iPhone iOS how to extract photo metadata and geotagging info from a camera roll image?

Question

Possible Duplicate:
How Do I Get The Correct Latitude and Longitude From An Uploaded iPhone Photo?

I'm making a photo app and would like to know what are my options for working with geotagged photos. I would like to display where a photo has been taken (similar to photos app). Is this possible?

Additionally, I need to know when the picture has been taken. I can capture this info for the pictures that I take myself, but what about the camera roll images?

Answer 1

Yes, it is possible.

You have to use ALAssetsLibrary to access your camera roll. Then you just enumerate through your photos and asks for location.

assetsLibrary = [[ALAssetsLibrary alloc] init];
groups = [NSMutableArray array];

[assetsLibrary enumerateGroupsWithTypes:ALAssetsGroupSavedPhotos  usingBlock:^(ALAssetsGroup *group, BOOL *stop)
{
    if (group == nil)
    {
        return;
    }

    [groups addObject:group];

} failureBlock:^(NSError *error)
{
    // Possibly, Location Services are disabled for your application or system-wide. You should notify user to turn Location Services on. With Location Services disabled you can't access media library for security reasons.

}];

This will enumerate your assets groups. Next, you pick up a group and enumerate its assets.

ALAssetGroup *group = [groups objectAtIndex:0];
[group enumerateAssetsUsingBlock:^(ALAsset *result, NSUInteger index, BOOL *stop)
 {
     if (result == nil)
     {
         return;
     }

     // Trying to retreive location data from image
     CLLocation *loc = [result valueForProperty:ALAssetPropertyLocation];    
 }];

Now your loc variable contains location of the place where the photo was taken. You should check it against ALErrorInvalidProperty before use, since some photos might lack this data.

You can specify ALAssetPropertyDate to obtain the date and time of photo creation.