This guide explains how to apply the base shift in Emlid Flow to calibrate all further collected data in your survey project.
With the Base shift feature, Emlid Flow helps you calibrate your survey project data based on one point—it applies an XYZ shift to the base's ECEF coordinates in real time. The app calculates the difference between the known and measured points and applies a linear shift to all further collected points within one project.
Base shift can be applied independently of the used coordinate system—you can apply it to survey projects in local coordinate systems, for example, in UTM.
The Base shift feature helps you calibrate the survey data when there is a difference between the known and current base coordinates. You may need this in the following cases:
- When it is impractical to place your base over a permanent survey mark (PSM). For example, you cannot provide a clear sky view in this area, which may compromise the quality of the base logs.
- When you exceed the baseline and need to relocate your base.
The calculated shift is stored in the attributes of a particular survey project, applies to all further collected points, and cannot be auto-applied to another project.
Calibrate your base's position relative to a PSM
- Emlid Flow
This workflow describes the case when you want to survey the field using a permanent survey mark located in a hard-to-reach place. It is not convenient to install a tripod in this area or leave the base unattended. Or it is just simply a limited sky view that may compromise the quality of base logs. Here, the Base shift feature comes in handy—you can place your base in proper conditions nearby the permanent survey mark, collect the permanent survey mark with a rover and calibrate all further collected data in your survey project relative to it.
In this case, all you need is two points in the project:
- A known point, which is the PSM you want to calibrate with.
- A measured point, which is the same PSM collected with a rover in the field.
To calculate and apply base shift to your survey project data, follow the steps below:
Place your base and average its position in SINGLE.
Configure RTK communication between the base and the rover and wait for FIX.
Create a survey project in Emlid Flow.
Manually add a point with coordinates of your PSM and save it. This will be a known point.note
You can also do it later on the Base shift screen, tap Add a point and fill in the coordinates of your PSM.
Place the rover over the PSM and collect it. This will be a measured point.
Swipe up the project drawer and tap Base shift.
Tap Measured point.
Select the point that you collected. We called it 'Measured point'.
Tap Known point.
Select the point with the PSM coordinates. We called it 'Known point'. After that, the app will calculate the shift.
If you did not add a known point in advance, tap Add a point and fill in the coordinates of your PSM.
- Tap the Apply button to activate the shift.
When the shift is applied, you’ll see that it’s active in the project’s overview, and the rover icon on the map appears shifted.
Right from this moment, Emlid Flow starts applying base shift to all the points you collect further. In our case, it means that all points collected after base shift will be positioned exactly relative to the permanent survey mark.