Timing gate course discrepancy

> Following a non-optimal course line adds up mile by mile.  So the longer the course, the more off the total distance will be.

That was my point about cumulative GPS distance exactly. That's why I say that I see a relative 0.5 % error on a good day, as opposed to an absolute value of X km / miles.

However, the whole point of the course timing gates feature is that the software timing gates are placed at known locations corresponding to the "real" markers (in some cases there will actually be a real physical marker).

For example if there is a physical 10 km timing mat in a 21.1 km half marathon course, I would expect the corresponding 10 km software timing gate to be set at the same coordinates. When I pass the physical 10 km marker in a half marathon race (21.1 km), this means that I ran 10 km of the course. It doesn't mean that I ran 10 km exactly, or that my GPS device will measure 10 km.

If we can assume that every real physical mile/km marker is as accurate as possible, and that the organizers know where all the other markers are supposed to be (e.g. 2, 3, 4, etc and all the other markers that may show up on a map and not in physical form), then we can have the same confidence in software mile/km markers, keeping the following in mind:

- constant error inherent in actually setting a software marker to correspond with the known location of the "real" marker

- constant error inherent in determining your physical location via GPS

If you don't trust the determination of the physical course markers / course measurements in the first place, then ofc you won't trust software timing gates based on those measurements. In that case you won't trust that a 10 km race is 10 km, regardless of whether or not you run it with a Garmin watch or with the timing gates feature.

I think the entire point of the timing gates feature is to get rid of the cumulative relative error associated with GPS distance, at least for the purpose of timing / pacing / lap splits.

And I think it should be obvious that the software timing gates are set based on the known physical locations of the course markers (whether virtual or physical), not based on cumulative distance as measured in software. There is already a way to see mile/km markers in Connect based on software cumulative distance, without resorting to this new feature. That's not what the timing gate feature is about.

I guess that's where I'm confused.  Are timing gates places at known locations along the course (e.g. manual placement) or at positions calculated automatically based on the mapping software?  I was assuming the later.  Pretty sure that's true if I create my own route in Garmin.

mark.yarvis said:

Are timing gates places at known locations along the course (e.g. manual placement) or at positions calculated automatically based on the mapping software?  I was assuming the later.  Pretty sure that's true if I create my own route in Garmin.

Yes, the initial locations of the virtual timing gates / markers are determined by the corresponding course distance in Connect. i.e. The "1 km" timing gate is initially placed at exactly at a course distance of 1 km, and in general, the "X km" timing gate is initially placed at exactly at a course distance of X km.

But you are able to freely move any of the timing gate markers. As with all things Garmin, the ability to do so is not obvious, and the method to do so is not intuitive. (You are not the first person who missed out on the existence of this feature.)

In the Connect website:

- Open / create course

- Edit course (ofc you cannot enable auto lap by timing gates without pressing the Edit button, which is another thing that has confused some users)

- Enable auto lap by timing gates (this will add purple markers for every mile/km of the route)

- Click on a purple timing gate marker - this will change the sidebar to "Edit Course Point" mode. The sidebar will show the elevation and course distance for the course point. (Note that the course distance associated with the point is initially exactly the same as the nominal distance of the point.)

- Click anywhere on the course to move the marker (now the course distance of the point should be different than the nominal distance)

- Press Done to save your changes

So if I am looking at an "official" race course in Connect with timing gates, my assumption is always that the markers were manually moved to coincide with the "real" km/mile markers. (This can be verified by clicking on a timing gate and checking whether the course distance for the timing gate is different than the nominal distance of the course point. I would expect that some or all of the timing gates would have course distance different than nominal distance.)

Again, without the ability to place timing gates anywhere you want, the timing gate feature itself would be fairly redundant and useless (as you pointed out).

Maybe Garmin should implement some kind of interactive tutorial for auto lap by timing gates when you enable it for the first time.