One thing I just noticed is that non-coordinate GPS tags aren't as flexible as the coordinate tags. For example, you can't write
C:\>exiftool -P -overwrite_original -GPSImgDirection*="336.6 True North" y:\!temp\Test4.jpg
Warning: Can't convert GPS:GPSImgDirectionRef (not in PrintConv)
Nothing to do.
I wouldn't think it would be high priority and not worth it if it was difficult, but something to consider.
The main reason the GPSLatitude/Longitude tags have the extra "smarts" is so they may be written from the corresponding XMP tags, which have the hemisphere included. But the XMP tags for GPSImgDirection and GPSImgDirectionRef are still separate, so this wouldn't help when copying tags, and not many people would think of using a command such as you have given to write both from a string value.
- Phil
Ah, I see. Good enough then.