GNSS Software and Trimble 4600's L1

> Well, I finally got up and running with GNSS software and my Trimble L-1 4600's. Instead of Post process kinematic I now use fast static. Instead of 40 sec observation and keeping satellite lock I now use 3 minute observations with no worry about satellite lock in between shots. But I do have to use a different file for every shot (an inconvenience but not too time consuming).

So, you're using rapid static solutions based upon three-minute occupations? What method are you using for examining the quality of those solutions? Aren't you a bit concerned that they are junk from such short sessions?

Times have changed since the field procedures were written for 4600LS ppkinematic and fast static. Today we have pdops in the 1.3 to 2.0 range and access 8-12 satellites (unheard of in the 1990's). I just worked on an existing subdivision, finding corners and checking against the record. Everything worked out within hundredths from the record with 3 minute observations in fast static mode, what follows is the Land Survey Report from Ashtech's GNSS:

Land Survey Overview

GNSS Solutions, Copyright (C) 2010 Ashtech. 10/12/2011 12:08:15 AM
www.ashtech.com

Project Name : WEDGE-B
Spatial Reference System : WEDGE-B
Time Zone : (GMT-06:00) Central Time (US & Canada)
Linear Units : US Feet

Coordinate System Summary
Coordinate system
Name : WEDGE-B
Type : Projected
Unit name : Meters
Meters per unit : 1
Vertical datum : Ellipsoid
Vertical unit : Meters
Meters per unit : 1
Datum
Name : WGS 84
Ellipsoid Name : WGS 84
Semi-major Axis : 6378137.000 m
Inverse Flattening : 298.257223563
DX to WGS84 : 0.0000 m
DY to WGS84 : 0.0000 m
DY to WGS84 : 0.0000 m
RX to WGS84 : 0.000000 "
RY to WGS84 : 0.000000 "
RZ to WGS84 : 0.000000 "
ppm to WGS84 : 0.000000000000
Projection
Projection Class : Ground_System_Azimuth
latitude_of_origin 47° 10' 17.65613"N
longitude_of_origin 100° 48' 09.02403"W
height_of_origin 624.074 m
azimuth_of_target 0° 00' 00.00000"
ground_easting 15238.642 m
ground_northing 15261.188 m

Control Points
95%
Name Components Error Status Control Error
1002 East 50460.808 0.000 FIXED
North 50007.488 0.000 FIXED
Ellips height 2054.532 0.000 FIXED

2002 East 47381.368 0.000 FIXED
North 49893.494 0.000 FIXED
Ellips height 2056.951 0.000 FIXED

Logged Points
95%
Name Components Error Status
2 East 47364.220 0.012 Adjusted
North 50061.151 0.017 Adjusted
Ellips height 2054.956 0.014 Adjusted

3025 East 47964.064 0.013 Adjusted
North 50002.891 0.018 Adjusted
Ellips height 2075.523 0.014 Adjusted

3026 East 48504.071 0.014 Adjusted
North 50004.506 0.019 Adjusted
Ellips height 2052.410 0.016 Adjusted

3027 East 49044.105 0.014 Adjusted
North 50006.191 0.020 Adjusted
Ellips height 2037.195 0.017 Adjusted

3028 East 49584.077 0.013 Adjusted
North 50007.743 0.018 Adjusted
Ellips height 2039.962 0.015 Adjusted

3029 East 50124.129 0.014 Adjusted
North 50009.420 0.020 Adjusted
Ellips height 2047.725 0.018 Adjusted

3030 East 50500.421 0.014 Adjusted
North 50010.630 0.018 Adjusted
Ellips height 2056.248 0.016 Adjusted

3336 East 49995.446 0.013 Adjusted
North 50069.413 0.019 Adjusted
Ellips height 2047.484 0.016 Adjusted

Files
Name Start Time Sampling Epochs Size (Kb) Type
71082830.11o 11/10/10 14:51 15 476 200 L1 GPS
70782830.11o 11/10/10 15:03 15 402 174 L1 GPS
77742837.11o 11/10/10 16:36 5 36 16 L1 GPS
77742830.11o 11/10/10 15:25 15 12 4 L1 GPS
77742831.11o 11/10/10 15:32 15 13 5 L1 GPS
77742832.11o 11/10/10 15:43 15 12 5 L1 GPS
77742833.11o 11/10/10 15:56 15 13 6 L1 GPS
77742834.11o 11/10/10 16:08 15 12 6 L1 GPS
77742835.11o 11/10/10 16:17 15 12 6 L1 GPS
77742836.11o 11/10/10 16:29 5 37 18 L1 GPS

Occupations
Site Start Time Time span Type File
1002 October 10 2011 14:51:00.00 01:58:45.00 Static 71082830.11o
2002 October 10 2011 15:03:00.00 01:40:15.00 Static 70782830.11o
2 October 10 2011 16:36:50.00 00:02:55.00 Static 77742837.11o
3030 October 10 2011 15:25:00.00 00:02:45.00 Static 77742830.11o
3336 October 10 2011 15:32:00.00 00:03:00.00 Static 77742831.11o
3029 October 10 2011 15:43:45.00 00:02:45.00 Static 77742832.11o
3028 October 10 2011 15:56:45.00 00:03:00.00 Static 77742833.11o
3027 October 10 2011 16:08:15.00 00:02:45.00 Static 77742834.11o
3026 October 10 2011 16:17:30.00 00:02:45.00 Static 77742835.11o
3025 October 10 2011 16:29:20.00 00:03:00.00 Static 77742836.11o

Processes
Reference Reference File Rover Rover File Mode Num
1002 71082830.11o 2002 70782830.11o Static 1
1002 71082830.11o 3030 77742830.11o Static 2
1002 71082830.11o 2002 77742837.11o Static 3
1002 71082830.11o 3336 77742831.11o Static 4
1002 71082830.11o 3029 77742832.11o Static 5
1002 71082830.11o 3028 77742833.11o Static 6
1002 71082830.11o 3027 77742834.11o Static 7
1002 71082830.11o 3025 77742836.11o Static 8
1002 71082830.11o 3026 77742835.11o Static 9
2002 70782830.11o 3025 77742836.11o Static 10
2002 70782830.11o 2002 77742837.11o Static 11
2002 70782830.11o 3028 77742833.11o Static 12
2002 70782830.11o 3026 77742835.11o Static 13
2002 70782830.11o 3030 77742830.11o Static 14
2002 70782830.11o 3336 77742831.11o Static 15
2002 70782830.11o 3027 77742834.11o Static 16
2002 70782830.11o 3029 77742832.11o Static 17

Processed and Adjusted Vectors

Kent, here are the processed and adjusted vectors:

Processed vectors
Vector 95% Vector 95%
Vector Identifier Length Error Components Error SV PDOP QA Solution
1002 - 3026 1956.625 0.049 X -1921.897 0.019 7 2.1 Fixed
11/10/10 16:17 Y 366.990 0.029
Z -3.641 0.004

1002 - 3030 39.770 0.039 X 39.118 0.014 7 2.0 Fixed
11/10/10 15:25 Y -6.324 0.023
Z 3.385 0.000

1002 - 2 3096.866 0.048 X -3033.874 0.018 8 2.2 Fixed
11/10/10 16:36 Y 620.355 0.028
Z 36.644 0.006

1002 - 3336 469.491 0.041 X -447.612 0.015 8 1.9 Fixed
11/10/10 15:32 Y 136.754 0.024
Z 36.922 0.001

1002 - 3029 336.735 0.045 X -329.528 0.016 8 1.9 Fixed
11/10/10 15:43 Y 69.198 0.028
Z -3.679 0.001

1002 - 3028 876.799 0.040 X -859.163 0.014 7 2.2 Fixed
11/10/10 15:56 Y 174.655 0.024
Z -10.512 0.002

1002 - 3027 1416.722 0.048 X -1389.339 0.018 8 1.7 Fixed
11/10/10 16:08 Y 276.863 0.028
Z -13.631 0.003

1002 - 2002 3081.365 0.017 X -3040.392 0.006 8 1.7 Fixed
11/10/10 15:03 Y 495.044 0.007
Z -75.869 0.007

1002 - 3025 2496.687 0.046 X -2455.420 0.018 8 2.0 Fixed
11/10/10 16:29 Y 451.898 0.027
Z 12.174 0.005

2002 - 3029 2745.062 0.055 X 2710.869 0.020 8 1.9 Fixed
11/10/10 15:43 Y -425.844 0.032
Z 72.188 0.005

2002 - 2 168.527 0.036 X 6.516 0.013 8 2.2 Fixed
11/10/10 16:36 Y 125.315 0.022
Z 112.494 0.000

2002 - 3028 2205.599 0.046 X 2181.228 0.017 7 2.2 Fixed
11/10/10 15:56 Y -320.382 0.027
Z 65.338 0.004

2002 - 3026 1128.120 0.045 X 1118.500 0.017 7 2.1 Fixed
11/10/10 16:17 Y -128.048 0.027
Z 72.226 0.002

2002 - 3030 3121.070 0.052 X 3079.516 0.020 7 2.0 Fixed
11/10/10 15:25 Y -501.373 0.030
Z 79.270 0.006

2002 - 3336 2619.853 0.050 X 2592.785 0.019 8 1.9 Fixed
11/10/10 15:32 Y -358.292 0.029
Z 112.792 0.005

2002 - 3027 1666.566 0.049 X 1651.050 0.018 8 1.7 Fixed
11/10/10 16:08 Y -218.175 0.029
Z 62.248 0.003

2002 - 3025 593.131 0.038 X 584.973 0.014 8 2.0 Fixed
11/10/10 16:29 Y -43.139 0.023
Z 88.036 0.001

Adjusted vectors
Vector Length Vector Tau
Vector Identifier Length Resid. Components Resid. Test QA
1002 - 3026 1956.624 0.003 X -1921.895 0.002
11/10/10 16:17 Y 366.992 0.003
Z -3.641 0.000

1002 - 3030 39.772 0.010 X 39.118 0.001
11/10/10 15:25 Y -6.326 -0.002
Z 3.394 0.009

1002 - 2 3096.868 0.009 X -3033.876 -0.001
11/10/10 16:36 Y 620.358 0.002
Z 36.636 -0.008

1002 - 3336 469.489 0.003 X -447.611 0.001
11/10/10 15:32 Y 136.752 -0.001
Z 36.924 0.002

1002 - 3029 336.734 0.001 X -329.526 0.001
11/10/10 15:43 Y 69.199 0.000
Z -3.679 0.000

1002 - 3028 876.800 0.009 X -859.164 -0.001
11/10/10 15:56 Y 174.657 0.002
Z -10.521 -0.008

1002 - 3027 1416.725 0.007 X -1389.341 -0.002
11/10/10 16:08 Y 276.865 0.002
Z -13.625 0.006

1002 - 2002 3081.366 0.003 X -3040.393 -0.001
11/10/10 15:03 Y 495.043 -0.002
Z -75.867 0.002

1002 - 3025 2496.688 0.004 X -2455.420 -0.000
11/10/10 16:29 Y 451.901 0.003
Z 12.172 -0.002

2002 - 3029 2745.060 0.002 X 2710.867 -0.002
11/10/10 15:43 Y -425.844 -0.000
Z 72.188 -0.000

2002 - 2 168.533 0.008 X 6.518 0.001
11/10/10 16:36 Y 125.315 0.000
Z 112.503 0.008

2002 - 3028 2205.602 0.009 X 2181.230 0.002
11/10/10 15:56 Y -320.385 -0.003
Z 65.346 0.008

2002 - 3026 1128.119 0.003 X 1118.499 -0.002
11/10/10 16:17 Y -128.050 -0.002
Z 72.225 -0.000

2002 - 3030 3121.065 0.011 X 3079.512 -0.004
11/10/10 15:25 Y -501.368 0.005
Z 79.261 -0.009

2002 - 3336 2619.850 0.004 X 2592.783 -0.003
11/10/10 15:32 Y -358.290 0.002
Z 112.791 -0.002

2002 - 3027 1666.568 0.007 X 1651.052 0.002
11/10/10 16:08 Y -218.177 -0.002
Z 62.242 -0.006

2002 - 3025 593.132 0.003 X 584.973 0.000
11/10/10 16:29 Y -43.142 -0.002
Z 88.038 0.002

Processed and Adjusted Vectors

> Kent, here are the processed and adjusted vectors:

What would give me pause about your survey is that you don't really have a network of independent vectors that you are using to demonstrate their reliability. Those are simply vector solutions to a roving receiver from two base receivers, aren't they?

The real test is to repeat the vectors at a time more than 20 minutes different. Otherwise both vector solutions based upon the same (short) rover occupation may have similar errors, don't you think?

I'm just mentioning this because the problem with the solutions from very short occupations is that those solutions can have statistics that make them appear to be reliable when they aren't.

What is the observation rate on the 3 minutes session? How many epochs are collected?

I hope 1 Hz.

> I hope 1 Hz.

Necessary for kinematic, detrimental for static, two reasons apparently:

• Statistics overly optimistic when processing using the higher data rate (time correlation not modeled)
• Floating solution converging too quickly, making it very sensitive to erroneous measurements at the start

Interesting, this post-processing stuff

> > I hope 1 Hz.
>
> Necessary for kinematic, detrimental for static, two reasons apparently:
>
>

• >
• Statistics overly optimistic when processing using the higher data rate (time correlation not modeled)
  >
• Floating solution converging too quickly, making it very sensitive to erroneous measurements at the start
  >

>
> Interesting, this post-processing stuff

So what you're saying Georges is that I probably would be better off with 30 sec. epochs running on my rover and base station? As it was I used 15 sec. epochs for both my rover and base station. I did do a couple of points with 5 sec. epochs on the rover but I didn't notice any difference in the results.

Kent, point well taken. But I was just locating existing pins in a subdivision so I had the record to check against but if I was doing "virgin" work a second independent observation would suffice.

True

You said...

"So what you're saying Georges is that I probably would be better off with 30 sec. epochs running on my rover and base station? As it was I used 15 sec. epochs for both my rover and base station. I did do a couple of points with 5 sec. epochs on the rover but I didn't notice any difference in the results."

Well in a nut shell, you SHOULDN'T see a difference! The processor can ONLY process those epochs that BOTH the Base & Rover have in common. If you base is collecting @ 30 seconds (or whatever), then your processor can only process 30 second data REGARDLESS of what is collected at the Rover (1s, 5s, 10s, 15s....).

IF you want to be able to process 5 second data (at the Rover), then your Base MUST also be collecting 5 second data. My base always collects 5 second data simply because the memory is there, and I never know what I might want to do at the Rover end (until I get there).

I always decimate the static data to 30 seconds for OPUS, and usually 15 seconds for my own post processing.

Loyal

True

For static processing, the suggested fastest observation rate is 10 seconds or less (15, 30, etc).

That's just what I understood from reading a user guide. Different processing engines may be built differently, I do not know.