GPS vs. GNSSPosted by not-my-real-name on January 10, 2020 at 1:38 pm
My GPS receiver is dual frequency. I use it for purely static data collection when possible to get geographic coordinates on my survey and for traversing a long line that I cannot form with a closed circuit.
In planning good conditions, the receiver will view 9 to 11 satellites through the two or four hours of data collection.
How much accuracy improvement could I expect if I included the GNSS constellation? Would it be a significant improvement?
Currently, I use OPUS to post process data so GPS is my only choice there.
- 17 Replies
- MemberJanuary 10, 2020 at 1:45 pm
I don’t think you will see much if any improvement in static results. The real benefit of multi constellation is in real time work (RTK/VRS), or precise point positioning (PPP).
- MemberJanuary 10, 2020 at 2:12 pm
John is right.
Post process static, out in the open, is still a quite viable mechanism.
But, rtk, and such, in the woods, is quite useful. The more constellations the better then.
- MemberJanuary 10, 2020 at 2:44 pm
If all you wish to do is get static results, GPS will be fine. I would suggest getting some type of processing software so you don’t need to rely on OPUS. You will have many more options to get work done if you can do it yourself.
- MemberJanuary 10, 2020 at 3:01 pm
For what you are doing the only real benefit of GNSS is that the additional satellites will shorten the static time you need. That might be of value if you get some jobs where you are only going to be on site for a couple of hours, or where sky visibility is restricted and it just happens that most of the GPS constellation is hidden. Such situations do arise – I’ve had occasions when most of the satellites were Glonass.
- MemberJanuary 10, 2020 at 3:05 pm
The more birds that are in use at your rover using Static allows for less occupation time for excellent results.
With 8 or 10 in view and in communication, a couple of minutes of occupation can yield the same quality as being there for hours. Canopy and a few other factors in there also for the desired occupation time.
Under canopy, I have had great results in 3min and then moved 50ft and the static session took 45min and at most around 2hrs and better results than what the local RTK guys have been accomplishing. In their defense, they are still learning the limitations of their operators and their equipment.
Still, it was less time than running thousands of feet clearing brush and shooting in with a TS.
- MemberJanuary 10, 2020 at 3:38 pm
Yes, you can never be certain how short a time will give a good answer. Two hours is around 95% certain of being hard to better (sensibly, unless you are counting the mm.) I’ve had spot on answers in 5 minutes (and rubbish ones in 90 minutes). If the job is that short I wonder why you would bother with it (unless it is paying stupid money) – on most sites I would expect to be there longer than an hour. One exception might be when it isn’t safe to leave the base unguarded, but on those sites you probably need an assistant to provide you with protection anyway and you could always do 10 minutes at the start of survey and 10 minutes just before you left site – on the same point obviously
- MemberJanuary 10, 2020 at 3:43 pm
To expand a bit, the rule of thumb doing static processing from the old days was 10 minutes plus 1 minute per mile.
This to me is a very conservative rule and probably very outdated.
From experience I can say that shorter times are very viable depending on your needs and your error budget.
Getting a point to .02′ instead of 2mm may mean little or nothing to you, but the time savings can be significant to your work flow and getting a processing engine will be a big step up instead of using only OPUS and the time constraints inherent using it.
- MemberJanuary 10, 2020 at 3:55 pm
OPUS remains GPS-only, so if you are only going to be using it for post-processing, adding a constellation will not help.
But if you are going to be using a commercial program in the future, adding at least GLONASS will help a lot. Count me among those who like having the flexibility of multiple constellations and the ability to shorten static sessions. A lot of folks disregard mission planning and end up paying for it – it sounds like you are already using mission planning, so you will be able to maximize productivity.
That being said, OPUS is free, and GPS-only receivers are very wallet-friendly…“…people will come to love their oppression, to adore the technologies that undo their capacities to think.” -Neil Postman
- MemberJanuary 10, 2020 at 8:21 pm
Hi, I already know that. Thank you. Also my occupations are strictly static and usually observed twice on different days. So, I’m not in a hurry.Historic Boundaries and Conservation Efforts
- MemberJanuary 11, 2020 at 5:04 pm
100% agreed with everyone else’s posts! If you get into RTK the difference is in my opinion is huge.
- MemberJanuary 12, 2020 at 5:17 pm
My experience has been that multiple constellations does help in post processed fast static. Not all static is performed in clear open skies.
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