{"id":2568,"date":"2015-05-09T21:46:54","date_gmt":"2015-05-09T12:46:54","guid":{"rendered":"https:\/\/regex.info\/blog\/2015-05-09\/2568"},"modified":"2016-06-05T01:05:39","modified_gmt":"2016-06-04T16:05:39","slug":"the-voodoo-of-elevation-gain-and-strava-and-how-i-got-around-it","status":"publish","type":"post","link":"https:\/\/regex.info\/blog\/2015-05-09\/2568","title":{"rendered":"The Voodoo of Elevation Gain and Strava (and How I Get Around It)"},"content":{"rendered":"\n\n
\n<\/a>\n\nA Light<\/span> Mountain Climb After Lunch<\/span>\n\n340m climb from the village of Kurodani, Takashima City, Shiga Japan\n\u9ad8\u5cf6\u5e02\u9ed2\u8c37\u304b\u3089\u306e\u5c71\u767b\u308a\n<\/div>\n\n

In the screenshot of Google Earth above, you can see the route that I rode<\/span> my\nbicycle last Wednesday... the little bit of green coming in from\nthe right is a downhill<\/span> section of road, followed by the long red uphill section\nthrough the tiered rice paddies of the village,\nthen up the mountain on an old road no longer open to traffic.<\/p>\n\n

I'd ridden 55km (34mi) to get to that point, and would end up riding\n72km (44mi) farther before I got<\/span> home, but ever\nsince my first “<\/span>real”<\/span> ride<\/a> in\nFebruary, I've not been so interested in how much distance I've covered,\nbut rather, in how much mountain I've conquered. This means the important\nstatistic for me is how much “<\/span>vertical\nclimb”<\/span> or “<\/span>elevation gain”<\/span>\nI did<\/span> during a ride,<\/span>\nthe sum of all the rises\/climbs\/ascents on the route.<\/p>\n\n

And it's not just me... vertical climb is often used as a badge<\/span> of\nachievement for a ride,<\/span> and seems to get more talk than distance. It's a strong<\/span> reflection for how tough a route<\/span> is.<\/p>\n\n

The problem is that it's difficult to figure out the vertical climb for\na particular<\/span> route, and commonly-used methods are often wildly<\/i>\ninaccurate.<\/p>\n\n

Cyclers I've met record the ride with a GPS<\/span> unit of some sort\n(their iPhone, a bike<\/span> computer, a runner's<\/span> watch, etc.) and upload the\ndata to Strava<\/a>, a service<\/span> that allows\nyou to analyze your activity and share info about it with others. It's very popular<\/span> and mostly very well done.<\/p>\n\n

For example, I mentioned it in my previous post about a long<\/span> mountain bikeride<\/a>\nthat I did<\/span> on April 30th, where Strava had informed me that I had<\/span> beaten my\nrecord for a particularly<\/span> tough mountain climb:<\/p>\n\n

<\/a>\nData About My Rides<\/span>\nCourtesy of Strava.com\n<\/div>\n\n

Footnote: I've since beat it again, but by only 10 seconds.<\/p>\n\n\n

When you upload your data to Strava, they calculate your vertical climb\nfor the activity, and display it prominently. For example, the\naforementioned first real\nmountain ride<\/a> shows some impressive stats:<\/p>\n\n

<\/a><\/div>\n\n

Since it was my first real ride, I didn't<\/span> know any better but to be\nimpressed by the 3.3 kilometers (2 miles!) of vertical climb that I'd done. I was amazing<\/span>. I was Superman<\/span>.<\/p>\n\n

Unfortunately, it's all a lie.<\/p>\n\n

Over the course of several big mountain rides, I'd started<\/span> to feel that\nthe numbers reported on Strava were quite a bit<\/span> inflated, but I couldn't<\/span> put\nmy finger on exactly how.<\/p>\n\n

A week or so ago I posed about another ride, “<\/span>Short but Intense Bike Ride in Northern Kyoto<\/a>”<\/span>, where someone commented<\/a>\nabout the apparent discrepancy between reality and what Strava reported\n(and hence what I claimed<\/span>). This spurred me into investigating, and I've\nspent the last week digging in, writing tracklog-analysis software, doing\ntests, etc.<\/p>\n\n

So, when I went out on a long ride last Wednesday, I brought<\/span> an\narsenal of equipment with me, recording five separate logs with three\ndifferent GPS\/GLONASS-equipped devices.<\/b><\/p>\n\n

The trip ended up being my longest ride ever, about 125km (78mi), and\nalso had the most vertical climb I'd ever done in one day. Among the many ways I\nrecorded<\/span> the trip's data, I used<\/span> Strava's mobile\napp<\/a> on my iPhone 6+,<\/span> and when I was<\/span> done I had<\/span> the app\nupload all the data to Strava.<\/p>\n\n

Here's what Strava reported about that trip:<\/p>\n\n

\n\nImpressive!<\/span>\nbut wrong\n<\/div>\n\n

The elevation graph at the bottom is an accurate representation of the\n11-hour ride, with four separate major mountain peaks transversed, along\nwith many little ones (though they each didn't seem little at the\ntime!).<\/p>\n\n

Strava informs me that the trip encompassed an impressive 3,627m\n(11,900') of vertical climb. It looks<\/span> like I started<\/span> at about 50m and initially climbed to about\n500m, and from there went down and up quite a bit<\/span>\n— and believe me, I did<\/span> — but looking\nat the graph it's difficult to come up with a 3,637m sum for all the “<\/span>up”<\/span> parts.<\/p>\n\n

In reality, I believe<\/span> the vertical climb on the trip was about 2,225m (7,300').<\/b><\/p>\n\n

First, let's look at why Strava's numbers are so wrong, then let's look\nat how to get a better<\/span> answer.<\/p>\n\n

There are various ways a unit can record your elevation as you travel,\nand all of them are generally untrustworthy. Modern units like an iPhone\nor a dedicated<\/span> unit like a Bad Elf GPS Pro+<\/a>\nhave three methods to figure altitude: GPS<\/a>,\nGLONASS<\/a>, and a\nbarometric altimeter<\/a>.<\/p>\n\n

GPS\/GLONASS can be fairly accurate with your latitude and longitude, as I've discussed in prior\nposts, such as\n“<\/span>Informal GPS Logger Test: iPhone 4s GPS is Shockingly Good<\/a>”<\/span>\nand\n“<\/span>Another Informal Location-Logger Test<\/a>”<\/span>.\nIt's fantastically-amazing<\/i> technology that is perhaps the only\ntime we come in contact with something that must actually take into account\nEinstein's\ngeneral theory of relativity<\/a>. But it's not perfect, and of the three\ndimensions, elevation is by far the least accurate.<\/p>\n\n

Consider these views of three GPS\/GLONASS units' tracklogs plotted in Google Earth,\nof various sections of last Wednesday's ride:<\/p>\n\n

<\/div>\n
<\/div>\n
<\/div>\n\n

The three units rarely agreed with each other on the elevation, nor any\nof them with Google data as seen in Google Earth, and they each in their\nown way tended to wander off wildly at times. (The tracks, when viewed\ndirectly from above, all matched up with each other and the road quite\nwell... it's only the elevation data that was, so to speak, all over the\nmap.)<\/p>\n\n

When wishing to track vertical climb, the absolute accuracy of a unit<\/span> is\nnot particularly important, it's the relative accuracy and stability that\nare important, and it seems that barometric altimeters provide better results.<\/p>\n\n

My first experience with a barometric altimeter, on a Garmin<\/span> GPS unit<\/a> a decade<\/span>\nago, was very bad. If there<\/span> was a breeze<\/span> or you walked with the unit, it\nwould record a non<\/span>-trivial change in elevation (up or down, depending on\nhow the unit was physically angled relative to the air movement). It was ridiculous<\/span>.<\/p>\n\n

Things seem better now. On last Wednesday's trip, I had two<\/span> barometric\naltimeters with me, the one in my iPhone 6+, and another on a Bad<\/span> Elf GPS+.\nHere's their plots for the last section seen above:<\/p>\n\n

<\/div>\n\n

Anyway, a na\u00efve calculation of vertical climb looks at each data point\nand, if the elevation of a point<\/span> is higher than\nthe previous point, add the difference to the total. Minor errors that\nresult in small fluctuations over the short term result in wildly-inflated\noverall results, but one can smooth the raw data (e.g. with a moving<\/span> average) to get more realistic results. That's\napparently what Google Earth does, so let's look at what it calculates for\neach of my five tracklogs:<\/p>\n\n\n\n
Unit<\/th>Type<\/th>Google-Earth Vertical-Climb Calculation<\/th><\/tr>\n
BadElf GPS+<\/td> GPS\/GLONASS<\/td>3,479m<\/td>11,414'<\/td><\/tr>\n
BadElf GPS+<\/td> Barometric<\/td> 2,174m<\/td>7,133'<\/td><\/tr>\n
Garmin eTrex 20<\/td>GPS\/GLONASS<\/td>3,265m<\/td>10,712'<\/td><\/tr>\n
Apple iPhone 6+<\/td>GPS\/GLONASS<\/td>2,215m<\/td>7,267'<\/td><\/tr>\n
Apple iPhone 6+<\/td>Barometric<\/td> 2,009m<\/td>6,591'<\/td><\/tr>\n<\/table>\n\n

That's quite a range of results from the very same trip. Which is correct?\nFrankly, probably none of them.<\/p>\n\n

As we'll see later, there are techniques we can use to eke out some\nfairly reasonable results, but first let's see what Strava actually\ndoes...<\/p>\n\n

What Strava Does<\/b><\/p>\n\n

Strava's iPhone app has access to both iPhone altimeters (barometric and\nGPS\/GLONASS), but in the end it uses neither. Rather, it throws away that\nelevation data and instead relies on its own database of elevation data\n(likely the same data that Google uses to show 3D elevation in Google\nEarth).<\/p>\n\n

Strava's approach may well be fine in generally-flat areas, but it produces\nridiculously-overinflated results in the mountainous areas I've checked, and\nit's easy to see why...<\/p>\n\n

I created some software to analyze the tracklogs, smooth local\nirregularities, and present uphill sections in red and downhill sections in\ngreen. Let's look at the mountain shown in this article's lead photo, a\nlong<\/span> climb followed by a long,<\/span> enjoyable descent down the other side...<\/p>\n\n

Reality<\/span>\n red means uphill, green means downhill\n<\/div>\n\n

Both the climb and the descent were quite straightfoward;\nthe climb was a solid<\/span> climb without any downhill breaks, and the descent was a solid<\/span> descent\nwithout any uphill sections. That's why the ascent is a solid<\/span> red line above, and the\ndescent is a solid<\/span> green line.<\/p>\n\n

Now, let's look at how Strava sees it, as well as all my data sources...<\/p>\n\n

\n\n
\n\nfrom Strava's elevation data\n<\/div><\/div>\n\n\n