What does the "Station Details" information mean during stationing?

"Station Details" Reveals Positioning Confidence after Stationing

The "Station Details" screen will appear during stationing processes that require the total station to calculate a coordinate position in relation to the control points it measures, such as in control point stationing. In short, the station details reveal the potential errors, and level of confidence, in the coordinate positioning the total station calculated for itself.

It can be difficult (and intimidating) to try and interpret what the station details screen means. Therefore, while HCL will show the station positioning error details, it will also use other methods to provide visuals to help understand the implications of the errors seen in this details screen. Tools like tolerance settings and visuals like the green layout circle are very helpful to understand accuracy of stationing, for instance, and are very intuitive.

If you are struggling to understand the station details, therefore, try using tolerance settings and the visuals from the green layout circle to determine if your stationing accuracy is appropriate for your work. Below, however, the Station Details screen is explained in a bit more detail.

"Station Details" Explains Station Information from a "Best Fit" Scenario

If you remember the concept behind stationing with control points, the total station is simply measuring each control point, and determining how well the control point set up matches the way the control points are arranged in the digital design.

It is practical (and prudent) to assume that some errors will likely exist during stationing, as nobody is every perfect. Therefore, getting as much information about these errors is important in order to mitigate their effect during layout and measuring.

When the head unit measures each control point and attempts to match them to the design, it is performing a "best fit" analysis. In other words, it is determining which control points are likely more accurate than others based off the angles and measurements it is making between them, while also taking into account the distance measurements it is making from the head unit to the control points. There is a lot of triangulation occurring in the background.

With all of these different measurements - angular measurements and distance measurements - the total station then determines its coordinate location in relation to these control points. Again, this is after doing its "best fit" analysis with the control points provided.

Understanding "Station Details" - an Example

In the example below, you will see that I have measured 3 control points on my jobsite: CAT-4, FOIL-3, and CAT-1

You can tell that there are some errors amongst the measured points:

• FOIL-3 to CAT-4 has a distance that is 19mm shorter than the design
• CAT-4 to CAT-1 has a distance 4mm longer than the design
• CAT-1 to FOIL-3 has a distance 18mm shorter than the design

The total station observes this, and then finds a "best fit" for these control points to work together. It shows how it did this by showing the Station Information screen for your measured points:

For the "best fit" analysis, the total station recognized, most likely, that CAT-4 and CAT-1 were likely the better, or more accurate control points, and that FOIL-3 was likely leading to errors. Therefore, you can see how it "moved" the control points from their measured location to what would make them fit the best together.

For FOIL-3, for instance, it was moved 4mm to the south, and 19mm east of the plan's design.

After it does this best fit, it then reveals in the "Station Details" pane how confident it is that it is located at the coordinate it calculated for itself:

Notice that every value has a (+/-) icon. What this suggests is that at the coordinate location that the total station is determining for itself, it has a potential location error of 3mm north/south, 3mm east/west, a horizontal angle error of +/- 16 arc seconds of an angle. All of this leads, eventually to its "positioning" error of +/- 3mm.

What this means for your applications, therefore, will be best revealed by the green layout circle according to your tolerance settings. If you wonder if this is a "good" stationing, that is up to you to determine, as yes, errors exist, but the stationing process makes sure you have ample information to see what those errors might be and how they may affect your work.

Does errors in "Station Details" mean I will not be accurate?

It is important to unterstand that when you station a tool, it is simply calculating where the head unit's coordinate is located. After you station the tool, of course the total station will layout and measure points accurately by their design dimensions, taking into account the end user being careful to keep their prism pole level, set the correct weather conditions, etc. Many factors other than just positioning can affect accuracy.

When it comes to a "positioning" error, this means that if you were to come back another day and re-station on control points, there may be a small millimetric error in the location of the points between the different stationings day after day.

This is why a best practice is to establish very stable control points for your jobsite, and use them consistently throughout your project. It helps to keep your layout and measurements consistent and accurate day after day. See this article for more information on best practices for control points.