[OSM-talk] Photo_mapping - How to put EXIF data into a jpg image

Jochen Plumeyer jochen at plumeyer.org
Mon Feb 22 02:38:36 GMT 2010


Hi again,

On Dom 21 Feb 2010, Greg Troxel wrote:
> John Smith <deltafoxtrot256 at gmail.com> writes:
> > On 22 February 2010 06:10, Jochen Plumeyer <jochen at plumeyer.org> wrote:
> >> Be aware of your time zone (and daylight savings timezone as well) of
> >> your camera, as GPX times are all in lon=0°/ Greenwich/ UTC/ Zulu time.
> >
> > Actually they are in GPS time, and have an offset in seconds from UTC
> > embedded in the signal.
>
> Huh?  I realize that GPS internally computes in GPS time (!= UTC, !=
> TAI), but I have never seen an actual device output a track log in GPS
> time - it's always been UTC.

I see no difference between GPS and "official" ntp (network time protocol) 
time via internet. 

AFAIK for ntp servers exist drivers to connect GPS as an "official" reference 
time, to distribute and synchronize that time in a network.

So (we are blessed) there is no "time forking". I think the problem is the 
POSIX gmtime() function, the algorithm to calculate UNIX epoch seconds is not 
exact. In our case of photo geo tagging this is no issue I think.
Please tell me if I'm wrong here.

Jochen






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