How do I use differential correction with a Trimble GPS?
August 1, 2011 8:54 AM   Subscribe

Why can't I differentially correct some GPS data I collected with a Trimble GeoExplorer 2008?

Our support contract expired so perhaps I'll be able to get some help from the hive before I decide to pay for an expensive support phone call at some indeterminate point in the future.
I've collected various amounts of GPS data using a Trimble GeoExplorer 2008 running TerraSync 4.10 professional. It was my intention that once I got back into the office I'd be able to load up the collected files into Pathfinder Office and use the differential correction wizard to get a better accuracy along with a report of the point accuracy distribution.
Unfortunately, I've had no such luck. I'm fairly sure I'm running the tool correctly but have yet to get any results. I supply the data file and select a base station appropriate to my location to the tool. I start the processing but get this as a result, no matter the different permutations to settings or base station selection.

Finally, it's my understanding my data is fine as SuperCorrect data is always collected in the newest versions of Terrasync.
For the sake of clarity here's the output log.
Here's hoping someone has some esoteric knowledge of proprietary software.
posted by EsotericAlgorithm to Technology (7 answers total) 1 user marked this as a favorite
I'm not an expert (I know about things like GPS carrier phase and differential correction in theory, but haven't ever mucked around with a device capable of actually doing anything with it), but I'm seeing the "No carrier processing performed as file has no carrier data" message and wondering if your rover needed some sort of dwell time or something it didn't get in order to find the carrier sync, or if it wasn't recording in a mode where it was picking up the carrier phase?

(Seems kind of strange to me because I'd expect that you'd be able to do some basic correction for ionospheric delay even on the non-carrier sync'd data, but if your receiver's already doing much of that with comparisons of the L1 & L2 signals it may not matter. Again, my experience is just with cheap consumer devices.)
posted by straw at 9:27 AM on August 1, 2011

Response by poster: I was thinking something along those lines as well, but at the very least it seems that it should be able to do the code processing portion. I do think you're right about the dwell time (and possibly the mode) as well. If my understanding is correct it should be doing the L1 & L2 corrections in real-time along with SBAS. The unit does have the ability to be used as it's own base station so I think the carrier sync may be more applicable to that then when roving due to the longer time for syncing.

Thanks for the help, it's making me do the initial research again and clear some misconceptions. Trial by fire.
posted by EsotericAlgorithm at 9:52 AM on August 1, 2011

So I'm just browsing chapter 12 the GeoExplorer III docs ('cause it's the first relevant looking thing that came up when I googled "Trimble GeoExplorer 2008 carrier phase mode"), and it (and a few other documents) suggests that if you're in the right mode on your device, you'll be interacting with it to have a countdown timer that'll need to run from somewhere between 7 minutes to 45 minutes (if you've got clear line of site to 4 satellites simultaneously and everything works right).

If the 2008 model is like the III model, this suggests that the data you've collected is probably not correctable, and that you're gonna have to do some more interaction with the device.

tl;dr: Yep, you're beyond the limits of my practical expertise. Sorry.
posted by straw at 10:56 AM on August 1, 2011

Response by poster: Anything helps though. Apparently the model I'm using (GeoXT, should've mentioned) does the carrier collection automatically.
posted by EsotericAlgorithm at 11:44 AM on August 1, 2011

Best answer: What's the version of Pathfinder Office? v4.1 strips out the SuperCorrect data during the data transfer. v4.2 and higher is SuperCorrect-compatable or use the standalone Data Transfer tool.
posted by llin at 1:25 PM on August 1, 2011

Response by poster: So happy. I thought I'd tried updating the software but apparently the update in the menu doesn't update the version, just small incremental updates released by Trimble (intuitive...).

Vibrating with joy.

Thanks, I naively put a lot of hours into collecting data thinking post-processing wouldn't be a problem. If you're ever in Portland, Oregon I owe you a beer.
posted by EsotericAlgorithm at 2:47 PM on August 1, 2011

Glad to hear it worked out!

I'm in Portland a couple of times a year and a free root beer sounds great! ^_^
posted by llin at 11:23 AM on August 2, 2011

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