It’s been several months since I’ve been out for a countryside bimble with a largish group, but that’s now been put right. It was nice to catch up with a few folk that I’ve not seen for ages, whilst exploring nooks and crannies of the Derbyshire Dales — in this case, Tideswell Dale, Miller’s Dale, and Cressbrook Dale, with a diversion to the little village of Foolow to add some variety (and beer).

A bimble through Tideswell Dale, Miller's Dale, and Cressbrook Dale

I chose not to take my camera, so can’t illustrate this post with the small but impressive outcrop of Peter’s Stone (also known as Gibbet Rock — from which the public display of convicted murderer Anthony Linguard’s remains apparently drew crowds from far and wide in 1815); nor the airy view over Cressbrook Dale at elevenses that made the cocoa-pop caramel shortbread taste even better.

However, I was equipped with a GPS Datalogger, whose unblinking geo-locating eye was recording the day’s events, albeit from an unusual perspective. This does beg a question though…

What the hell’s a GPS Datalogger?

A GPS Datalogger is similar to a standard personal GPS receiver (typified by the popular Garmin eTrex devices). Where a Datalogger differs, is that it does away with a screen showing where you are, along with any built-in navigation capabilities such as a “walk this way to next waypoint” arrow, or “x kilometres to go” status messages. Rather, every few seconds, a GPS Datalogger automatically records and saves its position. And that’s about it.

As such, a basic GPS Datalogger isn’t of much immediate use on the hill or down the dale. As a means of recording exactly where you’ve been though, it’s just the job. I should add at this point, that most standard personal GPS receivers also act as dataloggers, enabling you to record tracks of where you’ve been. A bespoke GPS Datalogger just does away with the display and navigation aspects of these devices, resulting in a much more compact gadget. Battery life too, is generally better, given that there’s no screen to power up.

GPS Datalogger (Blumax GPS-4044)

The unit pictured above measures roughly 70mm x 45mm x 20mm, and, in addition to position logging as described above, includes the following features:

• Bluetooth connectivity for uploading position data, or for providing real-time position data to another bluetooth device
• A “point of interest” button, for manually adding waypoints
• Status lights to indicate:
  • GPS tracking status
  • low-power warning
  • low-memory warning
  • bluetooth connection status

In use, one simply has to switch the unit on (ensuring it’s placed in ‘log’ mode), and then forget about it! I’m not going to review this particular GPS Datalogger in detail here — I may do so in a later post, once I’ve put it through its paces a little more — but have already noted the following:

• The unit starts tracking its position within a few seconds of being switched on. This may come as a surprise to anyone used to waiting minutes for their GPS unit to start tracking. Start-up time is greatly reduced by using Assisted-GPS (A-GPS) technology. More about A-GPS another time; for now it’s enough to note that the manufacturer has gone to the effort to support A-GPS.
• The unit seems to be very sensitive when it comes to detecting GPS signals. Much of the walk described above was through heavily wooded areas, and in deep valleys. The unit doesn’t seem to have had any trouble tracking GPS satellites, despite being inside my rucksac lid.
• Build quality is adequate, but no more. This is clearly not a “ruggedised” device. In comparison to a Garmin eTrex, which is carefully designed to deal with inclement conditions (such as being dropped, or exposure to water), this Blumax unit feels very “plasticky”. The “on” switch doesn’t have a very positive action, and feels cheap. I wouldn’t like to guess how long this unit would last if not offered the protection of an Ortlieb map-case or similar.

Using the logged location data

With a position fix recorded every five seconds, a GPS Datalogger can give you a very detailed record of a day’s walk — one that you can peruse at your leisure at a later date once you’ve uploaded the data to your computer. The data upload process is straightforward, and as the data is provided in GPX, format it’s easy to use with all sorts of mapping software.

It’s important to realise that each location record is also associated with a time. This means that, not only can you plot an accurate path of your travels on an electronic map (such as Memory Map, or using an online service such as Google Earth), but you can also review your progress throughout the day in fine detail.

I’ve discussed a number of examples from our walk in the Dales below. The screenshots are all from Google Earth, but remember that the data produced by the unit is in an open format, usable in many different ways and with a wide variety of software.

#1: “Nattering in the car park”

Car park south of Tideswell

First, it’s worth running through how Google Earth is displaying the location data from the GPS Datalogger. As well as the blue “track line”, every location point (one every five seconds) is marked with one of two symbols: an arrow  , or a square .

Google Earth displays an arrow when the following data point is far enough away that a reasonable value for the bearing can be displayed. If the following data point is closer than a threshold distance (a few metres by the looks of it), Google Earth displays the data point as a square instead .

Looking at the plotted track, the different types of markers correspond closely to the speed at which one is walking. A steady pace results in a sequence of arrows, all pointing in the direction of travel. When one slows down, or stops, the symbols change to squares, indicating that the data points are being displayed without bearing data.

So, looking at the image above, we can see the end of the track entering the Tideswell car park as a sequence of (mostly) arrows from the north, and then turning into a bunch of overlapping squares in the car park while everyone stops for a good natter (circled in red). By clicking on one of these squares at the end of the track in Google Earth, each square is expanded out into a starbust of individual points. Clicking on an individual square displays detailed information about that particular data point:

That's a lot of nattering...

Another interesting feature visible in the first image, is that the start of the track (heading south out of the car park), is inaccurate. Even though the unit starts tracking very quickly once it’s switched on, it still takes 30 seconds or so for the location readings to settle down.

#2: “Oops, Wrong Way”

Oops... wandering off at the front

The highlighted area in the above image shows what happens when the walk leader doesn’t keep close enough control of the reprobates at the front of the group — who in this case have blithely wandered off in the wrong direction before being called back. Oops.

It doesn’t take too much imagination to think of circumstances under which this ability to review a route in such precise detail could be quite useful — revisiting one’s progress and performance during a challenge event, for example?

#3: “Which Way Now?”

Up to the right, or straight on?

In the above image, there’s an obvious cluster of overlapping position markers (circled). This corresponds to some indecision with regard to the route ahead. Notice also that, as the track heads north out of the frame, the markers are mainly squares rather than bearing arrows. This is a consequence of slowing down while walking uphill!

#4: “Mmmm, Cocoa Pop caramel shortbread…”

Time for elevenses

The cluster of square markers in this image correspond to elevenses (greatly improved by a Cocoa Pop caramel shortbread “digestif”, and a member of the group expounding on the merits of various supermarket checkout operatives). By clicking on a marker either side of this cluster, we can determine that “elevenses” started at 11:40, and finished at 11:59. Twenty-to-twelveses then. I’ll be writing a letter to the walk leader…

#5: “Stile shenanigans”

Two of the many stiles...

Because the GPS Datalogger religiously records a new data point every five seconds, irrespective of one’s movements, it’s easy to see where “bunching” occurs in the group. The usual concertina effect of a group of ramblers negotiating a stile is clear in the image above.

Whatsmore, with a little detective work, I can surmise that for the first stile (bottom of the image), I was probably at the front of the group. The track there shows no slowing down before the stile, but plenty of dithering on the far side — presumably because I wasn’t sure which way to go. At the following stile, I’m probably nearer the back of the group, evidenced by more hanging about before the stile than after it.

#6: “Lunch and a pint”

Meanderings in Foolow

This image clearly shows the group’s progress through Foolow — lunching on the village green before backtracking to the pub. This is also a good indication of the accuracy of the unit. I reckon that most of the time, the recorded locations are within 3 metres of the actual location when plotted on a map. Of course, this is a very basic assessment, and takes no account whatever of possible inaccuracies in Google Earth’s registration of aerial photography. I can say with certainty however, that, whatever my GPS Datalogger indicates, I didn’t wade across the southern edge of the duckpond whilst looking for a suitable spot for lunch!

Again, timestamps are available for each data point. Thus I can see that we arrived in Foolow at 13:03, sat by the duckpond eating lunch until 13:29, and finally left the village (via the pub) at 14:09!

As a rule, and with only occasional wavering, readings are accurate enough to confirm which side of a road one walked down. Take this example:

Dithering near the A623

Here, the track accurately captures a momentary dither at the middle of this junction, before we chose which side of the road to walk down. Notice also that the location markers are slightly further apart when crossing the main A623 road (between Baslow and Chapel). Reason? A big truck was coming.

#6: “Peter’s Stone, and an entomological/mycological diversion”

Bimbling over Peter's Stone

Our route up Peter’s Stone, and subsequent meanderings on the top, are clearly shown (highlighted in red), as is some dithering shortly after descending the Stone (circled in blue), occasioned by the discovery of Six-Spot Burnet Moths, and some rancid fungus.

Download the data!

The location data can be downloaded from the unit in a standard GPX format, which is compatible with a wide variety of mapping applications. If you want to examine the detail more closely, perhaps using your own mapping software, or even walk this particular route yourself, you can grab the GPX data here (900KB).