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Benchmarking for MEP

Products Covered: Trimble Field Link for MEP

Benchmarking with Trimble Field Link and the Robotic Total Station

Your Robotic total station helps you to lay out points that the CAD/Coordination Department has assigned to 3D coordinated objects you are responsible for laying out on the project.  Some points may have different elevation relationships to each other and also the level you are trying to lay them out on.

Benchmarking is a way that you can control how you lay out your work.  You can also use it to your advantage to manipulate your point data for faster layout.

What is a benchmark?

A benchmark is a precisely measured elevation or height assigned to an object on the job site. A couple examples of this could be a property pin that is 5,280’ above sea level, or an architect assigning an elevation of 100’ to Level One of a building.

Once a benchmark has been established in the Robotic Total Station, the elevation of all other points measured there-after are relative to the benchmark elevation. For example, if a finished floor has a benchmark of 0’-0”, and the elevation value of a layout point is 9’-6”, then the point would be laid out at 9’-6” above the floor (example 1).  Likewise, if that same floor has a benchmark of 100’-0”, and the elevation value of a layout point is 109’-6” then the point would still be laid out at 9’-6” above the floor.  Even though the values have changed the relationship between is still 9’-6” (example 2).

Example: 1
Example 1

Example: 2
Example 2

In the above examples weather you benchmark at 0’ or 100’ the point is always 9’-6” above the floor.  The problem arises if you benchmark the floor( in example 2) at 0’ then the robot thinks the point you want to layout is actually 100’ higher than it really is because it’s value is 109’-6” above 0’.

This can get a bit confusing if you have many points at many different elevations.  I’ve come up with some steps to help you take some of the guess work, and hopefully frustration, out of your benchmarking challenges.

Benchmarking in Four Easy Steps (EMSM)

  • What is the ELEVATION of the point I want to lay out?
  • What METHOD do I want to use to lay the point out with?
    • Prism (Make sure you enter your rod height)
    • Laser
  • What SURFACE do I want to lay the point out on? 
    • Floor
    • Ceiling
  • Assign your elevation value and MEASURE your mark.

The following (example 3) represents this work flow.

Example: 3
Example 1

In this example my original point elevation is 9’-6”.  I want to use the laser as my layout method.  The surface I want to lay out on is the ceiling.  Finally, I specify my measurement value of 9’-6”; point my laser at the ceiling, and measure.

Now when I tell my robot to aim at each point it will always look up at the ceiling provided all the points I’m laying out have a similar value.  Even though the ceiling may not be 9’-6” when I use benchmarking I’ve tricked the robot into looking where I want it to and am able to lay my work out in a manner that is more efficient for me(example 4).

Example: 4
Example 4

If I want to lay points out on the floor the process is similar except I will point the laser at the floor and measure it at the 9’-6”.

Tip:

Concrete floors and ceilings can be inconsistent at best.  If the Surveyor has marked a horizontal line on a vertical surface and given it a value, that’s a great reference line immune to job site inconsistencies.