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Thread: Any RTK-GPS surveyors out there?
05-10-2007, 12:36 PM #1
Any RTK-GPS surveyors out there?
I have a question that I won't bore the rest of the board with. PM me please."A local is just a dirtbag who can't get his shit together enough to travel."
- Owl Chapman
05-10-2007, 01:42 PM #2
No, no, this could be good for us GPS geeks.
I have accounts that sell RTK solution and know where I could find you help prolly. What stuff are you using, equipment and software and why the hell are you not running it on our handheld!!!!!
Lemme know or gmail at buzzron commie"boobs just make the world better really" - Woodsy
05-11-2007, 07:05 AM #3
As you wish, Ron. But I warned ya
We run an Ashtech Z-Xtreme receiver in RTK mode and output a NMEA GGA string from the receiver to other instruments/software (that require GGA input). Unfortunately, the Z-Xtreme receiver uses a very coarse internal elevation model (OSU91A), since most companies assume that one is using a data collector with an updated geoid model to receive, process (in terms of changing ellipsoidal elevations to geoidal), and store data in real time.
We are NOT using a data collector during this process, since we need the positioning/elevation data to be fed into a different system which multiplexes the GPS data (from the GGA string) with other data (bathymetric soundings) and then telemeters it to a laptop. The problem is, our resulting geoided elevation data is very bad due to the coarseness of the OSU91A model, which compromises our data.
We can (and have) determined a local separation between OSU91A and a different geoid (i.e., GEOID03) and created a systematic offset for each individual study area for later post processing of the data. But I'd like to avoid this and deal with "real time" corrected data, if at all possible (the whole reason behind using an RTK system anyway, right?).
I was wondering if there is a way to configure the receiver, or do something, that would allow us to output a GGA string from the receiver that uses a much more precise elevation model (such as GEOID99 or 03), not the coarse OSU91A? According to Ashtech, no firmware upgrade is available for the Z-Xtreme that would upgrade the internal GEOID model - and in fact this is due again to most companies assuming one is using, and storing data with, a data collector.
Some solutions I am thinking might be feasible:
1) use some kind of customized firmware to upgrade the internal geoid model of the Ashtech Z-Xtreme receiver (thus overriding the OSU91A) so that the output GGA string uses a much better geoid model - I don't think this is possible, at least according to Ashtech.
2) Introduce an intermediary step into this process - I was thinking possibly in the form of an inexpensive pocket PC or data collector that can run software that has the ability to take in RTK GPS data in from the receiver, but instead of processing and storing (like most end-point collectors do), process the data with a precise elevation model (GEOID03), and then output a corrected GGA string from the serial port which then goes to our other instruments, gets multiplexed, and telemetered for storage? It seems like most collectors are just that - end points that store data, not intermediate points that process and spit out data from the other end.
3) Avoid the above, collect all our data as usual, and then collect additional survey data to determine the exact systematic offset between the different geoid models (OSU91A and GEOID03) for each study area and post-process the data - like we've been doing. Takes more time, but might just be the way to do it."A local is just a dirtbag who can't get his shit together enough to travel."
- Owl Chapman
05-11-2007, 10:13 AM #4
lost me, I just use a model in the TSC 1. What do the guys at POB say?off your knees Louie
05-11-2007, 10:34 AM #5
They recommend to just do #3 (just suck it up and post process), or look further into option #2 and find what data collectors (and associated software) will allow a corrected NMEA output through a serial port so the GGA positioning string can continue on to be tagged with depth soundings, then sent to shore via radio modems. Expensive, but it might be my only option.
I'm hoping to find a cheaper pocket PC type thing that will run good RTK GPS software (Trimble's TerraSync?) and has the capability for input and output from standard 9 pin RS232s, and be cheaper than the traditional $3K handheld loggers."A local is just a dirtbag who can't get his shit together enough to travel."
- Owl Chapman
05-11-2007, 03:20 PM #6
As for the question, my brains melted out my ears. BUT, I will forward your question to a few people I know and see what they have to say.
Post processing sucks."boobs just make the world better really" - Woodsy
05-12-2007, 08:39 PM #7
Thanks Ron - this might do the trick; I will look into this product. Do you guys sell it?
Hope the knee is coming along!!!"A local is just a dirtbag who can't get his shit together enough to travel."
- Owl Chapman
05-14-2007, 01:14 PM #8
Yep, I sell em. www.junipersys.com. Archer Field PC.
PM me an email addy you want some blantant spam and pricing to come to and I will."boobs just make the world better really" - Woodsy
05-14-2007, 01:58 PM #9
By having a realtime computation introduced, you're adding one more step for things to go wrong in the field and unless you're recording your data at each process step you'll be unable to fix it if there turns out to be a problem with it.
I find it hard to believe that any company producing RTK equipment hasn't provided for the updata of the geoid. But if you can update the geoid, I'd do that and then the problem is solved (ie solution #1)."if the city is visibly one of humankind's greatest achievements, its uncontrolled evolution also can lead to desecration of both nature and the human spirit."
-- Melvin G. Marcus 1979
05-15-2007, 10:30 AM #10"A local is just a dirtbag who can't get his shit together enough to travel."
- Owl Chapman