Differential GPS

I think you have apples, apples, oranges there.
RTK means Real Time Kinematic. I'm pretty sure that is the same thing as Real Time Differential GPS.
Now, static post processed is altogether a different monkey.
Static post processed means 2 or more receivers are turned on, PASSIVELY recording satellite data. Then the data is Transfered to a computer, and special software "differences" the data, to obtain the vector. A vector is like a very precise slope distance, and bearing, between the 2 or more receivers.
With Rtk, it's happening in real time, via a radio link, or cell phone link.
Post processed static is usually a little more accurate.
GPS surveying is the "way of the future".
More data, faster.
And, it is funner, if you have a JAVAD!
(in my totally unbiased, and humble opinion!)

Nate The Surveyor, post: 358730, member: 291 wrote: I think you have apples, apples, oranges there.
RTK means Real Time Kinematic. I'm pretty sure that is the same thing as Real Time Differential GPS.
Now, static post processed is altogether a different monkey.
Static post processed means 2 or more receivers are turned on, PASSIVELY recording satellite data. Then the data is Transfered to a computer, and special software "differences" the data, to obtain the vector. A vector is like a very precise slope distance, and bearing, between the 2 or more receivers.
With Rtk, it's happening in real time, via a radio link, or cell phone link.
Post processed static is usually a little more accurate.
GPS surveying is the "way of the future".
More data, faster.
And, it is funner, if you have a JAVAD!
(in my totally unbiased, and humble opinion!)

Yea, I had a pretty good idea as to what static and RTK were (I use them at work often)
I just have an interview Tuesday and the job description mentioned differential GPS which is not a term i'd heard before.
Based off of some light research online it sounded very similar to RTK.
I just wanted to clarify the difference.

It is possible they are referring to two different observables, i.e. a positioning solution derived from the GPS carrier wave (as in RTK & PPS) and from the code signal (as in stand alone but also, typically at sea, differential coded signals). This latter technique is a relative technique (as are RTK & PPS) but doesn't achieve the centimetric accuracy of RTK or PPS. Using the coded signal, it is more robust, works at longer ranges (if your data link is on a suitable frequency) and may achieve anything from +-5m to +-0.5m in plan. One may not choose to use it as a 3D system (height would be 1.5*poorer) but typically use the water surface to derive the vertical value.

I tend to believe that the term Differential GPS is an umbrella term for both static and RTK as they are both forms of using differential GPS.

Strictly speaking all three techniques are differential GPS as they are all deriving a position relative to another base station (or base station network)
The correction stream on what is commonly called Differential GPS (DGPS) is delivered from the SBAS satellites and gives approximately 1m accuracy. Need a paid subscription generally I think, but this is cheaper than a RTK quality subsciption.

1. phase differential real time = RTK = 1cm accurasy
2. code differential real time = DGPS = may be a foot in best case and down accurate
3. static phase differential = not real time* = 5mm and down accurate

*- each receiver data are recorded in internal memory, later on downloaded and postprocessd, you need to postprocess data from two receivers to get cm level accuracy.

As others have stated it's an umbrella term that I've heard for GPS that incorporates multiple units working together. At least that's what I've always assumed.

There are some techniques that use GPS in concert with differential levels, but I don't think that's what you are asking......

Actually it's old terminology IMO.

Then the data is Transfered to a computer, and special software differences the data, to obtain the vector. A vector is like a very precise slope distance, and bearing, between the 2 or more receivers.
[/quote wrote:

we have to keep in mind, though, what a dgps vector truly is: it is an inverse, based in indirect measurement(s), from two solved coordinates

Assume a firm wants reference checks without doing everything twice. You can set up for RTK, set a reference base or if nearby a CORS. After RTK in the field you can post process your stored rover file against the other base. It is time in the office versus time in the field.

Do not be afraid to explain your understanding of GPS terms and asking for a clarification of how they are using the terms.

I believe Leica for a while emphasized using a robot rod with GPS in conjunction with the robot for rather precise surveying.

Paul in PA

A little googling.....

Differential GPS in a general sense is just what we have all been doing with our stuff for years. A fixed base and a rover measuring the difference in position between the two.

DGPS in a marketing sense probably refers to the use of correctors broadcast by the Coast Guard to users with posiitoning needs less precise than surveyors but better than autonomous (eg/GIS, trucking, shipping). See this website.

Back in the day, DGPS was mostly for ship navigation, your GPS onboard received corrections, (probably just L1 and code-only) via a shortwave broadcast at around 400khz (just below AM radio). Seems like around 2007 whoever was running the differential broadcast system (Coast Guard?) turned it off in favor of more modern developments. Some of the older Garmins had a DGPS receiver accessory for getting those corrections. For fun a few times I have hooked my Garmin to a laptop via serial cable and used GNSS Internet Radio to get DGPS corrections from our favorite VRS network.

The SBAS (or USA, WAAS; Europe, EGNOS) corrections may be free but your receiver must be SBAS-enabled.
We have our own Trimble Base Station and there's a CORS nearby. We use the latter for Post-processed Static (PPS) and our own corrections broadcast on 450MHz for one or both of RTK and differential pseudo-ranges. Others (in UK, the Maritime and Coastguard Agency) broadcast dGPScorrections at around 300kHz (and I think that may be similar elsewhere). Other commercial providers used to generate corrections on other frequencies but perhaps they're superceded by Wide Area GPS via communication satellites.

The terms we use to describe our technology leave a lot to be desired. If someone says differential GPS it depends on the context. If it is related to surveying then in my opinion it would be cm level positioning using a rover and a base station.

About 20-15 years ago (from before SA was turned off until WAAS became popular) I owned a Garmin DGPS beacon receiver with an H-field antenna. I installed it in my old Saturn wagon to make the navigation receiver considerably more accurate. The nearest beacon was about 30 miles away on Point Loma in San Diego. It worked quite well for meter or so level positioning. With the advent of WAAS I threw it out. You can still find people selling Trimble "BOB" (Beacon On a Belt) receivers on Ebay for outrageous sums of money. That's what comes to my mind when you mention DGPS or differential GPS. Note that some modern survey grade GPS receivers can still output the old RTCM DGPS messages in addition to the newer RTCM RTK messages.