Surveyed points and logged track disagree by similar distance each time

[Fenrir (Luke)]

In brief, here’s the google earth overlay. Ignore the image’s marked field lines, which are obviously wonky (and 3 years ago), and that google imagery isn’t always located very well (although the permanent 0m and 100m lines, and shotput waypoints seem perfect…). The important point is that I marked the points at the intersections of the field lines, which are where I turned and walked across the field, yet it appears all my waypoints are about 1.5m south of these intersections. It also appears the waypoints don’t line up with where I stood for a minute collecting the points.

In detail:
I walked an RTK survey today of a local sports field. I created a survey and marked points along the boundary lines, at their intersecting meter lines. I had fix the entire time, using all satellites other than Glonass (30 satellites! ), and a local reach radio base station in the centre of the field that I located using 10 minutes of fix from a NTRIP station 65km south. The survey points were taken during the same time period as I walked the perimeter of the field, then I walked the horizontal tracks of the lines (in the same log file)

At first I assumed the icons weren’t indicating the actual position, however the waypoint latitude and longitude don’t line up with the mouse-over lat,lon of the intersections either. I then assumed maybe it was a projection error, but everything is set to WGS84/EPSG:4326. I don’t think I’ve done anything silly like including an offset during kml generation, etc.

Reach 2.8, RTK tools b27, reach (non-rs) rtk kit.
Here are my logfiles if needed:Oval-GeoJSON.zip (2.5 KB)
base_201709070705_RTCM3.zip (2.7 MB)
raw_201709070705_UBX.zip (9.4 MB)

I cut the first few minutes of the rover log in my kml to remove walking to the start position and setting up.

Also, I noticed the single solution plot is pretty good, just thought I’d show it off. I postprocessed the same log without base corrections: Blue is dgps, red is single.

So TL:DR is, does anyone know why survey points don’t line up with logged tracks? Should I trust the survey points, or the track? Can I better process the logs to fit the surveyed points better in the future?

Thanks for your time.

[TB_RTK]

Just a quick question. Did you use fix&hold?

[dmitriy.ershov]

The best guess is that you didn’t set the base coordinate for post processing for the same value as during RTK work.

[Fenrir (Luke)]

Ah, you’re correct. Well spotted! I grabbed the co-ordinates I used on my base reach during surveying and re-processed the rover log with those co-ordinates and it’s perfect.

My mistake was post-processing my base position and using the average co-ordinates from the hour or so of log for the rover post-processing, but only using the first 10 minutes of fix averaging to set the base co-ordinates used in the survey.

Thanks to you both for your help.

[Simon_Allen]

I have a similar but slightly different problem.
I used a 5 minute FIX average to set up my base This gave:
-42.8936957001N 147.494136.065E and Ht 0.663m (the reference was Hobart AusPOS site)

When I look in my Rinex Header (if I process my rover using rinex header base position) I see the rinex header reads:
ref pos :-42.893683421 147.494123077 16.9164

Why are these numbers different?

[dilipatil24]

hello dude, how much time takes to come in fix mode? can u say me

[Fenrir (Luke)]

It really depends on your conditions. I had pretty perfect satellites with all constellations other than glonass enabled, for a total of 30 satellites in view. My reach base station was on static mode with a ntrip correction 65km away, and after a hot start I would say within several minutes on average. Some times it takes 10 minutes, other times it takes 1. I think most recently my base station didn’t get fix for 10 minutes, but once I started my rover it got and held fix within 2 minutes. There should be plenty of discussion around these forums on other users typical experience getting fix, how they set up their equipment, and their personal anecdotes.