There has been a rule-of-thumb that beyond about 15 or 20 km the single base RTK method would degrade due to the non-modeled effects of the atmosphere.?ÿ
Of course I have occasionally stretched that out a bit when necessary, but always tried to adhere to that.?ÿ
Monday and today I did an experiment, occupied 4 new points we just set and used a base about 50 km away. (observed control, 3 minutes, 180 epochs). Used GPS, GLONASS, GALILEO. The base was also using Beidou, the survey style in the rover was set to use it, but not sure why the rover didn't.?ÿ
Here are the differences (in meters):
| GPSID | Delta N | Delta E | Delta Horiz | Delta Up |
| 20009A | ?ÿ | ?ÿ | ?ÿ | ?ÿ |
| 20009A | 0.011 | 0.003 | -0.021 | 0.011 |
| 20009B | ?ÿ | ?ÿ | ?ÿ | ?ÿ |
| 20009B | 0.015 | 0.003 | 0.014 | 0.015 |
| 20009C | ?ÿ | ?ÿ | ?ÿ | ?ÿ |
| 20009C | -0.002 | 0.007 | 0.009 | -0.002 |
| 20009D | ?ÿ | ?ÿ | ?ÿ | ?ÿ |
| 20009D | -0.008 | 0.004 | -0.019 |
-0.008 ?ÿ |
These are differences from one day to the next (i.e. repeatability). Occupations were at different times of day. We are going to static survey the mons in the next week or two, and then I will compare the long static sessions to the RTK.?ÿ
Time for a new rule-of-thumb? When I get a chance I am going to try some longer lines, maybe 100 km next.?ÿ
Sweet, looking forward to the Static v. RTK comparisons.
🙂
Are you using an internet connection to go that far??ÿ It seems to far for a radio link.
John,
We have had a RTK base at our office since 2001 -?ÿ GPS and 10 miles w good sv configuration, then w/Glonass 10 miles on an ok day.?ÿ Fast forward today and Galileo's signals plus GPS L5 have allowed us to do much more with single baseline RTK.?ÿ Not sure how far we can with what repeatable accuracy we can go but with BDS coming into view who knows.?ÿ The old 8 mm plus 1 ppm worked well for 6 sv's and 12 signals but maybe not for 22 sv's and 50+ signals.?ÿ We are still testing.
Thank you for posting.
Some of your Delta Horiz.?ÿ don't look correct, especially for 20009A
Interesting! What time of day were they measured on both days? What was the troposphere weather like on both days. ?ÿ
Today we took our annual trip to a calibration baseline (Culver-Davies) over in Ohio. While there, I did two RTK observations, a VRS observation (ODOT) and also a realtime RTX observation.?ÿ
The two RTK observations were at 15:17 UTC (11:17 local) and 16:39 UTC. The baseline length was 217 km.?ÿ
Delta N: -0.023 m
Delta E: +0.042 m
Delta UP: +0.025 m
?ÿThe first occupation took a minute or so to initialize.?ÿ
Next, I wanted to compare it against an RTX observation (180 epochs). The base coordinate was ITRF2014 epoch 2020.1973 (i.e. current epoch)
The RTX coordinate from the realtime RTX at the CBL was ITRF2008 epoch 2005.0. So I used HTDP to convert the epoch 2005.0 coordinate to the ITRF2014 current epoch.?ÿ
Horizontal difference: 0.047 m
Azimuth 21?ø
Delta H: -0.058 m?ÿ
So that is about 0.2 ppm for the RTK versus the RTX PPP.?ÿ?ÿ
Even though I had Beidou enabled at both ends, and was using CMRx, Beidou was not used, not sure why not. GPS, Glonass, and Galileo were used. 18 to 19 SV's.?ÿ
I also transformed the ODOT VRS NAD83(2011) epoch 2010.0 coordinate to ITRF14 epoch 2020.1973, and compared against the average of the two RTK vectors (217 km):
Delta N: +0.028 m
Delta E: -0.027 m
Delta UP: -0.152 m (not sure what is going on with the height, should be better than that)
?ÿ
Pines to the south probably didn't help...
And the reservoir embankment to the north...
@john-hamilton thanks and wondering what the theoretical limits of single base line are. I know it is relative to the number of sv's common to base and rover. Agree the old ppm is out the door.
I thought I answered this yesterday, but I don't see it...yes, I apparently made a mistake in the horiz diff, which should have been
HD=sqrt(DN^2+DE^2)
I didn't save the spreadsheet, so I don't know what my mistake was. But DN and DE and DU are correct.
I consider the capability to go much further than before a good backup in case something goes wrong with a local base and I need just one more shot...?ÿ