Hey guys
What are people using DGPS generally for?
And what is the difference between RTK and PPK in terms of the accuracy methods and how the system works
Any help would be great
Thanks again
Mat
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thanks guys for all you expert knowlede:)
If use DGPS - in this case you will use only CODE information. If you use RTK in this case you use CODE and Phase information from satellite.
PPK is mean post processing kinematic.
Precision:
DGPS - if use CORS network 0.5 m - 1 m
DGPS - if not use CORS network 5-10 m
RTK - if use CORS network VRS mod 1 - 1.5 sm, FKP mod - 2 cm, iMac or Mac mod 2 cm
PPK - in this case you must use base station accuracy abaout 2 cm.
lsl
Hi Mat,
Given the nature of this site, I'm assuming you're trying to do high precision work where 2-3cm accuracy requirements are the norm. If you're only looking for 1-2 meter accuracy requirements then PPK becomes viable.
Fundamentally the difference is how the solution is arrived.Do you understand that in both cases you are attempting to provide a solution at a remote point from a know one? To put it VERY simply the base station has a known coordinate and the 'wiggles' of GPS from the varied sources are modeled out at the rover.
RTK (Real Time Kinematic) is the field work where your rover is actively receiving corrections from a base station giving you, theoretically, something that could be verified with an optical instrument if the distances were not too far. Under RTK work, if there is something the negatively impacts the show you might catch it before tearing down. The GPS signal is really butchered under pine trees so I've seen shots take 10 minutes plus if there's any wind where the same shot taken in open terrain would take 30 seconds.
PPK (Post Processed Kinematic) on the other hand is where there is no direct connectivity between the base and the rover. You collect the two data sets and then bring things back together in the office and hope you were on the point with the rover long enough. In most cases bring the rover bipod because it's not blow and go. With our Trimble gear my usual workflow is to start the point measuring-> wait 8 minutes for the rover to collect enough data to change from a float to fixed solution-> shoot points a minimum of 3 minutes each (reason for bipod). If you're good enough to not go under any obstructions then you don't have to reinitialize. If you loose GPS lock for any reason then start over with the 8 minute init. I've been told anecdotally that one person was doing rough road centerline collection via PPK and tried to figure out if enough speed would hold GPS lock. Going under a single railroad overpass still brock lock at 120mph so he stopped trying. Once you're back in the office then the PPK base and rover data are combined in your office processing software and the magic buttons pressed.
As for accuracy - your mileage will vary with all the usual culprits that stomp on GPS data collection plus additional items just to make it a little more fun. ;-)
Bottom line - give the choice between RTK and PPK availability in similar situations I would choose RTK every time. PPK has too many variables that will put you back out in the field.
Hope this helps
Tom
GPS was invented to give military personnel accurate positions with 8-9m precision.
Like most measurement tools, GPS benefits from using offset or differences from nearby reference points to increase precision. These differential methods are generically called DGPS.
Conceptually, it may be as simple as knowing the error of position of a receiver working at a known location and subtracting those errors of result from another one at an unknown place.
Scientists, using very sophisticated interferometric techniques, developed the means to use the much smaller carrier waves to make measurements instead of the designed coded messages. When successful the results may be precise to a few centimetres or better. Some call this DGPS but most will call it carrier phase or survey-grade.
Again generally, DGPS is useful for mapping and some navigating with precision from sub-metre to a few.
Carrier phase GPS may provide real-time positions of a few centimetres.
Long-term post-processed carrier phase GPS may provide sub-centimetre results.
GNSS is a term meaning global navigation satellite systems and includes GPS.
JAC
Take a look at all of the discussions videos and tutorials on DGPS ...