I notice that the quicktime::itemlist\1.3\gpscoordinates tap is read-only. can anyone tell me what other metadata/tags are used to populate this one? thank you
This is a proprietary Apple tag I believe. If it is marked as read-only, ExifTool has declared it so. I would not dabble with proprietary Apple tags anyway.
You can use normal XMP GPS coordinates in IMatch with QuickTime files, IMatch can read and write them. The map panel uses them, reverse geocoding works etc.