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January 29, 2007

Edge versus Vista (2)

Filed under: GPS — mtbguru @ 12:52 am

This is not a rematch, but some additional data highlighting the difference that the SiRFStar III chip (Edge) makes.

Previously, we noted that the accuracy of the Vista goes down significantly when under canopy or in narrow canyons, whereas the Edge was holding up very well. Most of the route in the previous test consisted of trails in open meadow land with some relatively short forested sections.

But when the trees are getting really dense, things become more pronounced. The Vista may start to lose signal – you’ll notice this when the track log is broken up in several sections. I took both units on another local ride (Alpine Road in Portola Valley to Skyline Blvd), this time mostly under dense canopy and/or skirting a fairly narrow canyon.

The first graph shows longitude versus latitude – the Edge recorded again a very clean track, whereas the spread on the Vista was large, and included several drops in signal. The route was done out-and-back.


The image below shows a section of the track recorded by the Edge, overlayed on a satellite image in Google maps on which the trail can be seen, hinting at the Edge’s accuracy. Of course, this isn’t saying much since this section of trail was obviously visible by a satellite (which would not be the case in really dense sections), but it does give an idea.

Alpine Rd

Interestingly, looking at cumulative distance over time (graph below), a lot of the spread in the signal is again averaged away, as mentioned in the earlier post. Except for the signal drops which may show up as small anomalies, the Vista produces pretty much the same data as the Edge. So even a GPS having crappy reception can still make a decent odometer… but not a good tracker.


January 28, 2007

Garmin updates: Training Center and the Superbowl

Filed under: GPS — mtbguru @ 10:08 am

Garmin Training Center for Mac OS X can now be downloaded from their site, and there is also an update for the Windows version. In related news, coming Superbowl weekend Garmin will be sporting a second-quarter ad, featuring – besides a muscular marketing budget – a battle between a ‘Maposaurus’ and the ‘Garmin Man’ – check it out on this Youtube preview on GPS Tracklog.

Our favorite Mac GPS tools remain GPSBabel+, LoadMyTracks and Routebuddy (the latter as soon as they’re supporting GPX), which all work or should work with Garmin devices, but it’s nice to see some progress from Garmin itself.

January 25, 2007

New cycling discipline?

Filed under: Riding and racing — mtbguru @ 7:27 pm

Here a GPS probably would turn out to be more accurate than a wheel odometer…

January 23, 2007

Comments and comment notification

Filed under: Howtos / tips / tricks — mtbguru @ 9:12 pm

When you create a trip on MTBGuru, you can enable other users to add comments by adjusting the ‘Trip Settings’ in the sidebar (see screenshot below):


Click ‘Change’, then switch the ‘Allow Comments’ field to ‘Everybody’.
By default, comments are enabled but only registered users of MTBGuru can leave comments, in order to avoid comment spam.

If a trip is public, also its comments will be visible for anyone visiting the site.

You can get notified by e-mail when someone left a comment on one of your trips by our ‘Comment Notification’ feature. Go to ‘User Settings’ (sidebar), and you’ll find the ‘New Comments Notification’ field (screenshot below):


There are three settings. ‘Never’, in case you don’t ever want to receive a notification e-mail, ‘Immediately’, so you’ll receive an e-mail for every new comment that gets posted on one of your trips, and ‘Max. once per day’, then you’ll receive at most one notification e-mail per day. The latter is the default setting.

Leaving comments works pretty much like leaving comments on blogs – you can use html tags to insert hyperlinks etc. Moreover, we also support Textile, a very simple and elegant text markup language. More about that in a later blog post.
Finally, trip owners have of course the ability to delete comments on their trip.

Update 6/19/07: There seems to be a bug at work preventing deletion of comments – we’ll try to fix this asap.

January 19, 2007

Edge versus Vista

Filed under: GPS — mtbguru @ 8:41 am

I recently did some field testing in order to compare my two GPS units, a Garmin Edge 305 and a Garmin Etrex Vista. Note that none of us at MTBGuru are affiliated with Garmin in any way, these just happen to be the units I own and generally like: the Edge is a good cycle computer, and with its SiRFstar III chip an excellent track logger. My Vista is a bit older, has a less sensitive GPS receiver chip and some other annoyances (such as dropping time info when saving tracks) but you’re able to upload topo maps which you can view on its big display, so for navigation the device is pretty good.

What did I want to find out? I already knew the Edge had much better reception under canopy, in wooded areas or narrow canyons. In these circumstances, the Vista would sometimes lose signal, with interrupted tracks as a result. The noise on measured latitude and longitude on the Vista is higher – how would the measured distances compare?
I was also interested in how the two altimeters would compare. Both units have a barometric altimeter. The Vista’s altimeter can be used in two modes: ‘auto-calibration’ on or off. When on, this auto-calibration uses elevation data based on the GPS signal to periodically recalibrate the sensor (about every 15 minutes). When off, it’s the barometer only that produces the elevation measurement.
In addition to this, you can also manually calibrate the altimeter (useful if you know the altitude at which you’re at). The Edge on the other hand features a barometric altimeter that is quasi-continuously being recalibrated based on its GPS-signal.

So I went for a ride with the two devices, up in the Santa Cruz mountains. From the Russian Ridge parking lot on I started logging, and headed up to Borel Hill:

borel hill

I hadn’t used or calibrated the Vista’s altimeter in a while and it was initially quite out of whack (about 400 feet).
At the summit of Borel Hill, 2572 feet high, I manually recalibrated the Vista and set ‘auto-calibration’ to off. In the meantime, the Edge was giving me the right altitude within 10 feet.


The graph above shows the raw elevation data from both units over the whole ride; the interesting part is that after being recalibrated on Borel Hill, the Vista’s barometric altimeter (without GPS ‘auto-calibration’) tracks the altimeter from the Edge almost perfectly. This is not too surprising: though they are in absolute terms not very accurate and require frequent recalibration, altimeters have very good relative accuracy and over a time frame of a few hours won’t drift much. A weather front that suddenly moves in is about the only thing I could think of that would knock it off quickly – otherwise baseline drift is a very slow effect. And I have actually still to experience any such effects attributed to fast-moving weather fronts; but then I live in an area where we don’t see much of these.

On the ride, I repeated the same section of trail multiple times – I did the same descent and climb three times, as an out-and-back. The graph below (a blow-up of the first graph) illustrates this:


The red dotted line connects points that represent one single spot: the top of the climb. The extra bump on the second peak is to be ignored, as I climbed there a bit higher to a ridge to take a break. At the third peak I took another quick break and played a bit with the controls of the Vista – that may explain the weird little dip in its signal. But as you can see, drift over the course of about an hour is minimal (less than 10 feet), and consistency of the data is quite good. Only at the third repetition of the climb, a slight deviation between the two units can be observed.

So concerning elevation, the two units aren’t very different. The Edge’s altimeter is just much more convenient because you don’t need to recalibrate – the ‘quasi-continuous’ automatic recalibration seems to work well due to its very accurate GPS signal. I used the Vista here with ‘auto-calibration’ off, because I wanted to rule out sudden shifts that would occur every 15 minutes. On another occasion, I’ll look at the effect of the latter. I will also keep the discussion on cumulative elevation gain and loss numbers for later – these are a function of the noise of the sensor and the filtering applied.
Other interesting data to look at would be the pure GPS elevation data but neither of these two devices allow extraction of such data (I’d need an Edge 205 or Etrex Legend which don’t feature a barometer to obtain this).

The difference in accuracy of the GPS-signal between the two units can be easily observed by plotting out latitude and longitude against each other (figure below) – this is the same descent+climb repeated three times as in the previous figure:

EdgeVista lat long

The graphs plotted here consist of an overlay of six times the same track segment (three times down and three times up). The spread on the Vista’s signal is clearly larger than the Edge’s, in particular around the area on the right, indicated by the red dotted circle, which was a section of trail under fairly dense canopy. Note that the Vista did not lose signal here – in other conditions where it would do that, the signal would of course be messed up even more as a number of points would be missing.

How does this translate into distance? In a way, distance is ‘cumulative location’; you’d expect that things will average out a bit, and indeed, if you plot distance versus time for the same 3x repeated track segment, you’ll see the Vista and Edge returning roughly the same graphs:


The slope of this curve is of course the speed, and you can quickly identify the descents, climbs and breaks. Distance is calculated from latitude and longitude using the great circle distance formula as mentioned in another post.

In conclusion, both devices are about equally good in generating elevation and distance data (with the Vista having a calibration issue), but for logging tracks the Edge’s SiRFstar III chip is quite superior. Another unit, the GPSMAP 60Cx seems to combine the best of both worlds, but it comes at a higher price, and in a bulkier package.

January 15, 2007

New blog for GPS users

Filed under: GPS — mtbguru @ 11:40 pm

Free GeoTools is a new blog that focuses on tools, tips and tricks that can make life of GPS users easier… without making them spend big bucks. Something that we here at MTBGuru also strive for.

Btw, this prompted me to update this blog’s link lists in the sidebar – I’m planning to add more in this space soon.

GPS markets and trends

Filed under: GPS — mtbguru @ 10:05 pm

Some interesting reading material on GPS markets and trends:

This U.S.News article talks in great detail about Garmin, its history and future – possibly a quite bright future. An interesting bit from this is that worldwide TomTom and Garmin are currently shipping about the same number of units. And more competition is on the horizon (besides a number of smaller companies, also giants such as Sony are stepping into the GPS market, to be followed perhaps by smartphone producers such as Motorola and the likes, or even Apple). This is probably good news for users, who I’m sure wouldn’t mind seeing some of the quite hefty prices drop.
(via GPS Tracklog)

And this Yahoo News article mentions how bluetooth chip producer CSR has acquired two smaller GPS IC design companies, a move that could indicate we’ll start seeing more and more GPS functionality in various mobile gadgets.

January 12, 2007

Mapping at Macworld

Filed under: Google Earth,Mapping — mtbguru @ 12:21 am


Steve and friends were in town again, and they made sure everyone, in particular those attending CES in Vegas, would hear of it – we went for a quick visit to the Moscone Center to see if any interesting things are happening in the Mac world related to GPS and mapping.

Garmin of course announced the OS X version of Training Center, which was being showcased at their booth.
Garmin booth
Unfortunately, Training Center is the only thing available on OS X, for the much more useful MapSource there is still a wait.

Google had a pretty large booth, entirely focused on Google Earth and 3D drawing tool Sketchup:
Google booth
The Mac version of Google Earth was celebrating its first birthday here.

In pre-Google Earth times, 3D Weather Globe & Atlas by MacKiev Software was the ruling 3D mapping software – they’re still around, and offer for a yearly subscription a real-time data stream that contains for instance current weather information.

Garmin competitor Globalsat was showcasing a number of soon-to-be-released devices, one of which looked very much like Garmin’s Forerunner 301/305 model, a wrist watch GPS device targeting outdoor sports and fitness folks. They were teaming up with software makers Routebuddy, who’ve created a nice mapping tool for OS X – it would even be nicer if it would support a standard output format such as GPX; they promised me that was coming soon.

There was of course only one star on this show:

iPhoneiPhone demo 2
The iPhone’s excellent screen looks perfectly fit to display maps. In fact, it looks so good that I’m quite disappointed that the thing doesn’t have a GPS built in – as I was getting a bit carried away imagining this:

iPhone on bar

Endo’s could become expensive though…

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January 10, 2007

Uploading trip data to your GPS

Filed under: GPS,Howtos / tips / tricks — mtbguru @ 10:51 pm

In a previous article we talked about some tools to download data from your GPS unit and save into GPX files. Now we’d like to outline what you can do with GPX files you’ll find on MTBGuru (which aren’t necessarily yours).

For each public trip on MTBGuru that has GPS data, you can download the associated GPX file (using the ‘Download GPX file’ link in the sidebar) as well as a Google Earth (KML) file. By browsing around the map, using the search box or by clicking the ‘Recently Added Trips‘ link you may find a trip or ride that catches your interest. Say you want to do this ride yourself: the trip summary gives you an idea of what to expect in terms of distance and elevation gain and if there’s timing info you’ll know even better what you’re up for. You can now use the GPX file to send the data to your GPS unit, so you’ll be able to retrace the given route.

Some units allow a straight upload of the entire GPX file with its waypoints and tracks. In some cases though, there are complications:

  • For instance, on some Garmin units (e.g. the Etrex family) the size of tracks you can upload is limited to 500 points (even though they can *record* tracks of much larger size) – larger tracks will be truncated
  • Some units don’t allow upload of tracks, only waypoints and/or routes

A quick GPS terminology 101 may be in place here:
A ‘route’ is a sequence of waypoints that indicates a certain route. A ‘waypoint’ is basically a set of three numbers (latitude, longitude, elevation) indicating a point in space, usually on the surface of the planet ;) . A track is a sequence of (recorded) waypoints but generally also contains time information.

GPX files you download from public trips on MTBGuru contain tracks. The time info in this file is stripped but all spatial information (long,lat,ele) from the trip is available. Only trip owners have access to the time info in the GPX – using the ‘My GPS Files’ link in the sidebar they can always retrieve the original uploaded data.

As mentioned before, uploading these files directly to your unit can sometimes result in truncated data and other problems. However, you generally don’t need that many points to navigate and retrace a given trip. You can use a host of software tools (e.g. Garmin’s MapSource on PC, Routebuddy on Mac OS X) to create routes with a limited number of points from tracks and upload these instead.

GPSBabel filter

Our favorite tool, GPSBabel, has a very neat and simple way to achieve the same: by using its ‘filters’ you can automatically reduce the amount of points in a GPX file. Select your GPX file as input file and set up your filter as shown in the screenshot (using distance between the points as filter); the output file will be a GPX file with a reduced number of points. You can change the amount of points by changing the merge distance between points.

January 7, 2007

Trip name, tags, photo titles

Filed under: Howtos / tips / tricks — mtbguru @ 11:24 pm

These three items on your trip page have in common that you can edit and change them on the fly, by hovering your mouse over them, clicking and typing.

What makes this possible is a technique called ‘Ajax inline editing’. Most people will associate the word ‘Ajax’ with the cleaning product, the Dutch soccer team or the Greek hero – but in web development circles it’s the name of a cool and hip set of techniques (acronym for ‘Asynchronous Javascript and XML’) to make web sites more responsive, interactive, intuitive and usable. The word is almost continuously being dropped by Web 2.0 marketing types, in buzzword-bingo worthy fashion, but it can truly make a difference.

For instance, let’s see how you can edit trip names. On the trip page, hover with your mouse over the trip name field – you’ll see it light up in yellow; and after a second or two, a tooltip appears (the ‘Click to edit’ box):


Then, if you do click, you’ll see this edit box appear, together with ‘ok’ and ‘cancel’ buttons:


You can now simply type in or edit the trip name and press enter or click ‘ok’.

The same works for the tags, as well as for the photo titles; the latter can be used to add some lines of commentary underneath the photo thumbnails, as shown below:


The stuff that lights up in yellow is material that you can edit right away by a single click.

Without Ajax, you’d have to work with links or click buttons that reload the entire page, with forms and other clunky remains of the earlier days of the web. One drawback of the Ajax approach though is that web site visitors are generally not yet anticipating this kind of interactivity and may overlook it – hence this post.

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