UTC and .gpx data

[Davo]

Hi all,

i know that .gpx uses UTC (GMT) dateTime, I assume this is a constant at time of track-making, but I have looked at the .gpx file in detail and i can't see how GPSEssentials embeds the timezone offset in the .gpx file? 

i can successfully bring my GPSEssentials track (by emailing the .gpx to myself then importing) into GooGEarth, but i'd say it would be problematic IF googEarth uses lat,lon to get an offest, eg trips near a timezone/over a timezone, local changes to the "official" international timezones, etc.

SO how does a GPSE .gpx track contain information about timezone, therefore the offset from UTC (GMT)?

thanks

dB

[Michael Schollmeyer]

Strictly speaking, the time values in GPX are of type xsd:dateTime which allows ISO 8601 formatted timestamps. In this format, the time zone is optional. I just looked it up and if the timezone is missing, it is actually "undetermined" whereas I assumed it is defaulting to UTC. GPS Essentials is always storing timestamps as UTC internally and only convert it to a local time for presentation. I wonder if any application assumes local time when the time zone is unspecified. Do you have an issue when using Google Earth? I can add "Z+00:00" to all the time stamps but this would bloat the file so I would only do this when something is actually breaking.

Regards, Michael
mictale.com/ms
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[David Bennett]

Thanks for the fast reply. Its bizarre. other than via lat,lon i can't see how googEarth knows how to correctly adjust the .gpx    No there is no need to add any bloat to file size :)

You ask "Do you have an issue when using Google Earth?" at this stage, no. but i have a range of .gpx files recorded at different dateTimes that i need to all finish at the same time.  is there an offset that i can add up in the header of the each .gpx so that will 'offset' the track?

thx

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David Bennett

0416 248 822

www.shapingsuburbia.com