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; CHINAZ
//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(); CHINAZ
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) { CHINAZ
return null; } IGeoDataset geoDataset = featureClass as IGeoDataset; ISpatialFilter queryFilter = new SpatialFilterClass(); CHINAZ
//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); CHINAZ
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) { CHINAZ
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. CHINAZ
multiPatchCreator.SetPatchType(0, esriPatchType.esriPatchTypeTriangleStrip); multiPatchCreator.SetMaterialIndex(0, 0); multiPatchCreator.SetPatchPointIndex(0, 0); multiPatchCreator.SetPatchTexturePointIndex(0, 0); CHINAZ
//Set real-world points. WKSPointZ upperLeft = new WKSPointZ(); WKSPointZ lowerLeft = new WKSPointZ(); WKSPointZ upperRight = new WKSPointZ(); CHINAZ
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; CHINAZ
lowerLeft.Y = 0; lowerLeft.Z = -100; lowerRight.X = 300; lowerRight.Y = 1; CHINAZ
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; } |