GPS Professionals

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Comment by Antonie Kruger on November 16, 2009 at 1:19pm

Hi Gary, agreed. If you look after the simple detail, the bigger things usually falls in place. Rod bubbles....what method do you use to check the adjustment of your rod bubbles?

Comment by Jim on November 16, 2009 at 11:21am

sounds like you are my kind of guy Gary. Simple is good. I use the GPS for most all of my setups. How long are sitting on a point to get it down to digestable readings?

Comment by Gary Breisch on November 16, 2009 at 10:42am

Yes - once you have a good control network with the static, you can come off of it and localize on it with checks to make sure you will have good RTK xyz points. With many years of experience have found that the bubbles and hardware needs to be checked and calibrated on all the equipment used to get the same or similar quality that I have witnessed with the Total Station. Cross checking the results is very important to verify the accuracies that you obtain. It is amazing that I get such good results from my cheap ProMark3 RTK system in open relatively small areas with RTK and the same with the static in large areas that may not be as open if I occupy them long enough to the that mileage range as mentioned below. By the way, I use pole tri-pods now and no need for trr-brackets and cumbersome and timely setup conventional tri-pods. I have to weigh down the legs in high winds with water jugs I carry in my survey vehicle. Multible use with the water in the bottles and can empty them to lighten my load if needed easily.

Comment by Jim on November 16, 2009 at 9:59am

It is very important to know your prime configuration from Data collector to data Link, Data stream, Datum, geode, Timing, design elevation as opposed to benchmarks etc.

Yes Bill seems to have taken off... I know this is a huge topic right now. Answers are not easy as each situation has so many variables. Manufacturing issues to Satellite data streams.

Comment by Bill Englert on November 16, 2009 at 8:30am

rrmonillace, You started a great thread.
-Bill-

Comment by Gary Breisch on November 15, 2009 at 9:44pm

I get vertical great with post processing and downloading the CORS data a day later to assign as the basis. I use the mileage meter on my base and make sure the range grows to over the distance between the Base and the CORS. On all Rover shots I make sure I am double the distance or more from the Base till I stop the Rover Session and move to the next point. I have checked in to existing, old, established, benchmarks within 0.02 feet consistently. Now for vertical, my ProMark3 RTK in the Survey mode with post processing with GNSS software that came with it and the local CORS I can rely on good vertical datums for all my Elevation Certificates now without having to go miles away to check into an old benchmark.

Comment by Jim on November 15, 2009 at 9:34pm

The GPS at this point is just not accurate enough and consistant enough for any type FINEvertical needs. It has its place don't get me wrong and with the many new radio signals this may change in coming years. For now it has it strengths but fine adjustments need to be done conventionally in my opinion. I use the OPUS points in fine situation with GPS and have great success. %hrs on a point can be costly if not approached correctly. I set up in the early Morning while I have other work to do, Recon the area or other tasks. While the Rover is crunchng data. Many factors come into play here. We have a 50 tower CORS Network in our State an it is very reliable. maintained by our DOT. Coupled with a good Data link to stream the Data can be huge. I use the Trimble R8 and I am confident only to 3/8" anything tighter than that I change to conventional.

Comment by Michael Elbert on November 15, 2009 at 3:20pm

rrmonilance,To make a level control network with the tolerance of +-20 mm you have to run a level loop between your GPS control points with a rigorous adjustment.Otherwise you are completely at The mercy of GDOP and the value of gravitational acceleration at your particular location

Comment by Antonie Kruger on November 15, 2009 at 1:07pm

rrmonillace, what is the tolerance of 'precise'? In my experience, if you are looking for anything better that 1cm vertically, you need to take out the digital level and put away the GPS, even if you do post processing with precise ephemeris of the SV's. I had the Leica guys at my office a while ago. They have a GPS product for monitoring that delivers good vertical results. I do not think it is an RTK system, though. My teams are not allowed to use GPS to place levels that require an accuracy of 20mm or less, even then you have to keep an eye on the VDOP.

Comment by Bill Englert on November 15, 2009 at 12:34pm

rrmonillace, I use Sokkia GPS eq. When I want to establish vertical controls, I do a 4 hr static collection at more than location, process the rinex file thru OPUS. I then add these points to my locaization file and use both horizontal and vertical. All other local points, I turn the vertical off. This may not be the best way but I know it has given me the best results when there isn't an established bench mark to work from.

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