AETC (Louisville, Kentucky) February, GNSS-Based Auto-Guidance Accuracy Testing Viacheslav I. Adamchuk Biological Systems Engineering University of Nebraska-Lincoln Background Auto-guidance (auto-steering) systems provide numerous benefits Performance of different systems depends on internal and external factors Quality of auto-guidance performance must be quantified in repeatable manner ASABE has two active projects: GPS Dynamic Test Standard (X) Auto-Guidance Test Standard (X) Outline Why do auto-guidance systems perform differently? What is guidance error? auto-guidance field day demo review pilot test of different systems using Nebraska Tractor Test Laboratory s test track What discussion items should be addressed in the future? Agricultural Vehicle Guidance Reference method Local triangulation Crop-based methods Mechanical feelers Laser row tracking Machine vision GNSS-based guidance Level of assistance Navigation aids Lightbar parallel tracking Auto-guidance Auto-steering Autonomous vehicles Field robots GNSS-Based Auto-Guidance Popular GPS Solutions Positioning Sensor DGPS (< in) RTK (< in) Terrain Compensation Gyroscope Multiple Units Vehicle Control Mechanical Hydroelectric Single Frequency Receivers WAAS, EGNOS, Beacon OmniSTAR VBS, John Deere SF Subscription/Free (sub-meter accuracy) Dual Frequency Receivers OmniSTAR HP/XP, John Deere SF Subscription (decimeter accuracy) RTK Receiver Base Station (centimeter accuracy)
Auto-Guidance Applicability What does ± actually mean? Sub-meter accuracy - ft year-to-year ft pass-to-pass Mechanical steering Decimeter accuracy in year-to-year in pass-to-pass Electro-hydraulic controls Centimeter accuracy in year-to-year in pass-to-pass Base station Tillage/Disking Spraying/Spreading Harvesting Seeding Mapping Planting Cultivating Bedding Strip Tilling Drip Tape Placement Land Leveling Topographic Mapping Nature of the test Cross-track error Static vs. dynamic Duration of the test Pass-to-pass vs. year-to-year Definition of the test Precision versus accuracy Statistic used %/σ vs. 9%/σ PI Guidance error versus GPS error Positioning vs. guidance error Auto-Guidance Error Auto-Guidance Field Day GNSS Positioning Error Vehicle Dynamics Guidance Error Implement Tracking Field Conditions August, ARDC, Mead, NE Field Demonstration Demonstration Course Pull-type cart J-type course Terrace crossing Coulter marker RTK-level GPS position logging Northing, m Contour pass Straight pass Starting point Easting, m
9...... Error Definition Error Distributions L A A A (X,Y) α LA L (X,Y) ε LA (XA,YA) L = L + L L L cosα cosα = sinα = cos α ε = L A sinα A ε = L + L L L L A A A L + L L A L AL A Cross-Track Error, in - - - - - Exact backtracking Product Demonstrated Contoured Straight - East Straight - West System System System System System Cross-track Error (cm) - - - - Error Distributions Signed error distribution Signed Error Unsigned Error Normal Model Rayleigh Model Zero Error Average Error Median Absolute Error Mean Absolute Error RMSE Unsigned error distribution Cummulutive Probability..9........ Cumulative Distribution Signed Error Unsigned Error Normal Model Rayleigh Model Zero Error 9% Threshold. - - - - Cross-Track Error, cm Field Day Results Producer-Viewed Differences Product RTK RTK RTK RTK RTK DGPS WAAS Product RTK RTK RTK RTK RTK DGPS WAAS Points Average Standard Deviation 9% PI p-value -.9... 9.9... -....99 -....99.... -........ Median Average RMSE Maximum Value 9% PI Value 9% PI Value 9% PI....... 9......9. 9.....9. 9....... 9.9..9...9.. 9.............. Error values are in cm Interface and ease of use Modes of operation Installation time and options Setup and calibration procedure Cost and possible upgrades Versatility and secondary use Technical support
NTTL Track Testing Linear Potentiometer System (LPS) Two straight parallel passes RTK Base Station Vertical support R Resistor array washers Common array washers V Reference GPS antennae Linear potentiometer Rw Rw Rw Rw Rw Rw Trigger Steel rod PVC tubing Nuts PVC spacer Test cart Trigger.9 cm Pilot Test System A Centimeter-level accuracy System B Decimeter-level accuracy LPS based analysis GPS based analysis Straight passes Three -min runs Two consecutive days Urban environment Concrete pavement Northing, m Test Sequence Test Run Test Run Test Run Test Run A-B line Easting, m North 9 triggers South triggers Spacing ft Swath ft
LPS Output Reference GPS Output Number of occurances Number of occurances -9. - 9. North North North South South South -. -. North North North South South South -. -. -. -. -. -. -9. -9. -. -. -. -. -. -. -.9..9.. Relative position, cm -.9..9.. Relative position, cm.. System A 9..... System B 9. 9..... 9. Northing (North pass), m.... R =.9..... North. South 9.. Linear (South) 9. Linear (North). R =.9.... Easting, m Northing (South pass), m System A centimeter accuracy System B decimeter accuracy System A - GPS reference (short-term error) System A - LPS reference (short-term error) System B - GPS reference (short-term error) System B - LPS reference (short-term error) - - - - - - - - - - - - - - - - System A - GPS reference (long-term error) System A - LPS reference (long-term error) System B - GPS reference (long-term error) System B - LPS reference (long-term error) - - - - - - - - - - - - - - - - Short-term term Error Long-term Error Cumulative short-term error distribution Cumulative long-term error distribution % 9% 9% probability % 9% 9% probability % % % % % % System A (LPS) System A (GPS) System B (LPS) System B (GPS) % % % % System A (LPS) System A (GPS) System B (LPS) System B (GPS) S A GPS (9%) % % % % % % % 9 Error, cm % 9 Error, cm
Test location Surface conditions Clarity of sky Test course segments Point of measurement Reference receiver Total station Mechanical (contact) sensor Optical (non-contact) sensor Discussion Items Test sequence PDOP requirements Pass-to-pass test Year-to-year test Error terms Dealing with bias Parametric and nonparametric estimates Machinery selection Tractors Sprayers http://bse.unl.edu/adamchuk E:mail: vadamchuk@unl.edu