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[转自 Flyingis]Geometry 对象浅析

發布時間：2023/12/19 编程问答 26 豆豆

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作者：Flyingis

??? 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。

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。

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。

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。

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;
}

???
參考資料：ArcEngine 9.2幫助文檔?作者：Flyingis

??? 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。

???
參考資料：ArcEngine 9.2幫助文檔

轉載于:https://www.cnblogs.com/sueliva/archive/2010/12/07/1899019.html

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