I've read a number of articles on RTK GPS. I'm only familiar with using RTK GPS with an RTK Base Station, and I understand how the corrections can be broadcast to a rover. When would you use RTK GPS without using a base station, and is this practical?
[GIS] RTK without RTK Base Station
gps
Related Solutions
To go back to the basics of GPS positioning, you need to know the distance between the receiver antenna and each of the satellites the receiver is tracking. You need a minimum of 4 satellites to determine your position.
The distance antenna-satellite is equal to a number of full wavelengths plus a partial wavelength.
The receiver can only measure the last wave, or actually the partial wavelength.
The ambiguity is the number of full wavelengths separating the antenna from the satellite. So resolving the ambiguity is determining the number of full wavelengths.
Question 1. Will an RTK base station still provide accurate (within a few cm) data collection if the area in question is not very flat?
Answer 1: Yes it will, provided you follow necessary procedures to ensure your signals are not interfered with.The top/ recognized brands all guarantee top accurate and precise results in the most rugged of conditions.
Question 2. Do certain brands of RTK base stations perform better than others or are they all about on par?
Answer 2: In some cases yes, however, more often than not the differential is very marginal, a very well known and highly rated manufacturer is Topcon-Sokkia, I have yet to read a bad review on them.
Question 3. Are there any features I should specifically be looking for/avoiding in a base station set-up?
Answer 3: If I were you I would review instructional text on the setting up of RTK base stations, here are a couple I find very informative. 1.http://www.trimble.com/EC_ReceiverHelp/v4.15/en/SetupGuidelines_BaseStationOpGuidelines.htm
- http://web.gps.caltech.edu/classes/ge111/Docs/RTKGPS_Setup.doc (downloadable MS word doc)
Question 4. Are there other options for high-accuracy data collection that would work equally well/better than a base station/GNSS receiver in my situation?
Answer 4: I am a big fan of using base station/GNSS receivers I truly believe that there is no match in how effective they are. I would just look into the available types of GNSS receivers out there and decide which works better for you. http://www.navipedia.net/index.php/Receiver_Types
Here is just some general insight into RTK systems: http://www.navipedia.net/index.php/RTK_Systems
Best Answer
In all cases, L-code receivers need to resolve the "integer ambiguity" between signals received from the observable satellites in order to achieve their differential GPS accuracies.
So, I believe there are two questions you may be asking: 1) How can I achieve differential GPS accuracy using a single roving L-band receiver? or 2) How can I get the most out of an RTK receiver in autonomous mode?
For question 1: Alternatives to a "traditional" base station include subscribing to a virtual reference station network. -- these subscription services deliver real-time correction parameters over cellular-IP addresses.
Receivers download them and apply the differential corrections on-the-fly during RTK observations just as though they were receiving a signal from a dedicated base on a known point.
Question alternative 2 is less beneficial as autonomous L-band positioning is only slightly more accurate than C-code autonomous positioning. The better option to get full value from a single L-band receiver is PPK (post-processed Kinematic) where multiple autonomous surveys can be bundle-adjusted together with known baselines to reduce uncertainties and obtain RTK accuracy.
NOTICE that nowhere did I address any issue of "precision" because that is a non-issue when comparing multiple methods using a single device -- the precision is constant (and assumed to be arbitrarily "precise-enough".)
Bottom line, the satellite constellation, atmosphere, and correction baselines will dominate the solution accuracy and the precision is device-dependent.