Whose turn is it?

We’ve been working for a long time to teach our son how conversation works: we take turns talking and listening.

Similarly, the activities of said 4‐year‐old are represented thus:

links for 2010‐04‐23

links for 2010‐04‐20

links for 2010‐04‐17

GPS and altitude readings

Runners and cyclists can take advantage of some neat GPS technology. It is now possible to create routes, replay training runs, make maps, and compare workouts. Software tools for activity tracking are getting better, and costs are coming down to the point where some good options are even free.

While GPS enables accurate position and speed measurements, elevation measurements are on the weak side because there is a relatively large amount of “noise” in the readings. Even small changes in elevation can be significant to runners and cyclists, especially if running over rolling hills. These smaller fluctuations can be at the limit of the GPS’s ability to accurately measure, and sometimes the smoothing algorithms obliterate all that extra work you did running up and down all those hills. So, more accurate elevation information could give a clearer picture about the effort required.

Some of the tools for working with GPS data from outdoor activities can apply corrections to altitude data. The corrected data usually comes from the National Elevation Dataset, much of which came from the Shuttle Radar Topology Mission.

Out of curiosity, I compared elevation data from my GPS with elevation data from NED on three recent runs in different areas: a 6 mile run in Fishers, the USAF Marathon in Dayton, and the IU Mini in Bloomington. For the most part, they agreed to within a few feet, and the differences fit tidily into a normal distribution.

Fishers morning run mean difference: +1′ between GPS and corrected elevations; standard deviation: 12′

USAF Marathon mean difference: +18′; standard deviation: 14′

IU Mini mean difference: +2′; standard deviation: 19′

To loosely summarize those graphs, my GPS tends to read around 7′ higher than the USGS altitude data. 95% of the time, they agree to within ±15′.

The US Geological Survey claims that the NED data is accurate to within ±7–15 meters (23–49′). That’s about the same accuracy claimed by the GPS, so this is all probably a wash. It looks like it is not practical to get any better data for small elevation changes without adding a barometric pressure sensor to the GPS. Higher‐end cycling GPS units have these, but I am not aware of any running GPS units with barometric altitude sensors.

Uphill and into the wind

Sunday, we took a 3‐hour bike trip up and down the Cardinal Greenway in Muncie. We made a round trip starting at the Depot trailhead in downtown, riding 17 miles to the Losantville trailhead for a picnic at the southern end, and returning.

Emily and I took turns towing David’s trailer. He keeps getting harder to pull. He’s up to 43 pounds, and the trailer adds 23 more. Neither of us could be sure, but it sure seemed to us that both segments of the trip were uphill. To settle my curiosity, I plotted the elevation profile of the trip, and sure enough, Emily’s half was the uphill portion, and I got the downhill. That may or may not have been lucky, since the return half was into the wind.

The net altitude gain on the first half was only 183 feet, but the entire round trip included 791 feet of climbing. “Real” cyclists will scoff, but hey, we’re from Indiana, so it’s not like we see hills very often.

David was a champ as usual, but I think he started to get a little bored toward the end. When we returned to the trailhead, David got to ride his Speed Racer bicycle for a while as I repacked the car and hitched up our bikes on the bike rack. I wish it would have been practical to let him ride more on his own. His time will come, and soon enough, we won’t be able to keep up!

Catherine Mohr Builds Green

In her TED talk, Catherine Mohr Builds Green, Mohr articulates a suspicion I often have when trying to figure out the “right” thing to do by our planet: that there are an awful lot of people “long on moral authority and short on data trying to tell us what to do.”

While these tips may be well‐intentioned, you really have to figure out for yourself what really makes a difference. Often they are trying to get you to buy a new product? Are you missing the elephant in the room? Mohr has an anecdote comparing several different ways for wiping up a spill: using a paper towel, sponge, cotton towel. Her illustration shows a funny obsessiveness with finding out the truth that I can identify with. Some of these truths can be trivial, but there’s still something interesting in the process of discovery.

Then she takes the obsessiveness to the ultimate level by making spreadsheets comparing different building methods for her new house. She writes about the process on her website, 301 Monroe. Her spreadsheet takes a little effort to pore through, but she has clearly put a lot of time into researching the relative effects of lots of different materials used in building a house. For comparison, she includes the effects of other activities that we are more familiar with, such as driving and flying.

Still, is “embodied energy” the right measure for making comparisons? Tons of CO₂? Water use? A different measure could lead to a different “right” choice. Everything we do or use involves tradeoffs, and we should take care that the tradeoffs are worth the worry, and that they make sense. Mohr gives real examples of how the answers are not always obvious!

Spring cleaning

Spring is here, and we’re working on cleaning out the stuff that tends to accumulate for no good reason. Fishers folks have the opportunity to take care of a few “someday” items next weekend, related to Earth Day activities. Since we often miss learning about these events until after they happen, we’re spreading the word a little further.

  1. Fishers Town Hall will be accepting unused medications for disposal on Saturday, April 24 from 9:00 AM until noon.
  2. Shred old documents for a $5 per box donation at the Carmel Police Department the same day from 10:00 AM until 1:00 PM. They will also be accepting unused medications, as well.
  3. While we’re getting rid of accumulated stuff, we’re going to dispose of some paint and other things that don’t belong in the regular garbage. The Hamilton County Household Hazardous Waste Center accepts these items on an ongoing basis on Saturdays from 8:00 AM until 1:30 PM, and they have weekday hours as well. Indianapolis residents can take advantage of their own Tox Drop program at various locations and times.
  4. Only peripherally related, since it’s one of those recurring things that tends to get brushed aside: check those smoke detectors! Buy yourself some precious extra moments in an emergency. We’ve seen too many house fires.

A use for Wolfram Alpha

Wolfram Alpha, the infamous answer in search of a question. Today I actually got a useful answer out of Wolfram Alpha! I was working on a project to correct altitude information from my GPS watch, and I needed a sanity check. Looking at exported data from Ascent, I wasn’t sure whether Ascent had exported altitudes in feet or meters. Wolfram Alpha reassured me that I was indeed working with feet. Whoopee‐doo!

Unfortunately, for a service that was hyped to revolutionize the way that computers “think,” this seems like a hopeless waste of engineering effort.

links for 2010‐04‐13