The good folks at
SoftRock have kindly
provided us with one of their
SPOT satellite GPS messenger devices to allow you to see where we are
The map you see below showing our current location, is produced in real time and and is updated every 10 minutes (when we are moving). And the pink track shows where we have been in the last 7 days. While this may seem very "cool", the device actually has a a number of very important safety features that will be of great interest to anyone travelling in remote areas. To read more about this awesome little device, visit the SoftRock Spot page at www.findmespot.net.au
NOTE: If the map above does not display correctly (no pink track or no balloon with the latest date and time) you are probably using Microsoft's IE browser - it has a number of bugs that cause issues with Google Maps, we suggest upgrading to Firefox (and yes, I know they will take my MCSE away for saying that.)
Here is a detailed description (for the technical minded among us) of how this map tracks our location (when moving) in real time (10 minute intervals).
When we start the bus, we also turn on the SPOT device and set it to tracking mode. In this mode the device wakes up every 10 minutes and turns on its inbuilt GPS. Once a GPS fix has been obtained (and our longitude and latitude established) the GPS is turned off and the device transmits a tiny burst of data to one of GlobelStars LEO (Low Earth Orbit) satellites that is constantly buzzing across the sky above us. The GlobelStar satellites were launched a number of years ago to support their satellite telephone network. Because the SPOT device has no GlobelStar receiver, it can not be 100% sure that the message has been received, so it sends the same message 3 times (waiting a random number of seconds between each transmission).
Once the signal is picked up by a passing satellite, it is immediately relayed to the SPOT message server. This server determines that the message is not an urgent call for help and simply adds the information collected to its database. If the message had been generated by the press of one of the HELP buttons on the SPOT device, another whole process would start (that may end with a helicopter hovering over our current location).
When you arrived at this page, you set another process in motion ... a custom portion of PHP code running on our web server (written by yours truly) takes a look at the age of the position information stored locally on the server. If this local data is less than 5 minutes old, it builds the Google map you see above from this cached information (and places a (C) below the map to signify that the data came from local cache). If the local data is more than 5 minutes old, the web server sends a request to the SPOT server asking for the latest information (in fact all location information for the last 7 days).
This information is returned as an XML file. The PHP program on our web server extracts the data from this XML file (mucks about with it a bit to do things like turn the GMT time stamps into local time) and creates a KML file (this is the native format used by both Google Maps and Google Earth). This KML file is then written to the local server and the Google map you see above is generated from this KML data (and some manipulation of the Google Java code).
In this case an (L) is placed below the map to show that it was created using Live data directly from the SPOT server (this does not mean that the position is necessarily live - only that the data is the most recent available - if the SPOT device is not turned on, then there will be no update to our position).
When we stop moving, I turn the SPOT device off. Of course it stops transmitting our position and so the date and time shown on the map also stop changing.
If you are interested in Google maps and adding them to your own website, take a look at Mike's tutorial page located at http://econym.org.uk/gmap/index.htm
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