Experiments with a GPS Logger (iBlue 747A+)
A iBlue 747A+ GPS logger was obtained to assess it’s suitability as a post-race analysis tool for orienteering. The article discusses aspects of the logger selection and practicalities of use during and after orienteering.
Background and Introduction
Reviewing your route round a course after an event is useful to evaluate how successfully your route choices worked with the hope that some useful lessons can be learnt for future events. It also provides a good social opportunity immediately after a run at an orienteering event. Sometimes (usually when things haven’t gone particularly well!) it’s not possible to work out where you’ve been. This is where a GPS logger can be particularly useful.
GPS: Global Positioning System. A constellation of satellites (which transmit navigation information) orbit the earth and these can be used to determine your position with a suitable GPS receiver (using a system comparable to triangulation). Signals from a minimum of three satellites are needed to calculate a fix accurate to typically less than 10m. The more satellites available: the better the average accuracy. Early tests with the logger discussed below (in Crawley) showed that signals from 7 satellites were easy to obtain, even inside a house. A GPS Logger is an extension to a basic receiver where it records a series of fixes over a period of time. These logged fixes constitute tracks which can be later extracted for analysis.
The rules of orienteering forbid the use of any aids other than a compass, the map, and control description sheet for navigating round a course. Various peripheral aids have crept into the sport and are (currently) tolerated because they don’t provide significant advantage or, where they might, it is assumed that participants apply the spirit of sportsmanship and fairness to the competition and don’t exploit them. Items such as watches, heart rate monitors and GPS trackers (such as the Garmin Forerunner range) may be classed as peripheral aids.
The Garmin Forerunner type GPS devices are well made, but fairly expensive (£100 upwards), and provide more functionality than is really needed to create a simple record of where you’ve been. The displayed information by these devices puts them into the grey area of what can be considered a significant aid and what isn’t, indeed, competitors at international level may find that this type of equipment is banned.
There is a cheaper and less controversial type of GPS equipment, and that is the GPS logger. Examples of these are now readily available for around £50 and may cost half that by shopping around or careful bidding on Ebay.
It’s important to note that technology has improved significantly over the last few years and a good price on an older model may not be such a good deal in terms of performance. The underlying performance of all these loggers is determined by the electronic components (“chip-sets”) that they use, and there are not really many different ones to consider. Current performance leading chip sets are the SiRF III (as used by Garmin in the Forerunner 305 and 405) and the MTK II. There are older SiRF and MTK chip-set about and some less proven brands – these are probably best avoided unless performance can be confirmed. NB SiRF are currently releasing the next generation of their chip-set (SiRF IV), though this hasn’t appeared in any products yet (none that I’ve found in October 2009!)
I decided to take a punt on a sub £30 logger from Ebay – the iBlue 747A+. This uses the MTK II chipset and comes with a Lithium-ion battery, two charging leads and software to interface it to a computer. It is marketed as a photographic aid and features a button that can be pressed when you take a digital photo so that location co-ordinates can be subsequently added to the file that the camera records for each picture.
Initial impressions of the iBlue 747A+ Manufacturers website:
The supplied software appears very functional and fairly intuitive. You need to use the software to configure the logging parameters (update rate etc.) with logger connected to computer prior to use (not possible to do this without the computer). It is easy to download tracks from logger and the magically get displayed on Google earth as discrete tracks! Track editing possible to remove obvious anomalous points.
The logger appears to be more accurate when there is some consistent speed (e.g. tracks recorded during cycling round the town have been cleaner than those recorded during walking. There is some anecdotal evidence (from web) is that early MTK II chip-sets were not quite as good as Sirf III at low speeds (and vice versa) – but this may have since improved and may still be perfectly acceptable for O. Typical track errors of 5-10m would only show as 0.5-1.0 mm on a 1:10000 map – this should be within reasonable bounds.
I easily logged five tracks during one day (approx 1.2-2hrs) and this only consumed 2% of logging memory. It should be easily possible to log any normal multi day O event without having to download data part way through. Start up time to acquire first fix is typically around 15s, and then you’re ready to race! Battery life between charges is said to be 32 hours and it is possible to turn the logger on and off as required – making that 32 hours spread of several days or weeks if necessary.
I have only tried logging normal day-to-day activities so far (it hasn’t been used during an orienteering event – hoping to do that at the beginning of November).
Next things to do:
1) The case is not waterproof and I still need to decide how I’m going to protect it from the wet (simple plastic bag?).
2) Determine how it will be carried for orienteering.
3) Need to confirm performance under tree cover and during rain.
4) Need to try overlaying logger data onto O map. (e.g. in Routegadget). It should be possible to export the logged data as a GPX file for this purpose (direct from the supplied software).
I’ll update this article when I have more to report (after some testing at O events).
Preliminary Iss. Background, Introduction and Initial Impressions 28 October 2009
Posted by Peter Chapman on 28th Oct 09