Elevation Correction

by pkan

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1.9

Updated:

Nov 29, 2017

Idea for elevation correction

Idea for elevation correction

Postby pauljhodgson » Fri Jul 22, 2011 9:22 am

Hi,

I'm new to the forum (although I have been using ST for some time) but I have an idea regarding elevation (actually grade) correction that I thought you might be interested. I am not a programmer myself so I thought I'd pass it on.

Many of us cycle with both GPS and a speed sensor on the wheel at the same time. Theoretically, at least, it should be possible to determine the slope at any point using the data from both. I don't know how this plugin works already (it may work on a similar concept but I was under the impression it used a database) so this system may already be how it works as it is actually possible to measure grade purely from GPS, however, GPS is notoriously inaccurate when it comes to height. Anyway, the speed sensor on the wheel measures exactly how far the wheel has moved. From the GPS co-ordinates, you can determine the HORIZONTAL distance travelled along the Earth's surface (I think the distance GPS gives actually corrects for slope as it works in 3D space). From the ratio of these two distances, you can determine the grade of the slope. For example, at 30% (very steep I know, but it illustrates the point), a calculated horizontal distance from the GPS co-ordinates giving a distance of 10m would be matched with a distance measured by the wheel sensor of 11.55m.

One limitation is that the above only tells you the grade and unfortunately not whether you are going up or down hill! I'm sure there is another way of finding this out (from database, or any other method that tells you elevation). The advantage is that it would give very localised gradient.

Hope this is useful,

Paul
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Re: Idea for elevation correction

Postby pkan » Mon Aug 01, 2011 3:43 pm

This would only work for very steep slopes. For a 5% slope, which is quite steep, 50 m in elevation per km, the ratio will be 1.001, corresponding to a difference of only 1 m per km. The GPS horizontal distance error is probably larger than that.
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