ArcGIS Runtime SDK for iOS開發系列教程（7）——GeometryService與GeometryEngine使用

　　在我們使用其他WebAPIs開發應用時，常常會用到GeometryService進行空間位置判斷、距離面積量測、緩沖區分析等幾何操作。在ArcGIS for Server10.1中提供的GemetryService主要包括以下操作：

　　那么，在ArcGIS for iOS中通過使用GeometryServiceTask可以很方便地使用ArcGIS的GeometryService，它所包括的操作主要有（下圖左側）：

　　同時，在ArcGIS for iOS中還封裝了本地進行幾何操作的類——GeometryEngine，極大的提高了幾何操作的效率。他所提供的操作主要如上圖的右側。下面我們將通過最簡單的緩沖區操作來向大家展示在ArcGIS for iOS中GeometryService和GeometryEngine的使用方法。

　　首先，我們構建一個支持ArcGIS的SDK的工程，在.h文件中添加GeometryServiceTask和相關協議GeometryServiceTaskDelegate，當然包括要素圖層的添加，如下圖：

　　有了上一講中Tasks使用流程的實踐，相信大家對使用協議的委托模式已經相當熟悉。接下來，我們需要對GeometryServicesTask進行初始化和實現GeometryServiceTaskDelegate的相關方法，首先在AGSMapViewTouchDelegate的地圖點擊實現方法方法中初始化GeometryServicesTask和相關參數

-(void)mapView:(AGSMapView *)mapView didClickAtPoint:(CGPoint)screen mapPoint:(AGSPoint *)mappoint graphics:(NSDictionary *)graphics
{
    NSMutableArray *geometryArray=[NSMutableArray array];
    [geometryArray addObject:mappoint];
    
    AGSPictureMarkerSymbol *pt=[AGSPictureMarkerSymbol pictureMarkerSymbolWithImageNamed:@"ArcGIS.bundle/GPSDisplay.png"];
   
    AGSGraphic *pushpin=[[AGSGraphic alloc]initWithGeometry:mappoint symbol:pt attributes:nil infoTemplateDelegate:nil];
    [_graphicsLayer addGraphic:pushpin];
    [pushpin release];
        
    [_graphicsLayer dataChanged];
    
    [_mapView centerAtPoint:mappoint animated:YES];
    
    //GeometryService
    self.gst=[[[AGSGeometryServiceTask alloc]initWithURL:[NSURL URLWithString:kGeometryBufferService]]autorelease];
    AGSSpatialReference *sr=[[[AGSSpatialReference alloc]initWithWKID:102100 WKT:nil]autorelease];
    
    self.gst.delegate=self;
    
    AGSBufferParameters *bufferParams=[[AGSBufferParameters alloc]init];
    bufferParams.unit=kesriSRUnit_Meter;
    bufferParams.bufferSpatialReference=sr;
    
    bufferParams.distances = [NSArray arrayWithObjects:
                              [NSNumber numberWithUnsignedInteger:10000],
                              [NSNumber numberWithUnsignedInteger:30000],
                              [NSNumber numberWithUnsignedInteger:50000],
                              nil];
    bufferParams.geometries = geometryArray;
    bufferParams.outSpatialReference = sr;
    bufferParams.unionResults = FALSE;
    
    [self.gst bufferWithParameters:bufferParams];
    [bufferParams release];
   
}

　　然后，添加GeometryService執行buffer操作的響應操作，成功返回處理：

-(void)geometryServiceTask:(AGSGeometryServiceTask *)geometryServiceTask operation:(NSOperation *)op didReturnBufferedGeometries:(NSArray *)bufferedGeometries
{
    UIAlertView *av = [[UIAlertView alloc] initWithTitle:@"GeometryService"
												 message:[NSString stringWithFormat:@"成功返回%d個緩沖區！", [bufferedGeometries count]]
												delegate:self
									   cancelButtonTitle:@"確定"
									   otherButtonTitles:nil];
	[av show];
	[av release];
       
    // Create a SFS for the inner buffer zone
    AGSSimpleFillSymbol *innerSymbol = [AGSSimpleFillSymbol simpleFillSymbol];
    innerSymbol.color = [[UIColor redColor] colorWithAlphaComponent:0.40];
    innerSymbol.outline.color = [UIColor darkGrayColor];
    // Create a SFS for the outer buffer zone
    AGSSimpleFillSymbol *outerSymbol = [AGSSimpleFillSymbol simpleFillSymbol];
    outerSymbol.color = [[UIColor yellowColor] colorWithAlphaComponent:0.25];
    outerSymbol.outline.color = [UIColor darkGrayColor];
    // counter to help us determine if the geometry returned is inner/outer
    
    NSUInteger i = 0;
    
    for (AGSGeometry* g	in bufferedGeometries) {
		
		// initialize the graphic for geometry
		AGSGraphic *graphic = [[AGSGraphic alloc] initWithGeometry:g symbol:nil attributes:nil infoTemplateDelegate:nil];
		
		// since we have 2 buffer distances, we know that 0-2 will be 100m buffer and 3-5 will be 300m buffer
		if (i < [bufferedGeometries count]/2) {
			graphic.symbol = innerSymbol;
		}
		else {
			graphic.symbol = outerSymbol;
		}
        
		// add graphic to the graphic layer
		[self.graphicsLayer addGraphic:graphic];
		
		// release our alloc'd graphic
		[graphic release];
		
		// increment counter so we know which index we are at
		i++;
	}
    // let the graphics layer know it has new graphics to draw
    [self.graphicsLayer dataChanged]; 
}

　　可以看出成功執行GeometryService的buffer操作后，返回結果是數組(NSArray *)bufferedGeometries，通過遍歷將Geometry轉化為要素來展示。另外，我們還需要添加出錯的處理：

- (void)geometryServiceTask:(AGSGeometryServiceTask *)geometryServiceTask operation:(NSOperation*)op didFailBufferWithError:(NSError *)error {
	UIAlertView *av = [[UIAlertView alloc] initWithTitle:@"Error"
												 message:@"There was an error with the buffer task"
												delegate:self
									   cancelButtonTitle:@"Ok"
									   otherButtonTitles:nil];
	[av show];
	[av release];
}

　　這個與其他Tasks的提示類似，不做過多解釋。這樣，我們就完成了使用GeometryServiceTask來實現緩沖區分析的操作。

　　接下來，我們來看如何通過GeometryEngine來實現同樣的操作：

-(void)mapView:(AGSMapView *)mapView didClickAtPoint:(CGPoint)screen mapPoint:(AGSPoint *)mappoint graphics:(NSDictionary *)graphics
{
    NSMutableArray *geometryArray=[NSMutableArray array];
    [geometryArray addObject:mappoint];
    
    //[_graphicsLayer removeAllGraphics];
    
    AGSPictureMarkerSymbol *pt=[AGSPictureMarkerSymbol pictureMarkerSymbolWithImageNamed:@"ArcGIS.bundle/GPSDisplay.png"];
   
    AGSGraphic *pushpin=[[AGSGraphic alloc]initWithGeometry:mappoint symbol:pt attributes:nil infoTemplateDelegate:nil];
    [_graphicsLayer addGraphic:pushpin];
    [pushpin release];
        
    [_graphicsLayer dataChanged];
    
    [_mapView centerAtPoint:mappoint animated:YES];
    //GeometryEngine
    AGSGeometryEngine *geoEng=[AGSGeometryEngine defaultGeometryEngine];
    
    // Create a SFS for the inner buffer zone
    AGSSimpleFillSymbol *innerSymbol = [AGSSimpleFillSymbol simpleFillSymbol];
    innerSymbol.color = [[UIColor redColor] colorWithAlphaComponent:0.40];
    innerSymbol.outline.color = [UIColor darkGrayColor];
    // Create a SFS for the outer buffer zone
    AGSSimpleFillSymbol *outerSymbol = [AGSSimpleFillSymbol simpleFillSymbol];
    outerSymbol.color = [[UIColor yellowColor] colorWithAlphaComponent:0.25];
    outerSymbol.outline.color = [UIColor darkGrayColor];
    
    for (int i=10; i>0;i--)
    {
        AGSPolygon *geBuffer=[geoEng bufferGeometries:geometryArray byDistance:i*1000];
        AGSGraphic *gr = [[AGSGraphic alloc] initWithGeometry:geBuffer symbol:nil attributes:nil infoTemplateDelegate:nil];
        if (i%2==1)
        {
            gr.symbol=outerSymbol;
        }
        else
        {
            gr.symbol=innerSymbol;
        }        
        
        //[self.graphicsLayer addGraphic:gr];
    }
    
    [self.graphicsLayer dataChanged];
}

　　我們不難發現，使用GeometryEngine實現同樣的buffer操作更加便捷，如果你實際操作的話，你還好發現它的效率要比GeomertyServiceTask高很多。

效果：

　　　總結：本講主要通過GeometryServiceTask和GeometryEngine的使用來向大家展示在ArcGIS for iOS中如何實現幾何相關的操作，其他具體操作，如長度計算、面積量測等大家可以參考幫助文檔。下一講將向大家介紹Geoprocessor相關的操作，歡迎大家繼續關注！