在 iOS4.1 上保存带有照片的地理标记信息

问题描述

我在尝试使用 iOS4.1 上的地理标签信息将照片保存到相机胶卷时遇到重大问题.我正在使用以下 ALAssetsLibrary API:

I am having major issues trying to save a photo to camera roll with geotag info on iOS4.1. I am using following ALAssetsLibrary API:

- (void)writeImageDataToSavedPhotosAlbum:(NSData *)imageData 
                                metadata:(NSDictionary *)metadata 
                         completionBlock:(ALAssetsLibraryWriteImageCompletionBlock)completionBlock

我有 GPS 坐标，我希望将照片保存为输入.不幸的是，没有文档或示例代码描述如何形成封装 GPS 坐标的元数据 NSDictionary.有人可以发布一个已知有效的示例代码吗?

I have the GPS coordinates that i wish to save with the photo as an input. Unfortunately, there is no documentation or sample code that describes how to form the metadata NSDictionary that encapsulates the GPS coordinates. Can somebody post a sample code that is known to work ?

我也尝试过使用 iPhone Exif 库将地理信息保存在 imageData 中，而不是使用元数据，但不幸的是 iPhone Exif 库正在崩溃.非常感谢任何帮助.

I have also tried using iPhone Exif library to save geo info in imageData rather than using metadata, but unfortunately iPhone Exif library is crashing. Any help is greatly appreciated.

推荐答案

以下代码将所有可用信息从 CLLocation 对象复制到 GPS 元数据字典的正确格式:

Here is code to copy all available information from a CLLocation object into the proper format for a GPS metadata dictionary:

- (NSDictionary *)getGPSDictionaryForLocation:(CLLocation *)location {
    NSMutableDictionary *gps = [NSMutableDictionary dictionary];

    // GPS tag version
    [gps setObject:@"2.2.0.0" forKey:(NSString *)kCGImagePropertyGPSVersion];

    // Time and date must be provided as strings, not as an NSDate object
    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
    [formatter setDateFormat:@"HH:mm:ss.SSSSSS"];
    [formatter setTimeZone:[NSTimeZone timeZoneWithAbbreviation:@"UTC"]];
    [gps setObject:[formatter stringFromDate:location.timestamp] forKey:(NSString *)kCGImagePropertyGPSTimeStamp];
    [formatter setDateFormat:@"yyyy:MM:dd"];
    [gps setObject:[formatter stringFromDate:location.timestamp] forKey:(NSString *)kCGImagePropertyGPSDateStamp];
    [formatter release];

    // Latitude
    CGFloat latitude = location.coordinate.latitude;
    if (latitude < 0) {
        latitude = -latitude;
        [gps setObject:@"S" forKey:(NSString *)kCGImagePropertyGPSLatitudeRef];
    } else {
        [gps setObject:@"N" forKey:(NSString *)kCGImagePropertyGPSLatitudeRef];
    }
    [gps setObject:[NSNumber numberWithFloat:latitude] forKey:(NSString *)kCGImagePropertyGPSLatitude];

    // Longitude
    CGFloat longitude = location.coordinate.longitude;
    if (longitude < 0) {
        longitude = -longitude;
        [gps setObject:@"W" forKey:(NSString *)kCGImagePropertyGPSLongitudeRef];
    } else {
        [gps setObject:@"E" forKey:(NSString *)kCGImagePropertyGPSLongitudeRef];
    }
    [gps setObject:[NSNumber numberWithFloat:longitude] forKey:(NSString *)kCGImagePropertyGPSLongitude];

    // Altitude
    CGFloat altitude = location.altitude;
    if (!isnan(altitude)){
        if (altitude < 0) {
            altitude = -altitude;
            [gps setObject:@"1" forKey:(NSString *)kCGImagePropertyGPSAltitudeRef];
        } else {
            [gps setObject:@"0" forKey:(NSString *)kCGImagePropertyGPSAltitudeRef];
        }
        [gps setObject:[NSNumber numberWithFloat:altitude] forKey:(NSString *)kCGImagePropertyGPSAltitude];
    }

    // Speed, must be converted from m/s to km/h
    if (location.speed >= 0){
        [gps setObject:@"K" forKey:(NSString *)kCGImagePropertyGPSSpeedRef];
        [gps setObject:[NSNumber numberWithFloat:location.speed*3.6] forKey:(NSString *)kCGImagePropertyGPSSpeed];
    }

    // Heading
    if (location.course >= 0){
        [gps setObject:@"T" forKey:(NSString *)kCGImagePropertyGPSTrackRef];
        [gps setObject:[NSNumber numberWithFloat:location.course] forKey:(NSString *)kCGImagePropertyGPSTrack];
    }

    return gps;
}

将此方法返回的字典指定为您传递给 writeImageDataToSavedPhotosAlbum:metadata:completionBlock: 或 CGImageDestinationAddImage().

Assign the dictionary returned by this method as the value for the kCGImagePropertyGPSDictionary key in the metadata dictionary you pass to writeImageDataToSavedPhotosAlbum:metadata:completionBlock: or CGImageDestinationAddImage().

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