How to correct collected points with a new base position?

In this post, we’ll explain how to collect points in RTK with relative accuracy and correct them with a new base position afterward.

When you may need that? Remember we discussed how you can obtain precise coordinates in a remote area with no cellular network available? We told about PPP technique there, which can be used to find a known point for your base to collect points with absolute accuracy. Also, for this purpose, you can use AUSPOS or OPUS services.

But this workflow may take time: you need to go to a site, record raw data logs, process them to get base position, and then return to collect points in RTK with absolute accuracy. Sometimes, you don’t have enough time or just can’t attend a survey site twice.

Here is an alternative workflow:

In the field

  1. Average the base position in SINGLE.
  2. Write down the averaged coordinates.
  3. Go to the Logging tab and choose one of the presets we have in Emlid Flow (formerly known as ReachView 3). They were made to match the requirements of different PPP, AUSPOS, or OPUS services.
  4. Start raw data log recording on the base.
  5. Collect points with the rover in RTK.

In the office

  1. After the survey, download the raw data log from the base and submit it to the chosen PPP service, AUSPOS, or OPUS.

  2. To calculate the shift between the new position and the base coordinates averaged in the field, subtract one coordinate from another. For example, in Excel.

    But there is a pitfall: they should be in the same coordinate system. I’d suggest converting both of them to the coordinate system of your Emlid Flow project. Base coordinates averaged in SINGLE are always in WGS84.

  3. Once you’ve calculated the difference, add it to the coordinates of the collected points. It can also be done in Excel, for instance.

A similar workflow can be used if you got a new base position by processing its logs with logs from the NTRIP service. If this case requires clarification, don’t hesitate to ask!

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Regarding this matter, I have a suggestion. Once we define an averaged point for our base, The app could save it as a surveyed point. It would make everything easier. Currently, I export as a .csv and create a point for the Base, by copying and pasting the coordinates from “Base Easting”, “Base Northing”, and “Base Elevation”. For “Base Elevation” I subtract the distance from the ground to the bottom of the receiver, as well as the antenna offset.

Hi Rafael,

I have good news! In another Support tip post, we wrote that it’s possible to do starting from 30 Beta 1:

Starting from the 30 Beta 1 Reach firmware, if you go to Manual entry after averaging and specifying the antenna height, Emlid Flow will calculate the point on the ground. You can save this position and use it for future surveys.

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Hi Svetlanna. That sounds excellent.
Thanks for the heads up!

Rafael

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