Run data, run data, run data. When will it EVER end? Probably with this post, is my guess. After this, well, I think I may stop harping about it, and simply enjoy the time outdoors and not worry about elevation profiles.

I recently started putting my run data on RunningAhead.com. I really like the site and the ability to graph multiple elements simultaneously on a single graph. I also like that it reads the data from my Garmin Forerunner 405CX wirelessly, too. That makes data upload easy. The only thing Garmin has on their site that I still occasionally look at is goal-progress. I imagine RA can implement that one pretty easily too, and eliminate any need for me to deal with Garmin.

When I uploaded some of my data, I noticed that, yet again, the elevation profile information was different from everyone else's. As part of a different conversation with Eric Yee from RunningAhead, I asked about why there were differences in elevation profiles for different sites. This is part of his response:

Wow. Google is different. I also think there is a fudge factor at play on some of my runs in the data itself. If, for example I am following a trail on the side of a fairly steep hill, the trail may be in fact "flat" as it is following the contour. However, the GPS is not ever spot on, and it may be tracking a point 20 feet to the right, then 5 feet to the left, and so on. On a steep hillside, that 20' right might be 15 feet higher than I am, and the 5' to the left may be 10 feet down. So in the course of my movement of 10 feet straight ahead, and level, the GPS just might have tracked a 30' loss of elevation. Or so it seems to me.

At any rate, have a great weekend. My loin-fruit are free of school as of this afternoon, so they'll be as happy as I am tomorrow: they get to sleep in, and I get to go for a run before the big 13th birthday party for my son. O_O

I use Google Earth a lot to view places, plan runs and create elevation profiles for the entries in this blog. While I was putting together the latest run entry, I noticed something odd about the elevation profile information. It changed. The same kmz file provided different elevation profiles -CONSTANTLY. I looked at the run on a Mac, and then on a PC. Different. I looked at the run on the PC at different window sizes. Different again for each window width, for both distance, and elevation gain/loss.

I don't get it. The data are a series of XML latitude and longitude points. The earth itself doesn't change based on the viewer used to see it (boy, that would be weird), so why would the elevation profile change between what is used to look at it? I guess there is no way to truly extract the accurate elevation profile information from any of the tools I have access to, considering there is a difference in Garmin's interpretation of their own data when the information is presented on their website as either a route or a course.

Google Earth: a reality distortion field. In this case, if I wanted my elevation profile to appear to be more of a challenge, I simply stretch the X-axis of the graph by increasing the width of the window and it happily accommodates me, making both the distance and the elevation changes appear greater on the screen. Selecting "Get Info"/"Properties" on the file in the places list and then selecting the Measurements tab shows the same for the length, so at least that seems to be static. 

The data from the run is shown in the following images, with the screen grabs from the same kmz file. I wonder if it is simply a factor of revealing more information, thus making the wider view the more accurate view? I don't know, but I would be interested to find out. 

When I run, I usually tote along my Garmin Forerunner 405CX in order to keep track of the miles trod, and to capture the information into courses and routes for others to (potentially) follow if it turns out to be a good one. Since not everyone uses Garmin products and may not want to use the Garmin website's courses feature, I also convert the GPS data to Google Earth and post all the information into a .kmz file (scroll to the download link) for viewing in Google Earth on a local pc.

The data is the same: XML data containing latitude and longitude and that's about it. When it gets to either the Garmin website and/or Google Earth, that data is interpreted over maps to give the user a visual look of the data rather than lat/long coordinates, and gives distance, and elevation profile. This is where it gets all divergent.

I did a run last Friday that I converted to a course. The base run data as uploaded is shown below (Sorry, you don't get to see my imminent heart attack displayed in the heart rate info, nor the "trudge factor" in the timing chart.):

When I elected to save the run as a course, the data changed! Instead of being over 7 miles, the course data was 6.95, though the elevation data remained the same with a gain of 1066 feet. However, I do like that the elevation profile no longer starts at sea level, making the 1000+ elevation gain almost look like it hurt as much as it did.

In addition to saving the run as a course, I used the Garmin function to export the data to a Google Earth file. This conversion results in yet another divergent data set. In this case, the run distance shows as 7.05 miles, which isn't too terribly off (only 1 %) from the base run data, but a big delta shows up in the elevation gain: 1458 feet. Wow. That's a 37% difference! I must admit I much prefer the look of a Google Earth elevation profile over either Garmin:

Just looking at the elevation profiles, I get the feeling that Garmin is smoothing the data that erases the small changes in elevation despite using Google as the mapping base. However, over the course of a longer run, the tiny smoothing changes the overall run a lot. Those three and five foot elevation changes on the trail add up. Tell me. Toward the end of a run, any little hill up -- only to go back down -- gets a sound round of cursing from me.