DGPS, or "You want <1m accuracy?"

Discussion about software such as GSAK, OziExplorer etc, as well as all things hardware, GPSrs, laptops, PDAs, paperless caching, cables etc
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Papa Bear_Left
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DGPS, or "You want <1m accuracy?"

Post by Papa Bear_Left » 17 September 04 11:56 am

Following on from another thread, these are my impressions of a Differential GPS over Internet Protocol service that's being trialled here in Christchurch:

It's really a commercial service that's meant to work with Wi-Fi connected, highly accurate fixed GPSrs like those made by Trimbles, but the provider offered to let geocachers beta-test it using whatever TCPIP connection they could. My post on the local forum:
Papa Bear_left, on gps.org.nz, wrote:I played a little with this at home, using a laptop with a serial connection to an eTrex and Wi-fi to the Net, and it worked but wasn't really useful (I already _know_ where I live!)

Then today I finally ironed out the problems I'd been having getting my old PII laptop to use IrDA to a Nokia 6310 and serial to the eTrex. I fixed it by realising that it _didn't work!_ and wasn't going to!

So, using my work laptop (IBM T41) with a USB>serial adaptor for the eTrex, I got it working in the backyard and went out to mark some waypoints for two new caches we've had waiting on this.

Abso-bloody-lutely brilliant!

One gz was a problem, as it was under trees and I could only ever get >15m EPE there, with any of our GPSrs. You can triangulate to find a point, but setting one that way is a pain!

Today, I sat there with the eTrex getting 4-5 satellites and about 20m EPE, down to about 12 occasionally. I dialled my ISP with the Nokia (just standard 9600 connection, not GPRS), connected to the server and watched as the "D"s appeared on the eTrex satellite display and the EPE dropped to 3m!

Other waypoints more out in the open went from a respectable 5-6m EPE down to 2m. And it was repeatable.

I tried the sign outside Trimbles (familiar spot, somehow...) and with 1m EPE (!) I matched the coords to .01 seconds. Good enough for geocaching...


Now, this is all a little cumbersome for finding caches, and it only works within a relatively short range of the base site, but it's great for accurately placing waypoints in suburban caches. It just gives more confidence that the coords are correct and reduces the size of the search area.

Next on the list is to try this using the Palm, with an IrDA link to the phone and a Bluetooth link to my Holuz GR230 GPS, if it supports DGPS.
Now, _that's_ almost worth using for a search occasionally...

It shouldn't be too expensive, as I could get a connection and a reading withing about 90 seconds once I had it figured out.

Thanks for letting me try this out, Flashkiwi; it's a buzz!
The "short range" turns out to be up to 400km, which is a long way in NZ, and even in Australia to anyone except maybe the Red Ochre guys!

The Trimbles sign I tested it at is the site of one of our caches.

I don't know what's on offer in Oz, but it's worth finding out!

i!, Is this on your "to do" list? :)

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