two dimensions out of three

[cellio]

It's funny to see (well, hear) my phone's navigator app react to parking garages. "Do X... oh ok you're going north so do Y... oh you're going west so do Z... oh you're going south do A... oh you're going east do X which I'll pretend I haven't said before..." -- iterate until you reach the exit. It doesn't respond to elevation, only latitude/longitude.

I can think of three possible reasons for this, and I wonder which it is (or if it's something else I haven't thought of):

1. The GPS in the phone doesn't detect altitude.

2. The map data (Google's, in this case) doesn't record elevation. It does you no good to know that the GPS is at a certain elevation if the app can't tell that that's 200 feet above the road, after all.

3. The GPS and map data are available, but the app isn't programmed to take it into account. How often does this really come up, after all?

Comments

[browngirl.livejournal.com]

*reads, nodding contemplatively*
*gets to the cartoon*
*falls off bed laughing*

[eub.livejournal.com]

I suspect it's mostly (3) in play here. As a bug it's probably more silly than it is harmful or annoying?

GPS does inherently pick up altitude, but it's less accurate than location horizontally, i.e. the error ellipsoid is tall. Basically because you do not generally have satellites available near directly overhead and rarely straight downwards -- the constellation you see is pretty 'flat'. So when you triangulate position based on your approximate distance to the satellites, the vertical error is rather high, because of the geometry of the solution.

On top of that, seeing satellites from inside a parking structure is hard, so who knows if your GPS has any idea of your elevation when you're in there.

Originally map data didn't come with much elevation data at all, even relative. (You may recall the days of "turn left from Forbes Ave onto S Neville Way" directions from map sites.) It's fairly easy to paint your road lat/long data with elevation datasets derived from orbital radar ranging, but what that gets you is the *top* of your parking garage, or the trees covering the road, etc. Actual elevation of the roadbed has been a longer time coming. You can speculate that crowdsourced GPS data might be useful here.

[cafemusique.livejournal.com]

My impression, just looking at some of the tracks and profiles I've recorded with my phone is that the elevations reported by most phone GPS hardware are subject to a lot of error. Also, in a garage, there's an obstructed view of the satellites, so the accuracy is even lower. I am not sure that the GPS chips in phones are precise enough to determine what level of a multi-level structure one is on.

[anastasiav.livejournal.com]

The flip side of this (sorta) is that for many personal fitness devices (ie: FitBit et al) they will sometimes calculate that you're doing activity based on changes in elevation even when you're sitting in a car.

Thus, my friend drove up Mount Washington in a car and was "rewarded" by her fit bit for climbing 796 flights of stairs that day.

[sethcohen.livejournal.com]

I wasn't available to respond to this post when it was first published, but realized that I wanted to get back to it. Most of the cogent things I would have said have been said by others, but there's one more thing I wanted to point out.

Your phone will read the GPS signal and tell you your location based on the signal timing. The phones are only programmed to do so appropriately on the surface of this planet. They will tell you that you're in Pittsburgh (and where appropriately) even if your elevation is twice orbital distance (based on the orbit of the GPS satellites it's receiving signal from) above Pittsburgh.

I have the same problem when I'm in my parking garage at work. I've been coming from enough different routes long enough that now when I see work and get to a stop light, I exit my route so my phone doesn't bitch at me for three minutes as I climb floors in the garage.