What is a Theodolite and how does it work?

A surveyor’s best friend, the theodolite is used for many purposes in their line of work. In this article we’re going to cover some common questions about them; what they’re used for, how to use one and how they work, along with the benefits of hiring one versus buying your own.

What is a theodolite used for?

To go right back to basics, a surveyor’s job is to make precise measurements of areas, usually for engineering, construction or mapmaking. The theodolite is essentially the most accurate instrument to measure the horizontal and vertical angles to work this out. But they can also be used for locating points on a line, prolonging survey lines and finding differences in elevation.

How do you use a theodolite?

1. Mark the point that the theodolite will be set up at, usually with a surveyor’s nail or a stake.

2. Place the tripod legs in the ground, making sure it’s at eye-level so measurements can still be taken, with the centre of the mounting plate directly above the nail or stake. Screw the theodolite on to the tripod.

3. Measure the height between the ground and the theodolite for reference to the later stations the theodolite will be set-up at.

4. Adjust the legs until you’re completely level horizontally, using the internal bull's-eye level and the fine-tuning knobs.

5. Now that it’s set-up horizontally, continue to make adjustments to the vertical plane using the vertical plummet on the bottom of the theodolite.

6. Aim the crosshair in the viewing scope at the point to be measured. Use the knobs on the theodolite to keep it aimed on the point.

7. The horizontal and vertical angles in the viewing scope are ready to be recorded.

How does a theodolite work?

Just about every theodolite in use these days is digital. Digital theodolites work by combining optical plummets, a spirit (much like a spirit level) and graduated circles to find vertical and horizontal angles. The plummet ensures placement exactly above the survey point. The spirit makes sure the device is level. The graduated circles, one vertical and one horizontal, allow the user to actually survey the angles.

Hiring vs. buying

This question all comes down to your individual needs, if you will be using it frequently and over a long period of time, buying a theodolite outright can be the right choice. However, even with regular use there are still drawbacks to buying outright, such as not having the latest technology, being responsible for servicing and maintenance and having a depreciating asset.

Another great benefit to hiring is being able to use the support and expertise of our team, if you want to hire a theodolite, send us a message or call the team 13 15 52.