|
Australia | A few points:
1) GPS scientists are able to model the tropospheric (lower atmosphere) delays in the GPS signal reasonably accurately which means a thunderstorm, which occurs in the troposphere, should not significantly affect CORS stations observations or network accuracy. Observations from low-elevation satellites are the most affected and are weeded out of the calculation by the receivers.
2) Modeling ionospheric (outer atmosphere) delays over time is much more difficult hence the ionospheric disturbances caused by solar storms mess up these models... and your accuracy. RTK technology is far more immune to solar storms than is L1 or 'floating' positions and you will find RTK CORS availability superior to WAAS, Starfire and Omnistar at the height of solar activity in 2011.
3) VRS does not "interpolate corrections". It creates a 'virtual reference station' (ie a mathematically created base station) near the GPS receiver on the tractor. This is why VRS is called "zero baseline" RTK in that there is theoretically no distance between the tractor and the base station. This is why worrying about the distance to your nearest base station in the CORS network is irrelevant if it has been designed properly. Let's hope professional surveyors in the DOT's can design properly... with Leica's help of course.
4) The reason why radio transmitters were originally used for GPS RTK datalinks is simply that they were available first. Cell data services have now caught up and are in many ways superior. This is becoming true for much of rural America. It has nothing to do with "staying within 8 or so miles of a single RTK base". Leica has had long range RTK (18 miles) from a single base since 2001, (Novatel now has 30 miles) which has been well outside ground level line-of-sight radio range for many years. Cell data simply helps fix a line-of-sight problem.
5) CDMA cell data services (1xRTT) are dedicated digital channels and are not shared with voice... by any carrier. You are thinking of the old analog network which is now dead.
6) Here are the design criteria for the Iowa DOT Network straight from their web site. Ask your local private network provider or someone with a single base station if they can guarantee this level of service.
- Statewide Coverage
- Accuracy (1 cm Hor.; 2 cm Vert.)
- Precision (2 Sigma)
- Open Architecture (RTCM 2.3, 3.0, 3.1, CMR, CMR+)
- Base Station Redundancy
- Server Redundancy
In short, Leica is building Iowa DOT a 1/2" accurate RTK network, that covers the entire state with that accuracy, and will always keep working even if a base station or a server goes down... and everyone must be able to use it. Same is true of MNDOT and so on.
7) I would agree and say three or more machines are probably cheaper to run off your own base station than on CORS only because of data plan costs. However, the future almost guarantees the trend of cheaper and cheaper cell data rates to continue. The other option is to plug a 900Mhz radio into your office internet connection which is connected to the DOT server and you can get the RTK messages totally free without cell plan costs. (but that's another complicated story for another day).
| |
|
Questions about Coors & cell phone differential service
