Virtual Reference Station (VRS) for OptiSurface Landform

Graeme Cox explains use of VRS for OptiSurface landform.

Related article: Practical Test on Accuracy and Usability of Virtual Reference Station Method in Finland





Transcript


Hi, it's Graeme Cox here.  I've just had a client who's inquired about using a Virtual Reference Station or VRS for the correction signal to do ag earthworks or OptiSurface earthworks. They've inquired about the accuracy so I did a bit of research and found this paper from Finland.

VRS system is basically a network of base station spread out over a large area typically spaced about 70kms apart or similar. This is an example here of a network in Finland.  They're usually using the mobile network to send the correction to the earthmoving equipment. I'm concerned about that because we recommend a base station right beside the field for the highest accuracy. When you get the nearest base station will potentially be 35 kms away so I'm a bit concerned that the accuracy of this system would not be recommended for earthworks.  Remember we're pushing the accuracy limits of the GPS system when we're doing OptiSurface landforming. 

Here are some results that show the accuracy.  They basically took 2000 measurements all around that network and this is the type of accuracy results they got.  This is the northing error and this is the easting error.  And this is the vertical error as you can see it is worse as you'd expect.  Based from all of them you'd think 95% confidence is probably +/-75mm. 68% confidence which is often quoted as probably more around 35mm.

What's interesting in this paper is they also looked at the distance from the nearest reference station.


Figure 8. Connection between accuracy and distance to nearest reference station

This is the horizontal error and this is the vertical error. You can see the horizontal at 95% confidence which is the upper enveloper here, it does increase as you go over time although the average error here probably does increase that much but were talking at 95% confidence and it does increase.  Maybe will flatten a bit here somewhere which would make sense.

But what we're more interested in is the vertical error for earthmoving and you can see that when the base station is very close, we have a 95% confidence of around 25mm and then it increases quite rapidly for 12kms up towards 100mm for 95% confidence.  We halve that for 68% confidence or one standard deviation. 40mm halved equals 20mm and then 100mm halved equals 50mm.  Based on that, I wouldn't recommend VRS for doing OptiSurface type earthworks because that amount of error is quite significant.  That's why we like to have a base station right beside the field so then the base line will be about a kilometer away so we're operating down this region here.

OK. I hope that's useful. If you got any questions, just shoot an email to support@optisurface.com and we'll try to answer them.

General

  1. Virtual Reference Station (VRS) for OptiSurface Landform
  2. Accuracy of RTK and RTX GPS
  3. Export To Field Level .gps File From UTM Coordinate System
  4. How Often Does The Earthworks Need To Be Done?
  5. GPS Accuracy Affected by Solar Activities
  6. Is OptiSurface Compatible with John Deere?
  7. Is GPS Accurate Compared to Laser?
  8. Is Cellular RTK Networks Accurate Enough for GPS Landforming?
  9. Trimble FMX User Guide
  10. Effects of Topsoil Removal and Redistribution on Irrigated Crop Production
  11. OptiSurface Designer on Apple Computer
  12. Earthworks Conversion Chart (Metric to Imperial) & Planar/OptiSurface Comparison
  13. How to Check Your System Specification
  14. OptiSurface Designer and John Deere's APEX
  15. Designs Generated with OptiSurface Designer
  16. Legend Way Off Screen
  17. Computer Only Running at 30% of the CPU Capacity
  18. French Manual for OptiSurface Designer
  19. Introduction to OptiSurface Landforming
  20. Using the Lay of the Land to Let Water Drain From A Field
  21. The Benefits by Using OptiSurface Design Software
  22. Draining Surface Water Using OptiSurface Designer
  23. Difference Between OptiSurface Designer Software and the Trimble and Deere Solutions
  24. OptiSurface and Auto-steer GPS: Key to Cost-Effective Erosion Control
  25. 800ha OptiSurfaced for Lateral Move and Drip Irrigation
  26. The Disadvantage of Practicing Multiple Grade Designs
  27. Why You Don't Want Ditches in Your Field...
  28. Connecting Pot Holes to Drains
  29. Dongle Or Licensing System
  30. OptiSurface Designer System Requirements
  31. Hardware List Providing the Best Service and Getting the Most out of OptiSurface Designer
  32. Computer Operating Systems
  33. One or Two Scrapers
  34. Base Station Mobility
  35. Base Unit Distance with GPS Receivers On Scrappers
  36. Getting the Information to the GPS Units on the Scrapers in the Field
  37. Downloading Maps to the Equipment / Machine
  38. Implementing Designs for the Field
  39. What Machine Control Hardware is OptiSurface Designer Compatible With?
  40. Base Station and Line of Sight with the Scrapers
  41. One Base Station with Multiple Scrapers
  42. Training Topics
  43. Two Legends Visible
  44. Auto-Backup Files
  45. Speed Up the Display Graphics (eg Zooming and Panning)

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