Flutterby™! : GPS accuracy 2004-12-28 04:34:16.885153+00

GPS accuracy

2004-12-28 04:34:16.885153+00 by Dan Lyke 6 comments

I followed a link from /. about some guys who are trying to figure out how to land a "wing suit" (for those of you not up on skydiving, some background on the wing suit). What bothered me about this was:

The two were able to gather data using GPS systems attached to Luigi that tracked exact forward speeds, exact fall rate and glide angles needed for a safe landing.

I believe that landing a wing suit involves forcing a whip stall from a fairly high speed, probably over a hundred miles an hour, and getting to that point involves some pretty accurate tradeoffs of altitude and horizontal speed. GPS accuracy is 95% of samples within ten meters or so. I've never cratered from 30+ feet, but I've limped for quite a while after hitting ground from lower.

Anyone else see a problem here?

But this isn't the only place that people are depending on GPS when they probably shouldn't be. I've been told that I've got a relative who uses it to find a river mouth in surf when he's fogged in, riding the dory in from fishing through a relatively narrow inlet. Sure, he hasn't had a problem yet, but...

I worry a bit, but then I tend to be something of throwback when it comes to trusting my life to technology.

#Comment Re: made: 2004-12-28 09:11:19.572921+00 by: mvandewettering

I suspect we see a future Darwin Award Winner in the making. My take on it is basically the same as yours: it requires a carefully calculated stall maneuver that happens to coincide with the ground. Make a mistake, and you are a pancake. I certainly wouldn't insure anyone trying it.

Regarding GPS, a GPS by itself is a pretty poor altitude indicator, but there are certainly models which have integrated barometric altimeters. This could merely be a case of bad reporting rather than gross incompetence. But it's still lunacy.

#Comment Re: made: 2004-12-28 13:18:04.093443+00 by: meuon [edit history]

Dan, people that truly understand technology are loath to depend on it or trust it.

I did a little more reading... while watching a server do some maintenance. Looks like they were just using the GPS for data acquisition so they could simulate some things in a controlled environment using that data. When it comes to actually DOING it, the GPS may be a recorder of the event, but not a control method. - And they are redefining 'guts' as well as 'stupidity'.

Yeah, I actually didn't figure that they'd be using the GPS for the real descent, just for, in essence, simulating altitude so that they have a feel for where and when they're virtually landing.

Aaand, I remembered that, yes, as Mark points out, altitude is far less accurate than 10 meters using GPS.

They are probably capturing data for land "approaches" simulated well above the ground to see what it takes to get the stall right. As far as the guy becoming a pancake, he's a BASE jumper. He's used to working very close to the ground.

And as far as using GPS for boat guidance, is your uncle using RTK or some other corrected positioning system? There are a number of different systems for coastal navigation that correct the inaccuracies in GPS.

On my uncle: My impression was that it's just a cheap basic hand-held device. And maybe it's just been consistently good enough that he's never had a problem.