objective c - How to set GPano metadata of UIImages on iOS? -

i trying set metadata of uiimage spherical parameters. there multiple tutorials on web not set gpano fields.

here code using:

- (nsdata*)writemetadataintoimagedata:(nsdata*)imagedata metadata:(nsmutabledictionary*)metadataasmutable {    nsmutabledictionary *resultmutable = [metadataasmutable mutablecopy];   // create imagesourceref   cgimagesourceref source = cgimagesourcecreatewithdata((__bridge cfdataref) imagedata, null);    // read , log pre write metadata   nsdictionary* metadata = (nsdictionary *) cfbridgingrelease(cgimagesourcecopypropertiesatindex(source,0,null));   nslog(@"before:\n------------------------------%@\n------------------------------", metadata);    nsmutabledictionary* exifd = [resultmutable[(nsstring*)kcgimagepropertyexifdictionary] mutablecopy];   if (!exifd)   {     exifd = [nsmutabledictionary new];   }   exifd[@"aperturevalue"] = @3;   exifd[@"projectiontype"] = @"cylindrical";   exifd[@"xmp"] = @{@"gpano" : @{@"projectiontype": @"cylindrical"}};   exifd[@"gpano"] = @{@"projectiontype" : @"cylindrical"};    resultmutable = exifd;    // log new metadata want written   nslog(@"parameter:\n------------------------------%@\n------------------------------", resultmutable);    // type of image (e.g., public.jpeg)   cfstringref uti = cgimagesourcegettype(source);    // create new data object , write new image   nsmutabledata *dest_data = [nsmutabledata data];   cgimagedestinationref destination =     cgimagedestinationcreatewithdata((__bridge     cfmutabledataref)dest_data,uti,1,null);   if(!destination)   {     nslog(@"error: not create image destination");   }   // add image contained in image source destination, overidding old metadata our modified metadata   cgimagedestinationaddimagefromsource(destination,source,0, (__bridge cfdictionaryref) resultmutable);    bool success = no;   success = cgimagedestinationfinalize(destination);   if(!success)   {     nslog(@"error: not create data image destination");   }    // read , log post write metadata   cgimagesourceref  source2;   source2 = cgimagesourcecreatewithdata((__bridge cfdataref) dest_data, null);   nsdictionary *metadata2 = (nsdictionary *) cfbridgingrelease(cgimagesourcecopypropertiesatindex(source2,0,null));   nslog(@"after:\n------------------------------%@\n------------------------------", metadata2);    // cleanup   cfrelease(destination);    // return new data   return dest_data; } 

as can see directly using nsdata because uiimage stripping exif metadata. code works setting aperturevalue or orientation changes projectiontype ignored.

is setting gpano metadata projectiontype allowed on ios?