Although I do not own a RTK gps, I follow all messages about this type of equipment. The most intriguing aspect to me is the use of a single unit a cellular telephone and a local area network.

In one of the posts, I read about the use of data from local CORS stations.

My questions are:
Do all CORS transmit the corrections?
How can a person get the data?
Do you need a license?
Is the data free?

Not all CORS transmit RTK corrections, some only provide RINEX data for post-processing.

Many RTN's (real-time networks) are either via DirectIP (IP address and port number) or NTRIP connections (username and password assigned by network administrator). The person wanting to receive corrections would need a GPS/GNSS receiver, internal or external cell phone modem and data plan from a cellular provider, data collector and data collection software that supports DirectIP or NTRIP corrections.

No need for a license, at least in the US. Although it is absolutely necessary to get proper training on what you are getting yourself into when utilizing a RTN for RTK or post-processed corrections.

Some RTN's are open and free to the public. For example, the Iowa Department of Transportation, just designed and implemented a state-wide SpiderNet RTN and it is free to the public. Sign up on the internet, you are assigned a username, password and the necessary IP addresses and port number are provided and then you are set as long as you have the needed hardware and software. There are also many privately held networks by local GPS vendors. For example, in the Chicago, Illinois area there are two GPS vendors that have RTN's established and charge a nominal fee either on a monthly or yearly basis.

I hope this helps.

Brett

You can also set up an office base station like a CORS with a PM3 and have it broadcast corrections over the internet - it takes a little work but it works well. You can calc the coordinates with static observations then use the position from there on. I also set a couple of concrete monuments within a couple hundred feet of the office so I can verify everything is working as expected before I venture off. till now I used radios, then set the office base station for static, and now I have been setting up the "office cors" station. All with two PM3's (RTK capable) and a cell phone. I still use the radios at times - I get about 2 plus miles in subdivision and town areas with the radios and of course they move with me to any site.

The (office cors) PM3 base station can even be converted to a "mobile" or portable cors type of station with a little more work. with the PM3 base cors Expect 10 plus miles RTK radius from the PM3 cors station wherever it is for very good results (with the single frequency PM3) and a little farther for approx (a tenth or two) RTK.

Phil has had some great results at much greater distances. Of course you can always bring a point into the site then RTK from there. If you want to spend nearly three times as much you can go with dual frequency RTK units to cors sites and networks which will include yearly subscriptions ($1200 plus a year around here) unless someone is providing that for free as mentioned in the above post. The dual frequency units will usually go a radius of 30 miles or so easily. I think in time more "goverment" or "dot" agencies will be providing this service. Locally here they sub it out, or rely on private contractors so far in several areas so you have to buy their subscription service.

Ken

I can have access to a private network that has stations distributed in such a way that I would never be more than 10 miles from one of them.

I wonder if a PM3 would be reliable under such conditions, or should I go L1/L2.

I would try to limit your baselines to 10km, but I have heard of people getting a fixed solution at 10-12 miles with the ProMark 3 RTK. I would imagine it would take a longer to initialize (several minutes?) at that distance. L1/L2 would initialize in a matter of seconds.