Geometry 对象浅析_.Net教程

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　　说起在DataGrid中添加新行，ASP.NET开发的大牛人物：Dino Esposito，他的《构建WEB解决方案--应用ASP.NET和ADO.NET》一书中提供了和以上两位类似的方法，但是Dino又加了些功能，首先就是&rd

　　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。

　　Geometry库中几个核心类和接口构成了Geometry对象的基本框架。

　　GeometryEnvironment

　　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。

以下为引用的内容： public IPolyline TestGeometryEnvironment() { 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; spatialReferenceResolution.ConstructFromHorizon(); ISpatialReferenceTolerance spatialReferenceTolerance = spatialReferenceResolution as ISpatialReferenceTolerance; spatialReferenceTolerance.SetDefaultXYTolerance(); ISpatialReference spatialReference = spatialReferenceResolution as ISpatialReference; //Create an array of WKSPoint structures starting in the middle of the x,y domain of the //projected coordinate system. double xMin; double xMax; double yMin; double yMax; spatialReference.GetDomain(out xMin, out xMax, out yMin, out yMax); double xFactor = (xMin xMax) * 0.5; double yFactor = (yMin yMax) * 0.5; WKSPoint[] wksPoints = new WKSPoint[10]; for (int i = 0; i < wksPoints.Length; i ) { wksPoints[i].X = xFactor i; wksPoints[i].Y = yFactor i; } IPointCollection4 pointCollection = new PolylineClass(); IGeometryBridge2 geometryBridge = new GeometryEnvironmentClass(); geometryBridge.AddWKSPoints(pointCollection, ref wksPoints); IPolyline polyline = pointCollection as IPolyline; polyline.SpatialReference = spatialReference; 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）。

　　GeometryBag

　　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。

以下为引用的内容： private IPolygon GeometryBag_Example(IFeatureClass featureClass) { //Check input objects. if (featureClass == null) { return null; } IGeoDataset geoDataset = featureClass as IGeoDataset; ISpatialFilter queryFilter = new SpatialFilterClass(); //Set the properties of the spatial filter here. IGeometry geometryBag = new GeometryBagClass(); //Define the spatial reference of the bag before adding geometries to it. geometryBag.SpatialReference = geoDataset.SpatialReference; //Use a nonrecycling cursor so each returned geometry is a separate object. IFeatureCursor featureCursor = featureClass.Search(queryFilter, false); IGeometryCollection geometryCollection = geometryBag as IGeometryCollection; IFeature currentFeature = featureCursor.NextFeature(); while (currentFeature != null) { //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; 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. // 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(); unionedPolygon.ConstructUnion(geometryBag as IEnumGeometry); return unionedPolygon as IPolygon; }

　　Points

　　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。

　　Multipoints

　　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。

　　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。

以下为引用的内容： public IPolyline ConstructMultiPartPolyline(IPolyline inputPolyline) { IGeometry outGeometry = new PolylineClass(); //Always associate new, top-level geometries with an appropriate spatial reference. outGeometry.SpatialReference = inputPolyline.SpatialReference; IGeometryCollection geometryCollection = outGeometry as IGeometryCollection; ISegmentCollection segmentCollection = inputPolyline as ISegmentCollection; //Iterate over existing polyline segments using a segment enumerator. IEnumSegment segments = segmentCollection.EnumSegments; ISegment currentSegment; int partIndex = 0;; int segmentIndex = 0;; segments.Next(out currentSegment,ref partIndex, ref segmentIndex); while(currentSegment != null) { 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 //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. ISegmentCollection newPath = new PathClass(); object missing = Type.Missing; newPath.AddSegment(normal as ISegment, ref missing, ref missing); //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); } //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。

　　Polyline结构图

　　Polygons

　　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。

　　Polygon结构图

　　Multipatch

　　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。

　　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() { //Prepare the geometry material list. IGeometryMaterial texture = new GeometryMaterialClass(); texture.TextureImage = "C:\\Temp\\MyImage.bmp"; IGeometryMaterialList materialList = new GeometryMaterialListClass(); materialList.AddMaterial(texture); //Create the multipatch. IGeneralMultiPatchCreator multiPatchCreator = new GeneralMultiPatchCreatorClass(); multiPatchCreator.Init(4, 1, false, false, false, 4, materialList); //Set up part. //Could also use a Ring or a TriangleFan. multiPatchCreator.SetPatchType(0, esriPatchType.esriPatchTypeTriangleStrip); multiPatchCreator.SetMaterialIndex(0, 0); multiPatchCreator.SetPatchPointIndex(0, 0); multiPatchCreator.SetPatchTexturePointIndex(0, 0); //Set real-world points. WKSPointZ upperLeft = new WKSPointZ(); WKSPointZ lowerLeft = new WKSPointZ(); WKSPointZ upperRight = new WKSPointZ(); WKSPointZ lowerRight = new WKSPointZ(); upperLeft.X = 0; upperLeft.Y = 0; upperLeft.Z = 0; upperRight.X = 300; upperRight.Y = 0; upperRight.Z = 0; lowerLeft.X = 0; lowerLeft.Y = 0; lowerLeft.Z = -100; lowerRight.X = 300; lowerRight.Y = 1; lowerRight.Z = -100; multiPatchCreator.SetWKSPointZ(0, ref upperRight); multiPatchCreator.SetWKSPointZ(1, ref lowerRight); multiPatchCreator.SetWKSPointZ(2, ref upperLeft); multiPatchCreator.SetWKSPointZ(3, ref lowerLeft); //Set texture points. //Set the texture coordinates for a panel. WKSPoint textureUpperLeft = new WKSPoint(); WKSPoint textureLowerLeft = new WKSPoint(); WKSPoint textureUpperRight = new WKSPoint(); WKSPoint textureLowerRight = new WKSPoint(); textureUpperLeft.X = 0; textureUpperLeft.Y = 0; textureUpperRight.X = 1; textureUpperRight.Y = 0; textureLowerLeft.X = 0; textureLowerLeft.Y = 1; textureLowerRight.X = 1; textureLowerRight.Y = 1; multiPatchCreator.SetTextureWKSPoint(0, ref textureUpperRight); multiPatchCreator.SetTextureWKSPoint(1, ref textureLowerRight); multiPatchCreator.SetTextureWKSPoint(2, ref textureUpperLeft); multiPatchCreator.SetTextureWKSPoint(3, ref textureLowerLeft); IMultiPatch multiPatch = multiPatchCreator.CreateMultiPatch() as IMultiPatch; return multiPatch; }

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