Geometry 對象淺析_.Net教程

推薦：再議ASP.NET DataGrid控件中的“添加新行”功能
　　說起在DataGrid中添加新行，ASP.NET開發的大牛人物：Dino Esposito，他的《構建WEB解決方案--應用ASP.NET和ADO.NET》一書中提供了和以上兩位類似的方法，但是Dino又加了些功能，首先就是&rd

　　ArcEngine Geometry庫定義了基本幾何圖形的矢量表達形式，頂級的幾何圖形有Points、Multipoints、Polylines、Polygons、 Multipatches，Geodatabase和繪圖系統使用這些幾何圖形來定義其他各種形狀的特征和圖形，提供了編輯圖形的操作方法和地圖符號系統符號化特征數據的途徑。

　　Geometry庫中幾個核心類和接口構成了Geometry對象的基本框架。

　　GeometryEnvironment

　　GeometryEnvironment提供了從不同的輸入、設置或獲取全局變量來創建幾何圖形的方法，以便控制geometry方法的行為。GeometryEnvironment對象是一個單例對象。

以下為引用的內容： 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僅僅是創建了一個指向已存在的GeometryEnvironmentClass的引用。注意 IGeometryBridge2接口的使用，addWKSPoints方法將WKSPoint二維點添加到PointCollection中，用于構建 path、ring、polyline、polygon，或增加新點到Multipoint、TriangleFan、TriangleStrip。在 Geometry庫中，除了IGeometryBridge2還有IGeometryBridge接口，后者繼承了前者，增加了一些編輯功能（添加點、插入點、重置點、分段等）。

　　GeometryBag

　　GeometryBag是支持IGeometry接口的幾何對象引用的集合，任何幾何對象都可以通過IGeometryCollection接口添加到 GeometryBag中，但是在使用拓撲操作的時候，需要注意不同類型的幾何類型可能會有相互不兼容的情況。在向GeometryBag中添加幾何對象的時候，GeometryBag對象需要指定空間參考，添加到其中的幾何對象均擁有和GeometryBag對象一樣的空間參考。

以下為引用的內容： 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

　　一個點包括X、Y坐標，同時可以增加M、Z值及ID屬性來擴展點的功能。

　　Multipoints

　　點的集合，多點組成Multipoint幾何類型，使用multipoint對象實現了的IPointCollection接口可以訪問所有的點元素，這些點同樣可以擁有M、Z值及ID屬性來獲得更多的地理空間內涵。

　　下面列舉一個例子，通過一個已知的polyline來定義一個新的multipart polyline。

以下為引用的內容： 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方法用來在弧段上的某一點生成該弧段的法線，指定其長度，這樣就生成了新的segment，并且多個path添加到geometryCollection中，以IPolyline的形式返回。

　　Polylines

　　Polylines是有序path組成的集合，可以擁有M、Z和ID屬性值。Polyline對象的IPointCollection接口包含了所有節點的復制，IGeometryCollection接口可以獲取polyline的paths，ISegmentCollection接口可以獲取 polyline的segments。

　　Polyline結構圖

　　Polygons

　　Polygon是一系列rings組成的集合，可以擁有M、Z和ID屬性值。每一個ring由一個或多個segment組成，Polygon或ring對象的IPointCollection接口包含了所有節點的復制，IGeometryCollection接口可以獲取polygon的rings， ISegmentCollection接口可以獲取polygon的segments。

　　Polygon結構圖

　　Multipatch

　　Multipatch用于描述3D面狀幾何類型，由一系列的矢量三角形構成，如果其中的part是一個ring，那么它必須是封閉的，第一個節點和最后一個節點相同，另外每個part所包含節點的順序非常重要，Inner Rings在Outer Rings之后，代表單個表面patch的一系列rings必須由第一個ring開始。

　　在9.0以后的開發包中，使用IGeneralMultiPatchCreator創建新的Multipatch，IGeometryMaterial進行材質貼圖。

以下為引用的內容： 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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