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Started: 2010-06-24 08:13:39

Submitted: 2010-06-24 09:02:03

Visibility: World-readable

Sometime around the end of last year, Boulder Linux User's Group's coordinator asked if I would be interested in speaking for an upcoming meeting. I wasn't sure what I'd talk about, but I was confident I could come up with something in the next six months, so I agreed. I blocked out March and April in case I ended up going to India (I did end up being in Darjeeling instead of attending March's meeting), and ended up on the schedule for June.

I spoke for BLUG in April 2004 with the title "Video Editing on Linux: How I made a 45-minute science fiction film using (almost) entirely open source software". I spent most of the six months I could have spent preparing ignoring the talk entirely. I was interested in things like filesystems and Google Chrome OS, but I didn't really know enough to say anything intelligent. I could have researched extensively, and reported on my findings, but I didn't really have the time to devote to that. (One idea did come to mind: A round-table discussion of filesystems with various people who knew exciting things about exciting filesystems.) While trying to fall asleep the night before running the Bolder Boulder, inspiration struck: I know enough about GPS and wilderness navigation to speak at length about it.

I spent most of my free time during the first week of June cramming for the sci-fi book club, trying to finish River of Gods in time for Monday evening's meeting. I could have finished the book in time but for Motoko's battery dying as Kiesa was out shopping for groceries, requiring a late-afternoon trip to Boulder to our favorite mechanic. (To verify that Motoko wouldn't start, I parked her on top of a hill, then got to demo a hill start. I don't know how one would do that in an automatic. Our mechanic quickly diagnosed the problem Monday morning; I biked into work Monday morning and continued into Boulder that evening after work to pick up Motoko.) We ended up canceling the book club due to lack of attendance, and lack of anyone actually finishing the book.

Free of the book club book (which I eventually finished, later in the week) I worked out a quick outline for my talk, starting with the basics of GPS (mostly borrowed from Wikipedia) and coordinate systems, then moving onto how I use my GPS receivers to answer three questions: Where am I; where have I been; and where am I going? I put together a set of demos showing off gpsbabel, Google Maps, Google Earth, and various USGS websites. I barely finished in time for the meeting, and assembled my set of props in front of me, including both of the (functional) Garmin GPS receivers I possessed at that time (a well-worn eTrex Vista for hiking, and a year-old Forerunner 305 for running) and my USGS 7.5' quad of Mount Saint Helens.

I was ready when the meeting started promptly at 19:00, and launched into my talk after the introduction. I prefer to rely on my slides only to show, and to rely on my voice to tell, so my slides were picture-heavy and couldn't be easily interpreted in isolation. I have a tendency to speak quickly when I get nervous; I noticed I was racing through my background on the technology (glossing over the tasty math involved) and tried to pace myself. With another couple of hours to prepare, I could have fleshed out my introduction slides; at one point I forgot which slide I had next and started explaining why longitude and latitude were inappropriate for on-the-ground navigation before I showed the slide with our actual coordinates in longitude and latitude.

I subtitled my talk "How to get lost while still knowing where you are", which was a reference to the gap between having a number tying one's position to an arbitrary reference point on a mathematical model of the Earth's surface, and actually knowing where one was in relation to anything else. Having discussed the theory behind calculating one's position on the planet, the second part of my talk was devoted to demos attempting to make that abstract position meaningful.

I couldn't get a GPS signal inside to show the NMEA output via serial and the more intelligible output from gpsd (answering the "Where am I?" question), so I pressed on to show off my track from my climb of Mount Neva in Google Earth (answering the "Where have I been?" question). (While preparing for the talk, I noticed that gpsbabel had timing information for each point on my track, but it was writing kml for Google Earth with only the timestamp for the entire track. Google Earth can animate timestamped tracks, but gpsbabel wouldn't break up the track into sufficiently-small increments to make that animation useful.) I ran into trouble when I tried to answer the last question, "Where am I going?", using both National Geographic Topo! (running in a VM), gpsbabel, and Google Earth, to draw a line on the map in Topo! and display it in Google Earth. Despite having two gigabytes of core, my computer decided it was out of memory and would rather thrash than let me do what I wanted to do. My demo stalled for five or ten minutes while I waited for VMware to swap in and Google Earth to swap out, and once I was able to show off Topo! I couldn't swap back to Google Earth. I managed to hand-wave my way through the demo and declare something resembling victory, wrapping up my talk in almost exactly one hour.

My audience included some GPS experts; one guy worked on GPS systems for surveying in his day job. I think I managed to be generally enlightening for most of my audience, but I could tell I was bogging down when my computer kept thrashing, making it impossible to actually continue my demo. I intended to assemble static screenshots for my demos, so I could do something in lieu of actually pulling off the real demo.

I think I did reasonably well at my talk. I learned that I need more time to prepare for something this size. (It's tricky to do much of value when I have maybe two free hours to rub together in the evening after work, and when I keep going to bed early to get up early and run. In May I flew to San Diego to give a two-hour presentation for another team at work, and I spent the better part of four working days preparing for it.) Overall, I enjoyed the experience, and I think I could be talked into doing it again.