Measuring Elevations with Laser Levels

How to Measure Elevation with a Laser Level

Laser levels are great bits of kit for providing accurate levels around a building or a construction site.

But only if you can use them right.

If you want to know how to measure elevation with a laser level, then you have come to the right place. I will share with you how to use laser levels for measuring elevations using over 20 years of experience at levelling with either auto (dumpy) levels or laser levels.

For the purpose of this article and to keep things simple I am going to ignore any affects due to the curvature of the earth. The current maximum range for rotating laser levels is about 800m (2600ft). And thus, the curvature of the earth is negligible.

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Let’s also understand what is meant when we say we want to measure an elevation with a laser level.

Defining Elevation

What is meant by the word elevation in this context? The definition of Elevation is height above a given level, especially sea level.

Understanding What a Laser Level Provides.

The laser level only provides a horizontal reference plane (sometimes referred to as a Datum) from which (perpendicular) measurements can be taken.

All laser levels provide a horizontal (and/or a vertical) reference plane. Nearly all laser levels are self-levelling as long as they are setup within 4 degrees of horizontal. Once the laser level has self-levelled, the laser beam from it will provide the horizontal reference plane from which all measurements can be taken.

The accuracy of laser levels can vary tremendously. It is important to select the right type of laser level for the type of work to be done. It is also important to check that your laser level is accurate. Because when a laser level is wrong it can have disastrous consequences.

How to Setup a Laser Level.

Select a suitable position for the laser level.

This can be one of the hardest parts in setting up a laser level. You want to place the laser level in a position where it will give the maximum coverage.

Minimise blind spots.

Choose a comfortable working height.

The laser level also needs to be set at a height that is convenient for taking measurements from. There is no point in struggling to reach the measurement points as this will induce more errors into your measurements.

Avoid measurement errors.

Setup the tripod and mount the laser level.

Set the tripod on firm ground and attach the laser level to the head of the tripod. The tripod head should be reasonably level. Adjust the level by adjusting the length of one of the tripod legs. Use the levelling bubble on the laser level if it has one.

Make sure that your tripod is in good condition.

Turn on the laser level.

Switch on the laser level and allow it to go through its self-levelling procedure. Once it has the laser beam will be working.

It is advisable not to look directly into the laser beam. If you are worried about damage to your eyesight, then I would recommend some laser safety glasses.

These are my recommended laser levels.

Work out the height of the laser level.

To work out the height of the laser level we need to measure vertically from a known level.

The height of the laser level is calculated by measuring from a TBM (Temporary BenchMark) to the height of the laser beam.

Inside a building (or home) this is most likely going to the floor level. This can have an arbitrary value in some corner. Measure from the floor and read the measurement from the centre of the laser line. Add this value to the floor level value. This will be your height of collimation or height of instrument.

But you should reference this should you have to move the laser level. Let’s refer to this arbitrary value as a TBM (Temporary BenchMark).

Outside, on construction sites we will have a TBM established before work commences. Measure from the TBM using an E-Grad staff and laser detector to find the height of the laser beam above the TBM. Add this measurement to the value of the TBM and this will be your height of collimation or height of instrument.

The TBM’s are often established during the initial survey of the site by a surveyor and determined using a GPS Network Rover.

Take the required measurements around the site.

Now that the height of the laser level beam is known we are now able to take measurements. These measurements are always taken perpendicular to the laser beam. Each measurement can be either subtracted from (for below the laser beam) or added to (for above the laser beam) the height of collimation giving a new elevation measurement.

How do Professionals shoot elevations with a laser level?

Professionals would shoot elevations with a laser level in a methodical way. They would have a procedure that they can rely on, check and other professionals could understand what they have been doing.

They would use an elevation levelling procedure.

When anyone needs to get the absolute level of points of interest, they need to ensure that it is done as accurately and precisely as possible. For this reason, not only should they use the best levelling equipment they can find, but they also need to use the best methods. It is very important to use the correct method to eliminate any errors that may affect our accuracy and precision when performing levelling operations or traversing. To achieve this, we need to follow a levelling procedure.

They would also need to record their observations in a certain way. The most commonly used method for booking elevation readings is the height of collimation method.

The topics for how to do an elevation levelling procedure and how to book a levelling procedure can be found in the articles below.

How to do an elevation levelling procedure.

How to book levels using the height of collimation method.

How to shoot elevations with a laser level easily.

Most professionals that use laser levels use them to make their working life easier. Often, they will have large areas that need to be the same level. Often the jobs take days or weeks to complete.

When they have large areas that are to be the same level, there will be Datum levels provided around the site. These datums will be set accurately by a site engineer or surveyor.

The laser level can be setup in the most convenient spot each day. Go to the relevant datum point. Set the laser detector at the correct level on the measuring staff and you are ready to go to work. That is the way to shoot elevations with a laser level easily.

How do you shoot elevation grades?

There are two different types of laser levels that can do sloping levels. These slope matching laser levels and grade (single and dual) laser levels. The main difference between the two (apart from the cost) is the amount to which they can be set from the horizontal or vertical plane.

The Slope Matching Laser Level.

A slope matching laser level is a horizontal laser level that the self-levelling feature can be manually altered to achieve a desired slope. These laser levels will always revert back to the horizontal plane when they are switched of and on again. Using the slope matching features of these laser levels is usually requires two people.

Slope matching laser levels currently available include:

Of the above slope matching laser levels, I prefer to use either the Leica Rugby 620 or the Topcon RL-H5A. I have used the GeoMax Zone 20H but I didn’t find it as accurate as either the Leica or Topcon.

There are reviews of these slope matching laser levels on this website.

Review of the GeoMax Zone 20H

Review of the Leica Rugby 620 Laser Level

Review of the Topcon RL-H5A Laser Level.

The Grade Laser Level.

Grade laser levels are available in two different formats. Either single grade or dual grade. Grade laser levels will self-level to horizontal. A specific grade for the works to be done can then be typed into the laser level, which will then adjust the laser beam to that grade.

A single grade laser level will only allow the desired grade to work along one axis of the grade laser. There will be a sighting line on the top of the laser level which will indicate the line of the axis that can be set. There will also be markings that indicate which way the slope will fall. A positive angle will indicate a rise from the laser level.

Dual grade laser levels allow for a grade to be set on either of the x or y axis of the level. Both axes can be set at the same time. Careful setup and alignment of the axes of the laser level is required when this is being used.

Grade Laser Levels currently available include:

  • Topcon RL-SV2S
  • Topcon RL-200
  • Leica Rugby 320SG
  • Leica Rugby 410DG
  • Spectra Precision GL412N
  • Spectra Precision GL422N

My choice from the above list would be either the Leica Rugby 410DG or the Topcon RL-SV2S. Both are very capable grade lasers.

I used a Leica Rugby 410 Laser Level and tested it for accuracy. This is because I have found that the Leica and Topcon Laser Levels to be the most accurate.

Why it is important to check a laser level.

I would recommend that site staff should check a rotating laser for accuracy every week. This site check should also be logged and stored with the Calibration Certificate for the rotating laser. Any deterioration in the accuracy of the rotating laser can then be easily identified and the rotating laser can be serviced and calibrated.

Using any piece of equipment that you haven’t checked could lead to disaster. Using a rotating laser that hasn’t been checked can lead to a costly mistake.

What happens when a laser level is wrong?

Take the case of steel erecting sub-contractor who started off putting up steel columns for a new steel frame garden centre building. He reported to the main contractor that some of the concrete bolt bases were high, so the contractor surveyed all the bases to find some of them to be no more than 5mm high and the contractor remedied the bases.

The steel erector sub-contractor continued erecting the steel frame building and after putting up more than 20 columns and the connecting beams he paid a visit to the contractor once more to notify them that next concrete base was so low that they couldn’t even fit it to the bolts.

The main contractor checked the base and found that it was at the correct level. Then main contractor’s site engineer then performed a simple two peg test on the Leica rotating laser to find that it was falling at a rate of over 1mm every metre.

When laser levels are wrong, costly mistakes are made.

The sub-contractor protested that he had a calibration certificate and that it should be right, but finally had to admit that his rotating laser was not fit for purpose.

After a full survey of the erected columns, the steel erector had to adjust at least 50% of the steel already erected, causing him lost time of 5 days that he couldn’t recover.

How to check a laser level.

Checking any Laser level for level accuracy uses the same principle as checking a dumpy or Automatic Level, which is we should have the same height difference of two points when measured from different positions and different lengths of sight.  However, there are more steps involved for the rotating laser check than a two peg test for checking an Automatic Level.

Remember that before setting up any rotating laser on a tripod, especially when checking for level accuracy, it is important to know that the tripod you are using is in good condition.  A test for the tripod can be found on the page test your tripod.

First, setup your tripod on a firm and sturdy surface, one that will support the weight of the tripod and rotating laser and an area not subject to vibrations from plant and machinery. Ensure the top of the tripod is level, use a spirit level if needed.

You should choose a position for the tripod that is close (1m to 2m from the rotating laser/tripod) to a suitable upright surface that can be marked on and another suitable upright surface ideally over 30m away.

Set the rotating laser on the tripod securely, square to the closest surface to be marked, and switch on and allow the laser to self-level and start up. You will be turning the rotating laser 90degrees three times during the test.

If you have a grade laser then ensure that the grades are set to 0% in all directions before attempting to carry out any checks.

With the rotating laser switched on you are ready to take some measurements. Turn on the receiver unit and select the fine tolerance setting for taking all the readings.

Place the receiver on the upright surface (wall) or using an E-Grad Staff in good condition and move up and down until the receiver is at the given level. Mark the wall with a suitable horizontal line or note down the reading take on the E-Grad Staff.

How to check a laser level

Now move to the other wall that is ideally over 30m away in either the opposite or perpendicular direction and place the receiver on the wall or staff and move up and down until the given level is achieved. Mark the wall with a suitable horizontal line or take a reading on the staff.

Return to the rotating laser and turn off the laser. Without moving the tripod, release the fixing screw enough to allow the laser to be rotated through 90 degrees.

Laser Level Checks

Switch the rotating laser back on and let it carry out its self-levelling procedure. Turn on the receiver unit and select the fine tolerance setting for taking all the readings.

Place the receiver on the upright surface (wall) or using an E-Grad Staff in good condition and move up and down until the receiver is at the given level. This should be the same level as before, but if there is a difference note this down.

Mark the wall with a suitable horizontal line or note down the reading take on the E-Grad Staff. Now move to the other wall and place the receiver on the wall or staff and move up and down until the given level is achieved.

Mark the wall with a suitable horizontal line or take a reading on the staff. At this point you should have the same level (or difference in level if noted) marked as the previous round. If there is a substantial difference in level (more than the specified manufacturer’s tolerance) then you should get the rotating laser serviced at your preferred survey equipment specialist.

how to check a laser level
laser level checks

If the levels taken are the same, then you should repeat the above process a further two times to check all planes that the rotating laser works in. If the rotating laser returns the same level each time, then all is good.