Différences in Z for a same point

Hello,
I’m using Emlid Reach RS+ with real time corrections from ntrip.

For a same point, I have different Z (10-15 cm difference) although the solution is fixed for the 2 mesures. The two point were measured at one week intervals.

Point A 1.573 50.466 59.362 2019-05-09 12:42:16 UTC 2019-05-09 12:44:16 UTC FIX 0.0087 602 2.085
Point A 1.57329613277 50.4657222656 59.2101689655 2019-05-18 17:44:50 UTC 2019-05-18 17:45:36 UTC FIX 0.0186 232.0 2.085

How it is possible ? I precise that I’ve already checked the height of antenna and the ground can not moved.

Thank you !

At first glance it doesnt looks like those points are taken over the same area.
Whats the coordinates for each different point?

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THIS is the problem, it is the same point, same area, everything is the same except Z value :

longitude latitude height
Point A 1.57329613277 50.4657222656 59.2101689655
Point A 1.573 50.466 59.362

You see the different in Z ? And the solution were fixed for both of them. One week between those measures and no, the ground did not grow up :wink:

What is your baseline?
What are your RTK settings?
How many constellations enabled ?
How long are the measurements apart?

Seems like a bad fix in either of those two points, the position is different in all directions. The last point is lacking 4 decimals to be accurate.,

2 Likes

Ok, so I reloaded all the data. I measured the same point and there is one time where the Z is up to the error margin (2-3 cm) although the solution is fixed.

index name longitude latitude height collection start collection end solution status lateral rms sample count antenna height
12 Point A 1.57329665045 50.4657221188 59.3620598007 2019-05-09 12:42:16 UTC 2019-05-09 12:44:16 UTC FIX 0.0087 602.0 2.085
3 Point A 1.57329613277 50.4657222656 59.2101689655 2019-05-18 17:44:50 UTC 2019-05-18 17:45:36 UTC FIX 0.0186 232.0 2.085
4 Point A 1.5732958752 50.4657223673 59.209773913 2019-05-18 17:46:58 UTC 2019-05-18 17:47:12 UTC FIX 0.0234 69.0 2.085
5 Point A 1.57329597766 50.4657224531 59.2060380795 2019-05-18 17:47:14 UTC 2019-05-18 17:48:14 UTC FIX 0.0109 302.0 2.085
6 Point A 1.57329592064 50.4657224327 59.2473936364 2019-05-19 04:05:06 UTC 2019-05-19 04:05:51 UTC FIX 0.007 220.0 2.085
7 Point A 1.57329594746 50.4657223863 59.2370034247 2019-05-19 04:07:40 UTC 2019-05-19 04:08:39 UTC FIX 0.0098 292.0 2.085

why are you saying that the position is différent in all directions ? It is the same for XY up top 3-4 decimals ?

The base line is the french Orpheon Web
RTK Settings

RTK settings

How do you perform the measure?, static? are you pole fixed to a posisiton (hence not moving?
If the surface is flat and leveled, the XY should not matter for the Z value. Could you elaborate your workflow around this?
And data comming from ntrip, do you get enoug data? gps, glonass etc.

You need 7 decimals to achive cm accuracy. 6 decimals only gives you m accuracy

3 Likes

With a handled “stick” so it can move but very weakly, the surface is flat.

The data ntrip are coming from french orpheon web, maybe I’m wrong, but I was thinking that if the solution is fixed, so the measure is good isn’t it ?

Ok as I reply, i reload the data and there is 10 decimals

2 Likes

Usually it is, but if you`re in an area with obstruction, it could give you fals fix.
If you enable glonass AR and use continous this might improve this. Continuous is a more restrictive then fix&hold, it could be harder to obtain fix though

Vertical accuracy is also 2x times the accuracy of the horizontal.

Do you have log files you could share? rinex from base and rover

2 Likes

Not many obstructions here, it seems: https://www.google.com/maps/@50.4656776,1.5735418,3a,60y,298.11h,92.46t/data=!3m6!1e1!3m4!1sNCzIrBvx0gAz9o4EQjCaPQ!2e0!7i13312!8i6656

2 Likes

Do you have the raw data?
What was your baseline?

1 Like

Or a really poor VDOP

Indeed, coastal area so it is quite “free”

1 Like

I’m a beginner, VDOP ? Where did you read that ?

I can have the raw data for only the rover not the base (it is not in my subscription… :frowning: )

I’m downloading them.

The RTK settings were adviced from my dealer.

3 Likes

Here is some raw data for the fisrt line of the table.

Thank you guys for helping me !

https://drive.google.com/file/d/1XOI14Lb_MDMkdadgYP7bXlg7y1EgQxhY/view?usp=sharing

Did you also log the incoming correction-data ?