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

[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.

[eub.livejournal.com]

Now I'm curious just how high an altitude GPS receivers (consumer, specialty, military) are programmed to solve for. Do they actually handle when their location is above the satellites? Just based on the precision of their ranging, it should be possible to distinguish between convexity and concavity of satellte 'shell' (obvs after they've acquired 4+ satellites). But if dropping that capability saved the designer a millisecond or a dime, I have to assume they'd shed one geeky tear and drop it instantly.

If they do support it, I hope they maintain test coverage. :)