How to save GPS info to an image's Properties

Question

Dear All,
I am trying to save GPS information to an image, but I 've got an error message: "The parameter is incorrect. WinRT information: Cannot write to the specified property (System.GPS.Latitude). The property is read-only."
Could you please help me to find out what's the wrong with my source code?
And is System.GPS.Latitude a read-only property? How can I change the property to read/write?
double GPSLatitude = 25.125965;
List<string> propertiesName = new List<string>();
propertiesName.Add("System.GPS.Latitude");
IDictionary<string, object> extraProperties = await photoStorageFile.Properties.RetrievePropertiesAsync(propertiesName);
extraProperties.Add("System.GPS.Latitude", GPSLatitude);
await photoStorageFile.Properties.SavePropertiesAsync(extraProperties);
Thanks,
Angie

Answer 1

I'm trying to achieve the same result, but using a BitmapEncoder.
The Latitude works fine but I just can't seem to get the Longitude to write to the file correctly.
(All the other properties are working fine.)
The inputStream is from the webcam via a capture control.
Pretty sure the decoder would behave the same if inputStream was from an StorageFile though.
Any ideas please?
Windows.Storage.Streams.IRandomAccessStream outputStream = await imageFile.OpenAsync(FileAccessMode.ReadWrite);
var decoder = await Windows.Graphics.Imaging.BitmapDecoder.CreateAsync(inputStream);
BitmapEncoder encoder = await Windows.Graphics.Imaging.BitmapEncoder.CreateForTranscodingAsync(outputStream, decoder);
BitmapPropertySet bitmapPropSet = new BitmapPropertySet();
bitmapPropSet.Add("System.Subject", new BitmapTypedValue(txtPhotoSubject.Text.Trim(), PropertyType.String));
bitmapPropSet.Add("System.GPS.LatitudeNumerator", new BitmapTypedValue(new int[3] { 47, 38, 24471 }, PropertyType.Int32Array));
bitmapPropSet.Add("System.GPS.LatitudeDenominator", new BitmapTypedValue(new int[3] { 1, 1, 1000 }, PropertyType.Int32Array));
bitmapPropSet.Add("System.GPS.LatitudeRef", new BitmapTypedValue("E", PropertyType.String));
bitmapPropSet.Add("System.GPS.LongitudeNumerator", new BitmapTypedValue(new int[3] { 122, 7, 470316 }, PropertyType.Int32Array));
bitmapPropSet.Add("System.GPS.LongitudeDenominator", new BitmapTypedValue(new int[3] { 1, 1, 10000 }, PropertyType.Int32Array));
bitmapPropSet.Add("System.GPS.LongitudeRef", new BitmapTypedValue("N", PropertyType.String));
await encoder.BitmapProperties.SetPropertiesAsync(bitmapPropSet);
await encoder.FlushAsync();
Here's the resulting properties...
EDIT (2nd Oct 2013)
Only thing that seems to fix the issue is to not include the LongitudeDenominator property.
Commenting out that line works ok.
I also needed to leave the LatitudeDenominator as 1,1,1 and just include the whole seconds.
Close enough.