IMultiPatch multiPatch = multiPatchCreator.CreateMultiPatch() as IMultiPatch; CHINAZ return multiPatch;} |
