hile, GPS geeks! to me!

[topaz]

At work we are exploring the possibility of using reverse geocoding to identify a VoIP user's location for 911 calls: we get their GPS coordinates, look them up in a GIS server and figure out which street address they're at.

There are a few sites which allow reverse geocoding lookups over the Web, mostly on a free-trial basis for evaluating someone's pricey GIS server software. I'm using these to determine how accurately we can get a user's fix. For that, I need data. And that, dear reader and owner of a handheld GPS device, is where you come in.

I need to collect a bunch of street addresses and the latitude/longitude that a GPS receiver reports at each of those locations. On this side I can do the reverse lookup and see how closely it matches your actual address. The more far-flung the locations, the better, as long as they're in the 50 U.S. states. (I'm not sure if we're required to provide 911 service in Puerto Rico or Guam.) I will be happy to tell you the results I get, if that makes it more appealing. :-)

If you'd like to help, please feel free either to post the results here or mail them to twp@rnktel.com, whatever you prefer :-)

Comments

[tfarrell.livejournal.com]

My experience with several handheld GPS devices over some years is that at present, you can reasonably expect to get a reading within about 50 feet of the actual location. However, once in a while odd glitches have made it read about 500 feet wrong for as much as 10 or 20 seconds. So, best to take a number of readings over time, discard any wild anomolies, and average the results.

Note however that I said you can reasonably expect accuracy within 50 feet or so... in Somerville, there are probably 6 or 8 homes within 50 feet of my front door. So, it's not very useful for dense neighborhoods.

[qwrrty.livejournal.com]

Right, these are exactly the concerns I have. Which is why I want to collect data: to determine quantitatively just how accurate we can expect the results to be. Which I didn't get. Oh well. :-)

[tfarrell.livejournal.com]

The problem is, the accuracy is variable. It depends on factors such as the individual receiver type, the type of antenna hooked up to it, cloud cover, precipitation, how tall the surrounding buildings are and how close together they are, how many trees are nearby and how close together they are...

You could probably come up with a quantitative average accuracy, but it would be meaningless in terms of individual cases.