Seconds in exif gps values for ios mobile pics are always null

[Dyloneus]

I've run into a problem where exif gps info from ios devices. The [seconds] rational (from ExifTag.GPSLongitude array) is always 0.

It works ok with android and other images. Here's what i'm trying to do:

`internal static ExifGPSCoordinates GetGPSCoordinates(IExifProfile exifProfile)
{
ExifGPSCoordinates gpsCoordinates = null;
var gpsLongitude = exifProfile.GetValue(ExifTag.GPSLongitude);
var gpsLongitudeRef = exifProfile.GetValue(ExifTag.GPSLongitudeRef);
var gpsLatitude = exifProfile.GetValue(ExifTag.GPSLatitude);
var gpsLatitudeRef = exifProfile.GetValue(ExifTag.GPSLatitudeRef);

        if ((gpsLongitudeRef != null && gpsLongitude != null) &&
            (gpsLatitudeRef != null && gpsLatitude != null))
        {
            gpsCoordinates = new ExifGPSCoordinates
            {
                Longitude = (decimal)GetCoordinates(gpsLongitudeRef.ToString(), gpsLongitude.Value),
                Latitude = (decimal)GetCoordinates(gpsLatitudeRef.ToString(), gpsLatitude.Value)
            };
        }

        return gpsCoordinates;
    }

    private static double? GetCoordinates(string gpsRef, Rational[] rationals)
    {
        if (string.IsNullOrEmpty(gpsRef) && (rationals == null || rationals.Length == 0))
        {
            return null;
        }

        double degrees = rationals[0].Numerator / rationals[0].Denominator;
        double minutes = rationals[1].Numerator / rationals[1].Denominator;
        double seconds = rationals[2].Numerator / rationals[2].Denominator;

        double coordinate = degrees + (minutes / 60d) + (seconds / 3600d);
        if (gpsRef == "S" || gpsRef == "W")
            coordinate *= -1;
        return coordinate;
    }

`

Ive attached a sample ios image for testing.

You can check the metadata on https://www.pic2map.com/ which shows the coordinates to be 45° 30' 42.30" N , 122° 39' 56.38" W.

However, in the code above, the value in the [seconds] rational is 0.

Is this a bug or should I be parsing GPSLongitude and GPSLatitude out differently?

Thanks in advance for your help

[dlemstra]

Just noticed that you are doing the conversion to double yourself. You probably want to do rational.ToDouble() instead. This is unrelated to your question.

[dlemstra]

I got the correct result with the following calucation:

var value = profile.GetValue(ExifTag.GPSLongitude);

var degrees = value.Value[0].ToDouble();
var minutes = value.Value[1].ToDouble();
var seconds = value.Value[2].ToDouble();
minutes += 60 * (degrees - Math.Floor(degrees));
degrees = Math.Floor(degrees);
seconds += 60 * (minutes - Math.Floor(minutes));
minutes = Math.Floor(minutes);
var pos = $"{degrees} {minutes} {seconds}";

Did not check how to do negative values based on the LatitudeRef

[Dyloneus]

The 3rd value in the array (seconds) is always zero (Numerator = 0, Denominator = 1) when using the ios image attached to the original post.

It's populated for non-ios images (such as the one attached to this post)

The issue appears to be the exifProfile.GetValue() method which returns partial data for the rationals used to calculate gps coordinates.

Ive stumbled upon this interesting post on the difference between signed and unsigned rationals and the ios stance on the subject. Just wondering if this has anything to do with this issue?

Thanks again

[dlemstra]

The seconds are indeed zero in the image but that is not a problem. That is an allowed value and how it is stored in the image.

[Dyloneus]

If you download both images and check the gps exif data ( either using https://www.pic2map.com/ or just checking the file properties), you will see that seconds IS populated, but magick.net does not (or can not) extract it for the ios image.

That's the problem. Seconds is always zero for ios images.

[dlemstra]

Seconds is not populated, it is calculated. As you can see in my example earlier this is done:

seconds += 60 * (minutes - Math.Floor(minutes));

And that is why you see a seconds value on that site.

[Dyloneus]

Thanks Dirk,

My understanding of how this was calculated was wrong.

Works perfectly!

Much appreciated.