Robert answered this nicely. I will add a few things I have come to learn since we use both single baselines and VRS.
There are key differences to be aware of if traceability is a concern:
Single station RTK:
- Good for shorter distances from the base. Perhaps 5 miles or less, but you could stretch it a bit. The full PPM specs would apply, which is based on distance measured.
- It should be easy to find out from the base operator what coordinates are being broadcast based on the IP address and port.
VRS:
- Can go much further distance from any base, being that the PPM error is being cut in half, according to my understanding.
- “VRS” tells us that it is a “virtual” reference station. Even though it is measuring from just one of the stations in the network (random, but presumably the closest), the broadcast information is tweaked based on an entire network solution. (Don’t quote me on this, though, I'm still learning!)
- The VRS operator should be able to provide the coordinates and epoch of all stations.
Since traceability is important to us, whenever using VRS we do the following:
- Collect some static data onsite, enough to process to CORS or VRS data.
- Obtain the raw T02/T04 files from the VRS operator and process vectors to our data so we have a direct connection to things we know and understand. Maybe overkill, but I’m in southern California where we are moving at 0.13 feet per year!
- I don't completely rely on VRS coordinates without checking. It's like a black box to me.