Geometry 对象浅析

2022-07-15 80酷酷网 80kuku.com

　　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;

}