How do I Troubleshoot Inaccuracies in Stationing, Control, or Layout?

Anytime you struggle to maintain accuracy on a jobsite, please first ensure that you are working with the correct and most current digital files by consulting your drafter, surveyor, or general contractor. In addition, verify that the in-field conditions for control (whether points or line work) matches the digital file you have been given. Once that has been confirmed, Hilti Construction Layout software can help you stay accurate during your layout and measuring applicaitons.

Firstly: How does HCL help check accuracy as I work?

The Hilti Construction Layout software ensures that you have full visibility and understanding regarding the accuracy of your data and layout - from start to finish. Ensure that you are checking for accuracy at each crucial stage of the layout process.

1. During data import: perform basic checks on the data to ensure it is imported correctly.
   • Use COGO applications to verify all lines and points are imported with distances and locations as expected
   • Use layers and CAD view to ensure everything needed is visible
2. During stationing: observe the errors of your control points or stationing process as you station; see the specific articles below to see how this is possible with each stationing method.
   • Control Point Stationing (most common)
   • Control Line Stationing
   • Reference Line Stationing
   • Free Stationing
   • Over Control Point
   • Line Over Point
3. During Layout/Measuring Applications: observe the deviations or measured location of points to verify they are accurate to the design; see articles below depending on your workflow.
   • Backsight Check - link back to a pre-saved control point to see if your station has moved
   • Point layout - stake points and observe deviations as you layout
   • Line layout - easily observe deviations from lines and visualize your location on your plan
   • Measure and record - record points in your plan and observe their location in relation to your design
   • Field Calibration - perform field calibrations at anytime to ensure accuracy
4. After Work is Complete: export reports to clearly understand how work was done and where/why inaccuracies may have occurred:
   • Stationing Reports - observe each stationing performed: the control points used, PPM settings, time and date settings, and the calculated stationing accuracy.
   • Deviation Reports - observe the points that were staked and laid out and the deviations relative to their designed location
   • Point Exports (see bottom of linked article) - see detailed data for each point within your project: staked point location, station and prism used during staking, PPM at time of staking, etc. 

Now, to go into more detail, please see the remainder of the article.

1. Hardware: Check that the tool is calibrated properly

If you are doing any measurements with a total station, it is important to first make sure that the total station is properly set up to read measurements accurately.

Please perform the following checks to make sure your total station is prepared to read measurements accurately:

1. Set the correct PPM and acclimate to the weather (see this article)
2. Verify your prism pole (if being used) is truly plumb and level (see this article)
3. Ensure the total station is stable and secure (see this article)

4. Run a field calibration of the tool (see this article)

   

If you have verified that all these things are complete, your tool is in good condition to read measurements accurately.

2. Imported Files: Check your digital file measurement data is accurate via COGO applications

Most often, stationing and layout inaccuracies have to do with the data that is imported into the tablet rather than the control points in the field themselves. So, it is always good practice to check your digital data set up before moving on to other troubleshooting methods.

Any of the following functions on the tablet can help clarify the control point dimensions your data, as imported, is asking for:

1. Distance between points
2. Line and offset
3. Length of line, arc or circle
4. Distance between parallel lines
5. Angle 3 pts

Feel free to use any of these data measurement features to check the data within your file on the tablet. If the measurements seem off digitally, they will certainly be off in the field.

If you notice that this is where your errors are likely coming from, try to re-import your data (as it may have been imported with the incorrect units), or, discuss with a surveyor, general contractor, designer, or someone in charge of your control to discuss why the digital file is not reading properly.

3. Real-World Conditions: Check the in-field measurements with basic HCL applications

If the digital file seems to be reading correctly on the tablet, but you are still not able to station with the control points that have been given you, it is likely that the control points in the field are either the wrong ones, or are not placed correctly to what the digital file is expecting.

HCL allows you to use the total station to quickly verify in-field measurements by using applications that do not require formal control points. You can just turn the tool on and start verifying various measurements.

Basic Method 1: Missing Line application

The "missing line" application is a glorified tape measure that can read not only horizontal distances, but also slope, height, and angles between two points.

After you have verified the distance (and/or angles) that are supposed to exist between your control points, simply open up "missing line" and start measuring between the points. As you measure, verify that the data "missing line" is giving you matches what your digital file says should be there. If it does not match, discuss your findings with the surveyor, GC, or perhaps the designer.

Basic Method 2: Use Free Stationing to see an "As Built" of your in-field control

It can be very helpful to create a new project and use the "free stationing" application to start measuring and recording points in an open space. It lets you visualize the existing in-field control points you have been given to work with and lets you develop a report, of sorts, that you can show stake holders. This process will help to identify any issues with control points between the digital design and what is provided in the field.

Create a new project on the tablet and go to "free stationing" to arbitrarily station the tool in your area.

Then, open the measure and record application to start measuring in the various control points (or anything of pertinence) in your jobsite area. You can then use the on-tablet data measuring functions mentioned above to check the measurements and angles between your points, and then compare that to what you have on the digital file.

4. Perform a Basic Stationing

This step is for customers who want or need to utilize multiple control points, but only have verified the accuracy of 2 or 3. It is still possible to station on as little as 2 control points, which you can then use to troubleshoot the possible inaccuracies of the control points you do not yet trust.

For this troubleshooting step, begin by stationing the tool only with your accurate control points, or, the ones you are confident in. Then, use the measure and record application to plot the other control points on your jobsite. It should be clear how far they deviate from the way the control points were designed on the plan. Just compare the measured point to the designed point you see on your screen and share the info with your team.

Hopefully, this data can help determine if and how your team will re-establish control points for long-term accuracy on the jobsite.

5. Additional Backsight Checks

This section is critical once you have established an accurate stationing on your jobsite.

In addition to the backsight function already mentioned, you can add one more layer of accuracy security by adding a manual backsight location (or multiple locations). These backsight points can be used as temporary accuracy checks throughout your work day.

Once you have completed an accurate stationing, go into measure and record to measure in a new measured point at a location of your choosing. This point will be your backsight point, or reference point, throughout the work day. After you perform layout for a certain period of time (perhaps 1 hour), simply turn your tool back to this backsight point and observe if you are experiencing any significant deviations.

When you station the next day, turn back to the backsight point again to see if there are significant deviations from the previous stationing.

By having this best practice, you can always check if you are maintaining accuracy in your layout day after day, and can remedy the situation in a timely manner by noticing problems sooner rather than later.