What does the Green Layout Circle Represent when Stationing?

The Green Layout Circle is a Tolerance Guide

When using control points during the stationing process, the total station will first verify how accurate the measured control points are to the digital design. If there are any measurement errors, regardless how small, the tool will calculate what level of accuracy it can perform applications when using your control point measurements.

The green circle that appears after you station with control points represents the work area that will be consistent with the tolerance you have set. If you have 4mm set in your 2D layout settings (meaning you do not want to be more than 4mm off amongst your measurements), the software will only turn green over the area that it can confidently guide you to that level of accuracy.

This means that outside this range, it is unlikely that the desired accuracy will be achieved. Conversely, if you are within the area outlined by the green circle, you can reasonably expect to achieve this accuracy.

Please note: this accuracy estimate does not take into account other factors that may affect accuracy, such as prism rod leveling, ground marking mistakes, or any other step in your procedure that may introduce errors.

Examples of how the Layout Circle Helps:

Easily See Bad Stationing Set Ups:

Take the below example. The software is helping me understand that my stationing set up is likely not optimal:

I have measured in 2 control points. You can see in the bottom right hand corner of the screen that my "layout tolerance" is 10mm. Using only two control points, and based on how accurate my measurements were, the software is warning me that the total station will only be able to guide me to a 10mm accuracy in the small area indicated by the circle. Anything else outside of that, and it is likely to be inaccurate.

Should I use this stationing? Likely not. I should find a better control point set up.

Now notice what happens when I increase my tolerance to be 4mm in accuracy:

The software will not be able to show me a layout circle - suggesting that the control point set up I have is too poor to layout to 4mm accuracy.

Easily See how Your Control Points Influence your Accuracy Potential:

Now, with keeping the example above, let's see what happens to the layout circle as we add more control points. I will keep my tolerance settings at 4mm for 2D layout:

Below you see that I have now measured in 8 different control points around my jobsite, and finally, I was given a layout circle that suggests what where my 4mm accuracy requirements can be maintained.

Here is what that layout circle looks like if I want to maintain a 6mm accuracy:

How can you optimize the layout circle?

Outside of simply ensuring you have accurate control points to work with, the software offers some helpful tools to optimize the layout circle as best as possible.

Once you measure in your control points, navigate to the "Measurements" tab in the top right corner. It will show you each control point you measured, as well as the deviation values among them. For a quick definition, those deviation values reflect how much the tool had to adjust that control point's measured location to get it to "fit" with the digital design.

By default, the software uses all the control points you measure in to calculate the layout circle you intend to work with. However, you have the ability to manually remove, or have the software automatically deduce, the control points that are likely inaccurate and hurting your potential accuracy for measuring and layout.

For example, let's click "Suggest best selection" from the above list to see if the software can remove some poorly measured control points in the stationing calculation:

What you see is that the software was able to find control points that would allow you to layout with the highest accuracy possible, given the control points you provided. At 4mm layout accuracy, I can confidently layout my entire jobsite area.

How does my Layout Tolerance Setting affect how Accurate I am when I Layout?

The total station will always guide you to be as accurate as possible, regardless of the tolerance setting you have in the tool. The tolerance setting has two basic functions:

1. Have applications turn green or red during your work to give you a visual of measurements that are within or outside of your set tolerance.

   • For example, at 6mm tolerance during layout, the crosshairs of your location will only turn green once you get within 6mm of your point like the screenshot below.

2. Show realistic working areas that will keep you to your tolerance during the stationing process (as discussed in this article)

Regardless of your tolerance, the tool will always guide you to what is calculated as a "0" location for your points, relative to the stationing you have performed with the tool. If the calculated position of these points is off, however, simply depends on the care the end user takes to station the tool accurately and keep it accurate during the working day.

For further help on accuracy topics please see this article.