Executing spatial queries

空间查询是基于与某几何要素的空间关系的查询。

1.Finding features within a polygon

// Get the feature and its geometry given an ObjectID.IFeature stateFeature = stateFeatureClass.GetFeature(14);IGeometry queryGeometry = stateFeature.ShapeCopy;// Create the spatial filter; "highwayFeatureClass" is the feature class containing// the highway data. Set the SubFields property to "FULL_NAME" as only that field// is shown.ISpatialFilter spatialFilter = new SpatialFilterClass();spatialFilter.Geometry = queryGeometry;spatialFilter.GeometryField = highwayFeatureClass.ShapeFieldName;spatialFilter.SpatialRel = esriSpatialRelEnum.esriSpatialRelIntersects;spatialFilter.SubFields = "FULL_NAME";// Find the position of the "FULL_NAME" field in the highway feature class.int nameFieldPosition = highwayFeatureClass.FindField("FULL_NAME");// Execute the query and iterate through the cursor's results.using(ComReleaser comReleaser = new ComReleaser()){    IFeatureCursor highwayCursor = highwayFeatureClass.Search(spatialFilter, false);    comReleaser.ManageLifetime(highwayCursor);    IFeature highwayFeature = null;    while ((highwayFeature = highwayCursor.NextFeature()) != null)    {        String name = Convert.ToString(highwayFeature.get_Value(nameFieldPosition));        Console.WriteLine("Highway found: {0}", name);    }}

2.Querying for features with relation to multiple geometries

这个场景展示了如何使用geometry bag进行几何查询。geometry bag是一个单一的高层次的几何形状，存储的几何形状的集合。下列代码演示了如何在一组已知的block features中找到geometry bag。block features不相邻，但其ObjectIds是已知的。

// Create a geometry bag and give it the same spatial reference as the// blocks feature class.IGeometryBag geometryBag = new GeometryBagClass();IGeometryCollection geometryCollection = (IGeometryCollection)geometryBag;IGeoDataset geoDataset = (IGeoDataset)blocksFeatureClass;ISpatialReference spatialReference = geoDataset.SpatialReference;geometryBag.SpatialReference = spatialReference;// Get a feature cursor for the three blocks and put their geometries into the geometry bag.// A non-recycling cursor is used, as the features' geometries are stored// for later use.int[] blockObjectIDs = {    11043, 11049, 11057};using(ComReleaser comReleaser = new ComReleaser()){    IFeatureCursor blocksCursor = blocksFeatureClass.GetFeatures(blockObjectIDs,        false);    comReleaser.ManageLifetime(blocksCursor);    IFeature blockFeature = null;    object missingType = Type.Missing;    while ((blockFeature = blocksCursor.NextFeature()) != null)    {        geometryCollection.AddGeometry(blockFeature.Shape, ref missingType, ref            missingType);    }}

When using a geometry bag as the query geometry, create a spatial index on the geometry bag to allow rapid access to the contained geometries during the spatial query. See the following code example:

// Cast the geometry bag to the ISpatialIndex interface and call the Invalidate method// to generate a new spatial index.ISpatialIndex spatialIndex = (ISpatialIndex)geometryBag;spatialIndex.AllowIndexing = true;spatialIndex.Invalidate();

现在的geometry bag可以用作一个新的空间滤波器的几何查询。下面的代码示例演示如何使用“包含”（包含在块中的完全的空间关系）的空间过滤器，以找到三个区块内的包裹数量：

// Create the spatial filter. The SubFields property specifies that only// the Shape field is retrieved, since the features' attributes aren't being inspected.ISpatialFilter spatialFilter = new SpatialFilterClass();spatialFilter.Geometry = geometryBag;spatialFilter.GeometryField = parcelsFeatureClass.ShapeFieldName;spatialFilter.SpatialRel = esriSpatialRelEnum.esriSpatialRelContains;spatialFilter.SubFields = "Shape";// Use IFeatureClass.FeatureCount to get a parcel count.int parcelCount = parcelsFeatureClass.FeatureCount(spatialFilter);Console.WriteLine("Parcels in the three blocks: {0}", parcelCount);

3.Buffering and querying

// Find the feature for Osaka and get its geometry.IFeature osakaFeature = citiesFeatureClass.GetFeature(2263);IGeometry osakaGeometry = osakaFeature.ShapeCopy;// Use the ITopologicalOperator interface to create a buffer.ITopologicalOperator topoOperator = (ITopologicalOperator)osakaGeometry;IGeometry buffer = topoOperator.Buffer(500000);

4.Evaluating a specific spatial relationship using IRelationalOperator

// Get the marsh and highway features from their respective classes.IFeature marshFeature = vegFeatureClass.GetFeature(518);IFeature highwayFeature = roadsFeatureClass.GetFeature(39);// Get the geometries of the two features.IGeometry marshGeometry = marshFeature.Shape;IGeometry highwayGeometry = highwayFeature.Shape;// Cast the highway's geometry to IRelationalOperator and determine if// it crosses the marsh's geometry.IRelationalOperator relationalOperator = (IRelationalOperator)highwayGeometry;Boolean crosses = relationalOperator.Crosses(marshGeometry);Console.WriteLine("Highway crosses marsh: {0}", crosses);