iPhone EXIF data

I am using the iPhone EXIF data from a photo that I am capturing.

Currently the EXIF data I am getting back is:

{
    ApertureValue = "2.970854";
    ColorSpace = 1;
    ComponentsConfiguration =     (1,2,3,);
    ExifVersion =     (2,2,1);
    ExposureMode = 0;
    ExposureProgram = 2;
    ExposureTime = "0.03333334";
    FNumber = "2.8";
    Flash = 16;
    FlashPixVersion =     (1,0);
    FocalLength = "3.85";
    ISOSpeedRatings =     (500);
    MeteringMode = 3;
    PixelXDimension = 640;
    PixelYDimension = 480;
    SceneCaptureType = 0;
    SensingMethod = 2;
    Sharpness = 2;
    ShutterSpeedValue = "4.911055";
    SubjectArea = 开发者_如何学C    (319,239,230,172);
    WhiteBalance = 0;
}

I want to be able to add some fields such as geolocation, date and time. How can I specify new keys that I want returned? Anyone know how this is possible in ios 4.1?

I recently struggled with the same thing. See my answer to this question which shows how to do geotagging and datetime.