How does the Garmin eTrex H navigate routes?

3 February, 2011

I hate not knowing how something works. My childhood is littered with electronic devices pulled apart and analysed … radios, motors, cameras, computers.

I couldn’t figure out how the eTrex navigates along a route so I had to run some field tests which for a GPS unit means going for a walk. The first few tests were inconclusive so on the way to work this morning I walked along a 3-point route and checked how the Garmin calculated the next waypoint at four points along the route: before the route, between the first two waypoints, between the second two and after the route. I checked it both ways, so following the route to the northmost waypoint and then to the southmost, so eight datapoints all up.

The results are depicted in the diagram below; the results for following the route south are the same as the reverse of following the route north so I’m just showing the four scenarios here:

Garmin eTrex H route navigation map.

The eTrex assumes that you are standing at the first waypoint so it doesn’t bother to navigate you to the first waypoint. Whilst you can create a two-waypoint route it doesn’t really make sense as it will navigate directly to the second and final waypoint so you might as well just GOTO that waypoint – except that if you have the two waypoints as a route you can see a line between them on screen which might help you orient.

The Garmin eTrex chooses which waypoint to send you to depending on where you are in relation to the waypoints. If you’re closer to a waypoint further along the route it’ll just skip earlier waypoints and won’t make you U-turn.

In this following additional test I walked past the second waypoint instead of going to it. Once the eTrex determined I was giving the second waypoint a miss bypassing it by 70 meters it switched over to the third and final waypoint:

Garmin eTrex H route navigation map.


Data, glorious data!

5 January, 2011

Took my new Garmin eTrex H GPS out for its first spin today on a short walking track behind Hawker:

Trip stats:

Distance: 1.72 km
Speed: 5.6 km/h
Time: 00:18:13

The main purpose of this test run was to figure out the difference between Track Active Log and Saved Logs. The Active Log contained 90 trackpoints (89 once I removed the one it plotted when I turned it back on at home to download the data), yet the compressed saved log had only 16 trackpoints, although the plot of the saved track was good enough and only deviated from the full log by up to 8 metres and that only in a few places. It’s an irrelevant discrepancy as even the raw data points deviate from the actual coordinates by up to half that (at 4 metre accuracy) which means most of the time the simplification of the track by compression actually corrects tracking error. Swings and roundabouts.

It is true that the eTrex strips out date stamps when compressing a saved log so I guess you can only use the Active Log to geotag photos with ExpertGPS’s batch geotagging feature which matches up photo date stamps with your track’s and injects the GPS coordinates for the corresponding time (important to make sure your camera clock matches your GPS’).

Here’s a plot of my track, all 89 trackpoints taken at 20 metre intervals:

Hawker ACT track in Google Earth.

Sample trackpoint data.

Interactive map of track start:

Even though I probably should have been doing other things considering I’m moving overseas in two days I’ve spent much of the past week playing around with NZ LINZ topographic maps, GeoTIFF calibration, TWF formats, KML and plotting out routes I’d like to tramp when I get to New Zealand. Even wrote a Greasemonkey script with the help of James Peek to convert KML LineString strings to a suitable CSV format for GPSVisualizer’s GPS to GPX converter so paths drawn in Google Earth can be imported as waypoints or routes into GPS mapping software.


How should I do this formatting?

3 January, 2011

GPS Visualizer has this great tool for converting a GPS file to GPX but I have an unorthodox need for it: to convert a comma-separated list of coordinates from a LineString element out of Google Earth.

Google Earth copies elements as KML so you can copy an element such as a path from Google Earth and paste it into a text editor. Locating the LineString element in the XML is relatively easy but it would be nice if there was an easy way to convert the single string into the proper CSV format needed to run it through the converter (shame Google Earth doesn’t write GPX natively).

This is what a LineString looks like (no line breaks):

172.2384849468256,-41.46954787285365,0 172.2432306652765,-41.46826502144933,0 172.2482385664333,-41.47388161005981,0

This is what I need to plug into the conversion tool (with line breaks):


I currently do this manually by:

  1. Copy LineString string of coordinates out of pasted KML and into a new text editor instance
  2. Search and replace ,0  with \n
  3. Copy and paste into Google Docs spreadsheet (which has default waypoint names and column headers)
  4. Copy whole spreadsheet back into text editor
  5. Search and replace \t with null

It’s a bit time consuming and putting me off from plotting routes in Google Earth, and is prone to error so some macro or something that can do this simple step automatically would be great.



Triple J Hottest 100 2010

27 December, 2010

My shortlist, with the 10 tracks I voted for in bold:

  • Art Vs. Science – Magic Fountain
  • Ash Grunwald – Lady Luck
  • Avenged Sevenfold – Nightmare
  • Bamboos, The – Turn It Up {Ft. Lyrics Born}
  • Beautiful Girls – Don’t Wait
  • Boy & Bear – Fall At Your Feet
  • Cee Lo Green – Fuck You!
  • Crystal Castles – Not In Love {Ft. Robert Smith}
  • Cypress Hill – Rise Up {Ft. Tom Morello}
  • Delphic – Doubt
  • Digitalism – Blitz
  • Florence & The Machine/Dizzee Rascal – You’ve Got The Dirtee Love {Live}
  • Flight Facilities – Crave You {Ft. Giselle}
  • Gorillaz – Stylo {Ft. Bobby Womack and Mos Def}
  • Gotye – Eyes Wide Open
  • Mark Ronson & The Business Intl – Somebody To Love Me {Ft. Boy George & Andrew Wyatt}
  • M-Phazes – Goodbye Gravity {Ft. Muph & Plutonic/Candice Monique}
  • Naked And Famous, The – Punching In A Dream
  • OK Go – This Too Shall Pass
  • Pendulum – Witchcraft
  • Raekwon – Kiss The Ring {Ft. Masta Killah & Inspectah Deck}
  • Sia – Clap Your Hands
  • Stonefield – Through The Clover
  • Subs, The – Kiss My Trance
  • Subs, The – Mitsubitchi
  • Washington – I Believe You Liar
  • Yolanda Be Cool/DCUP – We No Speak Americano

2010, a year of healing

27 December, 2010

As I suspected in my wrap-up blog post for 2009 this year was about a deeper recovery from my upbringing in a toxic cult. I didn’t know or accept it at the time but having now been through several months of psychological counselling and on a prescription for anti-depressants I now realise that my sense of that ‘something beneath the surface’ was depression. So the first half of 2010 was all about therapy and recovery: exploring my past and dissolving the mental and emotional scar tissue to become a more functional, whole and contented person.

The change after therapy and starting medication was so drastic that Jenny now refer to the history of our relationship as two eras: Before Medication and After Medication, although of course the drugs were only part of the solution. We don’t like to talk about the dark days of Before Medication.

So while 2010 has been pretty awesome in that regard the first half was a bit rocky. My psychologist had me in tears every session and I’d need to take time to pull myself together before going to work. It was hard work but bloody worth it. One of the more tangible outcomes of the therapy is that I now have a much better relationship with my dad; I no longer bear a grudge for his part in my being brought up in a cult and how much work he created for me in leaving and recovering from that place. Just evidence of how I’ve come to terms with my past and integrated the first 25 years of my life into who I am now rather than shunning that part of my life as something I’d rather forget. Like alcohol on a raw wound, it was a painful process but I’ve come out of it healthier and stronger.

I still want to write a book about my experiences growing up in a fundamentalist Christian cult but I’ve put that on the back-burner till I get to New Zealand. I think I’ll have a lot more spare time, less distractions, easier to focus on a big project like that. The change of scenery should help inspire me too.

Oh yes, in case you didn’t know we’re moving to New Zealand next year! In fact I’ll be flying over on the 8th of January and starting my new job on the 10th – you can read more about that on my new NZ blog.

Looking forward, 2011 is going to be pretty awesome but won’t be without its challenges – moving overseas, living in a new country, leaving behind most of our stuff and creature comforts, making new friends, adjusting to a new culture, starting a new job, transitioning from government work to private sector … but they’re all challenges I fully embrace and look forward to. I think 2011 will be amazing and this graph of personal growth and life experiences that started in mid-2008 for me is showing no signs of slowing! Maybe 2012 will be a bit quieter, though not if I have anything to say about it!


WTF Virgin Blue?

24 December, 2010

My email I just sent Virgin Blue:

I was booked on a flight in November 2009 which Virgin Blue cancelled at the last minute forcing me to quickly book a flight with Qantas at over $100 more. I was told I could quote my reservation number for a future booking to receive a credit but I tried to claim that credit today and was told that my credit has expired. I don’t understand how this is possible – that was my money and you’ve just taken it without providing the service. I’m seriously annoyed. I don’t care what your legal rights are; I don’t want you to quote legal fine print to me … you fucked me over, that’s all there is to it. Not happy.

UPDATE: Virgin Blue has responded to my email on 7 January. The language is painfully formal but the short story is they’ve reinstated my credit of $79 for the flight they cancelled on me in November 2009 and extended it for another 12 months. I didn’t expect that so it’s a pleasant surprise. Now I have to make sure I come back from New Zealand in the next 12 months so I can use it!


Back on Facebook, sort of

20 December, 2010

I still stand by my reasons for leaving Facebook but with me leaving for New Zealand soon I need a way to keep in touch with my friends who aren’t on Twitter. So I’ve joined Facebook again but will only have a barebones profile and my only posts will be tweets syndicated through the Selective Tweets app that have been tagged with #fb.


I will not be actively using Facebook, I will not be logging in and people can’t post comments on my wall. But at least I have some sort of presence there now so you can follow me and feel free to drop me a note at nboehm@purecaffeine.com or on Skype nathanael.boehm to chat.