GPS INDEX PAGEChoice of GPS for use in Road Race Course Measurement

Consumer GPS units can now be obtained quiet cheaply, and because many users update to a new model with the latest features, basic units are even cheaper when purchased second hand or at a discount on places like Ebay. The problem faced by the new user is the overwhelming choice and difficulty to determining what features will be needed. I was greatly helped by advice from Phil Holland who, having used various Garmin models on his measuring bike and also for hiking, was able to guide me quickly to the Garmin Etrex model H.

The Garmin ETREX H is a basic handheld model which has the latest high sensitivity chip set. It comes in a bright yellow water resistant rubberised case (see picture above). The operating buttons - two on the right three on the left do need quite firm pushing and navigating its menus is not as slick as the more expensive Garmin models which have a small joy stick. It does not have the following features, which Phil advised me I would find little use for in course measurement:

mounting clip &interface cableI found the ETREX H was selling in the cheaper shops: for £72 at the local Go Outdoors outlet and up to £84 elsewhere. However, I got one on Ebay for £45 which seemed as new in the original box. I have just checked Amazon and they have a good number of suppliers with prices ranging upwards from £65.

Next I needed to connect the unit to the serial port on my computer. The lead with a car power adapter was £10.

Then I needed some software to download the recorded data onto my PC. Phil strongly recommended the powerful and very comprehensive GPS Utility package. I started with the free trial version. This enabled me to download up to 100 way points, 500 track points, and 5 routes, but despite this limited capacity it allowed me to get started. My first impression of the GPSU software was that it was rather clunky or at least not completely intuitive at leading you to achieve your objective by just navigating the menu, and not taking time to read the comprehensive help files. Persistence and practice has paid off and one month later I have learnt how to make GPSU do most things I need to. However, I am still discovering new features. It was not long before I paid my £30 registration fee and got full access to the full size data file capabilities of GPSU, which include handling of 500,000 track points.

bike mountFinally I needed to get a proper mount to attach the ETREX to my handle bars. The cheapest I found was from Go outdoors for less than £10. You just remove the battery cover and replace it with one with a clip that connects to a socket which mounts on your bike handle bars. Removal of the ETREX from the bike is now very quick and easy, I have thrown away the gaffer tape which I used as a temporary bodge.

Total equipment outlay: £95

You can spend a lot more on consumer type GPS equipment, but I doubt that more expensive kits offer anything much that would be useful to me and certainly are not likely to have improved accuracy over this model.

Of course being a measurer, I would like to have GPS equipment designed for professional survey, which could give me improved accuracy. If I had a beacon receiver, I could use to correct for local errors or else if I had a dual frequency receiver, I would be less sensitive to ionosphere and multipath errors. Doubtless such equipment would improve accuracy by more than a factor of 10 if I gave the unit time to average out noise. But for now I think I will have to wait for prices to fall, or else understand enough about how it works to be able to select some cheap equipment.

Mike Sandford - 31 October 2009