Glenn Baddeley - My Experiences With GPS

• Introduction
• Interface cables and NMEA data analysis
• 'Exploring GPS' book
• Updating from GPS 38 to GPS etrex yellow

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Introduction

I've been interested in GPS technology and its practical uses for more than ten years. I first saw a GPS in action at Buchan in 1992. It was a Trimble Transpack II, one of the original portable receivers, and was the size of a large hard-back book. It depleted a set of four alkaline D-cells with just a few hours of use.

I also witnessed a Garmin GPS45 being used on a Nullarbor Plain caving expedition in 1994, where we recorded the coordinates of landscape features and used it to navigate directly across arid and desert country to isolated and hard to find locations.

It wasn't until September 1998 that I actually purchased a second hand Garmin GPS38. I gained practical experience with that for a couple of years, mainly for recording cave entrance location coordinates and navigating through the dense Australian bush. The GPS38 was first released onto the market in February 1996, so it is quite an old unit. It only has a single channel receiver so it is very slow (3 - 5 minutes) to get a 3D position fix after turning it on.

Interface cables and NMEA data analysis

I have electronics as a hobby and I quickly obtained the plug connector for the power / data output / data input port on the back of the GPS38 and constructed two sets of PC serial interface cables and regulated power supplies for both the car and a mains plug-pack.

I am also a computer programmer. The first effort at writing a GPS program was a versatile NMEA sentence data logging and graphical display program for MS-DOS which was run on an old Toshiba laptop PC. A data analysis program was also written in Visual Basic for Windows 95. I used this to do some investigation of position averaging under varying conditions, and "poor mans" Differential GPS.

'Exploring GPS' book

I purchased the book Exploring GPS - A GPS Users Guide, published by GPSCO in February 1998. It is a very good introduction to all aspects of GPS and its practical use and is especially easy to read. Many illustrative cartoons are included in the 106 glossy B&W pages, which makes it even more appealing. GPSCO appears to be part of the Surveyor General's Department of New South Wales, in Australia. Contact me for details.

Updating from GPS 38 to GPS etrex yellow

Feel free to discuss GPS with me if you wish.

Glenn
Melbourne, Australia.

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