2004.11.23 12:04 "[Tiff] GPS and EXIF", by Joris Van Damme

2004.11.23 15:56 "Re: [Tiff] GPS and EXIF", by Bob Friesenhahn

I'm trying to find my way through the EXIF specs, trying to add the tags in a new 'Private IFD tags' section of the Tag directory (http://www.awaresystems.be/imaging/tiff/tifftags.html).

What remains unclear is the highest level of understanding on GPS. I see the specified tags, and I see they are clearly related to positioning and satellites and stuff. GPS is then probably the abreviation of 'General Positioning System', I assume. What remains unclear is what kind of application makes use of this. What application or devices write GPS IFDs in a TIFF? Why, what is the purpose? What is the relation to EXIF, that seems clearly to be all about digital camera still images, while GPS includes such stuff as the movement speed and direction? The nature of the GPS tags make me wonder whether there is any relation between GPS and GeoTIFF. Is there?

I am not an expert in GPS or GPS tags in TIFF, however, it is worth noting that many modern cell phones include GPS location capability so that they know where they are (officially to support "911" emergency services). Many modern cell phones also include built-in digital cameras. Therefore these phones may record the location where the picture was taken.

I am not aware of other digital cameras which incorporate GPS although it seems likely that they exist. The GPS tags could also be added via a computer.

Mapping applications could certainly use GPS tags to record the physical coordinates of the map image.


Bob Friesenhahn