# What is the difference between the Base shift and Localization features in Emlid Flow?

In our previous post, we told you about the Localization feature in the Emlid Flow app, and some of you asked how Base shift differs from it. Let’s take a look:

Apply localization when you don’t have the coordinate system parameters, or they are not accurate enough.

Localization is the process of comparing sets of known and measured point coordinates to calculate or adjust the parameters of the local coordinate system. To do this, the app applies a series of transformations and adjusts all the points within the project. The process requires a set of data—starting with the control points and ending with the available coordinate system parameters. To learn more about the workflow, see our guide about performing localization in Emlid Flow.

Apply base shift when you cannot place your base over a known point because it’s located in a hard-to-reach or obstructed area or when, for some reason, you cannot use it anymore.

Base shift is the process of comparing the known and measured coordinates of one and the same point to shift the rover’s position. To do this, the app applies a basic linear shift to the coordinates of the base in real time, and all points collected after base shift are positioned exactly relative to the adjusted base’s position. All you need are the coordinates of the known point or a permanent survey mark, no additional data is required. See our guide about applying base shift in the Emlid Flow app for the steps.

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I think I am little confused about the Base Shift feature… I am probably overanalyzing something simple here ; )

In a BASE / ROVER setup, typically set up BASE over a KNOWN POINT using coordinates and elevation from a public record for that KNOWN POINT.

But say I cannot set up the BASE over that point because a HUGE DUMP TRUCK is on top of it? ; )

So I set the BASE up maybe 50’ arbitrarily away.

So how does BASE SHIFT know where to shift my observed points if I cannot set up on top of the KNOWN POINT?

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Being able to apply a base shift requires that you are able to use a rover on the Known Point in order to calculate the shift.

Take this example. You have a Known point on the sidewalk at a busy intersection near where you plan to survey. Instead of setting up your base on that Known Point next to traffic, you want to set up your base in a parking lot nearby instead, but you want all the points that you collect to reference that Known Point, not where you are setting up your base in the parking lot. You could use the base shift workflow for that.

Read through the guide and it should make sense.

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thank you @dpitman

That was a very easy good explanation! Basically instead of leaving the BASE sit in the intersection, can just grab the point quickly dodging cars with the ROVER! ; )

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Exactly! You got it!

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Nice and clear comment, Dave! Thank you. Fully agree.

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Question:
base shift only applies to the rover, it corrects the data there?
Using the example above with the dump truck
I use my base as an RTK NTRIP output after measuring a few GCPs.
When I measure a few benchmarks, they are all off by 35mm North, I need to adjust my base position by 35mm South to get them all spot on. Using base shift would do this easily if I was only measuring and recording GCPs, but I’m also flying RTK.
My base needs to be accurately setup relative to the last time it was used on this site to get accurate cut fill measurement with my RTK drone. Applying base shift in this case would do nothing for that accuracy.
Is there an easy way for me to get the data on how many degrees lat/long I have to add/remove from my base position?
Am I wrong in my assumption that the base coordinates are unaffected by base shift?
Joe

Hi Joe,