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        用AGSImageServiceIdentifyTask可以获取ArcGISImageServiceLayer图层中的栅格值。这涉及了三个比较重要的类：AGSImageServiceIdentifyParameters、AGSImageServiceIdentifyTask和AGSImageServiceIdentifyResult，还有一个delegate代理类。下面一一简介一下：

AGSImageServiceIdentifyParameters

AGSImageServiceIdentifyParameters是用来设置identify参数的，可以用类方法imageServiceIdentifyParameters构造，即

[AGSImageServiceIdentifyParameters AGSImageServiceIdentifyParameters];

AGSImageServiceIdentifyParameters共包括下面几个属性

---geometry用于指定查询栅格的位置，常常是一个AGSPoint，也可以用AGSPolygon来查询一个区域的栅格值。

---mosaicRule是镶嵌规则，默认为AGSMosaicMethodCenter。

---pixelSizeX和pixelSizeY用来设置象元大小，默认为被查询栅格图层的象元大小。在象元大小范围内的所有镶嵌数据集都会被查询到。

AGSImageServiceIdentifyTask

实例化的时候需要设置查询的URL，如果需要验证的话需要设置credential

其他的没什么可介绍的，在查询的之前已经要为查询设置代理，查询的时候用- (NSOperation*) identifyWithParameters:(AGSImageServiceIdentifyParameters *)      identifyParams方法。

AGSImageServiceIdentifyResult

catelogItems是返回的栅格目录（我也不知道怎么翻译啦，一个Raster Catelog是Raster Dataset栅格数据集的集合）。

catalogItemVisibilities顾名思义，栅格目录是否可见

location就是identify的查询位置

name就是identify查询的属性名称

objectId不解释了，就是一个id

properties是一个属性的集合

value就是name对应属性的象元值

AGSImageServiceIdentifyDelegate

代理是用来获得查询结果用的，必须实现下面两个方法，第一个是identify查询失败的时候调用的，第二个是identify查询成功调用的，会获得一个AGSImageServiceIdentifyResult对象。

(void)     - imageServiceIdentifyTask:operation:didFailToIdentifyWithError:

(void)     - imageServiceIdentifyTask:operation:didIdentifyWithResult:

下面是具体的使用方法。

1、为ViewController设置代理，并实现查询完成的两个方法:

在ViewController.h中

#import <UIKit/UIKit.h>

#define IMAGE_SERVICE "http://sampleserver3.arcgisonline.com/ArcGIS/rest/services/World/MODIS/ImageServer"</p>

@interface ViewController : UIViewController <AGSImageServiceIdentifyDelegate>

@property (strong, nonatomic) AGSImageServiceIdentifyTask *task;

@end

- (void)imageServiceIdentifyTask:(AGSImageServiceIdentifyTask*)identifyTask operation:(NSOperation*)op didIdentifyWithResult:(AGSImageServiceIdentifyResult *)result{
    NSLog(@"properties :%@", result.properties);
    NSLog(@"value :%@", result.value);
    NSLog(@"name : %@", result.name);
    NSLog(@"catalogItems count :%d", [[result.catalogItems features] count]);
}

- (void)imageServiceIdentifyTask:(AGSImageServiceIdentifyTask*)identifyTask operation:(NSOperation*)op didFailToIdentifyWithError:(NSError *)error{
    NSLog(@"fault");
}

2、设置AGSImageServiceIdentifyTask:

    self.task = [[AGSImageServiceIdentifyTask alloc] initWithURL:[NSURL URLWithString:IMAGE_SERVICE]];
    self.task.delegate = self;

3、设置AGSImageServiceIdentifyParameters:

    
    AGSImageServiceIdentifyParameters *param = [AGSImageServiceIdentifyParameters imageServiceIdentifyParameters];
    
    param.geometry = [AGSPoint pointWithX:116.425541 y:39.969147 spatialReference:[AGSSpatialReference spatialReferenceWithWKID:4326]];
    
    [self.task identifyWithParameters:param];

完整的代码如下：

ViewController.h中

//  ViewController.h
//  Wang
//
//  Created by dongyu on 14-7-10.
//  Copyright (c) 2014年 org.reach. All rights reserved.
//

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController <AGSImageServiceIdentifyDelegate>

@property (strong, nonatomic) AGSImageServiceIdentifyTask *task;

@end

//  ViewController.m
//  Wang
//
//  Created by dongyu on 14-7-10.
//  Copyright (c) 2014年 org.reach. All rights reserved.
//

#import "ViewController.h"
#define IMAGE_SERVICE @"http://sampleserver3.arcgisonline.com/ArcGIS/rest/services/World/MODIS/ImageServer"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
    
    self.task = [[AGSImageServiceIdentifyTask alloc] initWithURL:[NSURL URLWithString:IMAGE_SERVICE]];
    self.task.delegate = self;
    
    AGSImageServiceIdentifyParameters *param = [AGSImageServiceIdentifyParameters imageServiceIdentifyParameters];
    
    param.geometry = [AGSPoint pointWithX:116.425541 y:39.969147 spatialReference:[AGSSpatialReference spatialReferenceWithWKID:4326]];
    
    [self.task identifyWithParameters:param];
    
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

#pragma mark - delegate
- (void)imageServiceIdentifyTask:(AGSImageServiceIdentifyTask*)identifyTask operation:(NSOperation*)op didIdentifyWithResult:(AGSImageServiceIdentifyResult *)result{
    NSLog(@"properties :%@", result.properties);
    NSLog(@"value :%@", result.value);
    NSLog(@"name : %@", result.name);
    NSLog(@"catalogItems count :%d", [[result.catalogItems features] count]);
}

- (void)imageServiceIdentifyTask:(AGSImageServiceIdentifyTask*)identifyTask operation:(NSOperation*)op didFailToIdentifyWithError:(NSError *)error{
    NSLog(@"fault");
}

@end

demo的下载地址：

http://download.csdn.net/detail/dongyu1009/7623695

新手发博文，有不好的地方，望大家批评指正。