Thinking of Buying a Total Station? This article should help you decide which total station is for you.
What is a Total Station?
A Total Station is an instrument that measures both horizontal and vertical angles and distances. It used by Engineers and Surveyors for setting out 3-dimensional points and for recording 3-dimensional points. Total Stations were invented when an EDM (Electro-Magnetic Distance Measurement) device was added to a theodolite. Originally these were mounted on top of the telescope of the theodolite, but during the 1990’s the EDM was incorporated into the telescope and the Total Station as we know it today was born.
Do I need a Total Station?
If you need to measure accurately within a radius of 500m then a Total Station would be an ideal instrument for you. A Total Station can be capable of measuring a point to within a few millimetres anywhere within ½ km from the instrument. That is not to say that a Total Station can’t measure further than this, but when using a Total Station, it would be advisable to keep within this working range for a single setup.
What types of Total Station are available?
There are many different types of Total Station available to buy and the one that is right for you will depend on the work that you undertake. When talking about the types of Total Station we are referring to what tasks and operations can be performed with them. We generally class them into types as Non-Reflectorless and Reflectorless, and either as two-man or one-man Total Stations.
The Basic two-man Non-Reflectorless Total Station.
This Total Station can only measure distances to a prism and requires two people to work as a team. The Basic Total Station as its name suggests is the least sophisticated of the Total Station range. It requires the user to be at the Total Station and a chainman or rod man to hold the prism at points around the site. These Total Stations should be easy to setup and easy to use with basic functions and displays that would show only angles and distances or co-ordinates. With this type of Total Station, it would be advisable not to rely on the elevation data given and that subsequent levelling of all points be undertaken with a suitable Automatic (Dumpy) Level. This Total Station would be best suited to small sites with minimal points to set out.
The two-man Reflectorless Total Station.
This Total Station is just like the Basic Total Station above but has the enhanced capability of being able to measure without the need of a prism to reflect the signal back to the Total Station. At this point the capability (and the price) can be huge from the most basic to a Total Station that can have some advanced features and functions. This Total Station still requires a two-man team to operate and to fully utilise for either setting out or surveying, although it would be possible to operate without a chainman or rod-man if only reflectorless measurements were to be done. A reflectorless Total Station is necessary where measurements to an inaccessible vertical face are required, an example of this would be in a quarry when needing to calculate an excavation volume.
The one-man or Robotic Total Station.
This is the most advanced Total Station usually found on construction sites and is used by experienced engineers and surveyors. As its name suggests, it can be used and operated by a single person. These Total Stations have the ability to track a prism and with a remote control (referred to as a Data Logger) handset can be operated by just one person. Depending on the manufacturer, these prisms have either an active tracking system or a passive tracking system. One major advantage of these Robotic Total Stations is that the potential accuracy is greater as the engineer or surveyor is holding the detail pole and when measurement are taken they can be sure that the detail pole is being held plumb, thus reducing erroneous errors. These Robotic Total Stations can also be used for machine control applications. This is where information on position can be supplied to an excavator or dozer so that it can follow, or work to, a pre-defined DTM (Digital Terrain Map) model.
What is the accuracy of a Total Station?
The accuracy of a Total Station is always quoted in seconds, which is an angular measurement. The lower the number the greater the accuracy of the Total Station. There is also an accuracy that can be achieved with the distance measurement, however this is rarely quoted. The most common quoted accuracies for Total Stations are 10 Seconds, 5 Seconds, 3 Seconds and 1 Second. To put these accuracies into figures that we can all readily understand we need to express these as dimensions at set distances from the Total Station. The below table illustrates the accuracy of angular measurements.
Table of Total Station Potential Errors at Specific Distances as measured from the Total Station.
It should be remembered that the potential errors given in the above table should be primarily considered in plan only for the very basic Total Stations. For the more advanced Total Stations, like the Robotic Total Stations, the potential errors should be considered as a diameter around the point being measured.
The above table does not take into account any errors associated with the distance measurement that is done by the Total Station. The accuracy of the distance measurements varies from instrument to instrument and are also affected by atmospheric conditions. Most Total Stations will measure to an accuracy better than 5mm. This is however affected by the mode of the measurement being taken, for example when tracking a prism, the accuracy would be less than fixed prism being measured in precise mode. There is also an atmospheric constant to be considered and the amount is expressed in PPM (Parts Per Million). This only has an affect when taking very long distances and would only practically used with the most accurate of Total Stations.
Which Brand of Total Station should I buy?
If you are considering the basic non-reflectorless Total Station, then choosing any brand of Total Station would be fine. A more important consideration for the basic Total Station is the support available once you have bought the Total Station. As you start using the Total Station you may well have lots of questions about how to use it or how to do things better and the support and knowledge of your local dealer or supplier will be very valuable.
If you are looking at buying a Total Station that is at the higher end of the market, like a Robotic Total Station, then it would be best to go for one of the leading manufacturers like Leica, Topcon or Trimble. But when considering choosing which manufacturer to choose consideration should be given to which desktop software you prefer. This is because the type and amount of data that you will be using will be significant and choosing the right software and manufacturer will greatly improve your efficiency. Leica don’t seem to have their own software like Trimble and Topcon, so you are left with third party solutions like LSS or N4CE. Trimble have either their Business Centre Software or TerraModel. Topcon have their Magnet Office software which has been developed over the years from CivilCad to SurveyMaster and now to Magnet Office. You should try out the numerous software that is available, most companies will offer a free trial of their software, and find one that suits your work flow.
Over the years I have tried all of the software and have found one I like and that I can use proficiently now, but I have also found ones that I hated and couldn’t get on with. It is all down to personal preference, but it will make a huge difference to your performance and ability to work the more advanced Total Stations. It is an important part on choosing a brand of Total Station as the benefits of having the right CAD software and Total Station for you are huge.
What are the important factors when buying a Total Station?
Accuracy is the most important consideration for purchasing a Total Station. Your decision will be based on the type of work you will be using it for and the distances over which you will be measuring. Look at the table above, Total Station Potential Errors at Specific Distances, and use it to check that you are going to be able to use it get the accuracy you need. Think of it this way, if the point I need to mark out or record needs to be within 5mm of the required position and I am 500m away then a Total Station of either 10- or 5-seconds accuracy would not be accurate enough for this task.
Non Reflectorless or Reflectorless.
This has to be one of the best features of the modern Total Station. Being able to measure to most surfaces is major bonus to Total Stations, and to the engineers and surveyors using them. It is possible the best time saving function on a Total Station when it comes to surveying and setting out. Imagine the amount of time saved by surveying walls, trees, columns and fences by not waiting for your chainman or rod-man to walk between all these features. Reflectorless Total Stations provide a massive leap in the productivity of engineers and surveyors. I would only consider buying a total station that had reflectorless capabilities.
Programmes or Functions.
The additional programmes and functions that are available on Total Stations have a big impact on the usability and productivity that can be achieved.
Being able to set the Total Station anywhere on the site and to be able to know accurately its position thanks to the free-station programme. This means that you are no longer restricted to setting up a Total Station above known points.
Leica Total Stations have a very good traverse programme for an additional cost. Using this programme and their prism stations makes completing traverse networks easy and straightforward.
The more powerful Total Stations can also do basic volume calculations. This does require the engineer or surveyor to create two DTM’s for comparison.
Support from your local dealer or supplier will be important consideration when buying a total station. On going support from them in the form of yearly checks or calibrations of your Total Station will be important. You need to look after your Total Station and know that it is consistently giving you the correct readings that will enable you to either engineer or survey your site with accuracy.
What accessories should I have with the Total Station?
Tripod. The tripod you get with your Total Station should be either wooden or of a composite construction, it should not be the aluminium type. The wooden tripods are less susceptible to the affects of thermal expansion during the course of the day and also provide a more stable support for the heavier Total Station. Make sure that your Tripod is looked after and use this test for a tripod to find out if it is in serviceable condition. If your Total Station doesn’t come with a tripod we would recommend a new wooden one.
Mini Prism. A mini prism is a really helpful accessory for a Total Station. It is very useful for the fine detail and accurate work that is done closer to the Total Station. Remember to select a mini prism that is from the same manufacturer as the Total Station.
Extra Long Detail or Prism Pole. This will probably be a nonstandard item for your Total Station. Most supplied detail poles will only have a maximum height of 2m to 2.5m. This can be restrictive if you have an undulating site, or one with lots of walls, or one with lots of traffic. Detail poles with a height capability of 4.65m are available, this would be more than adequate for any situation.
Thumb Release Bipod. A thumb release bipod is a very handy accessory for holding the detail or prism pole steady for those more accurate or longer readings. The bipod clamps to the detail or prism pole which can then be plumbed up and held in place by releasing your thumbs from the clamps.
Can I not hire a Total Station?
You can certainly hire a Total Station and that may well prove to be a valid option for you. The cost of buying a Total Station can be prohibitive, especially when you go for the more advanced Total Stations like the Robotic Total Station. A general rule of thumb that I use to decide whether to buy or hire a Total Station depends on the amount of time I would have the Total Station on hire for. My break point is around six months, so if I can foresee that I would need the Total Station for more than six months I would consider buying a New Total Station. For periods that I know I would be less than six months I would hire a Total Station rather than buy one.
Most large contractors in the UK only hire survey equipment for their sites and will never buy it outright. This is even if it is a long-term project. This is due to the way the construction projects are priced with the UK and the contractors consider that once all the costs should be borne by that particular project. There is also the advantage that if something goes wrong with the Total Station then all they need to do is request an exchange.
I’ve bought a Total Station, What now?
So, you have decided on the Total Station that best suits your needs and have taken delivery of it. Now you need to take care of it and ensure that it keeps giving the best results it can over its lifetime.
Record and securely store your Total Station’s Serial Number. The serial number should be on both the Total Station and the Calibration Certificate. There will also be serial numbers on some of the accessories that come with the Total Station. Taking photos is always helpful.
Make sure that you have insurance for your Total Station. Insurance should not only cover theft of the Total Station but also accidental damage, this is known as all risk insurance. Read these posts regarding survey equipment insurance and survey equipment insurance set to soar by over 300 percent. You should also consider new for old equipment cover. This will ensure that you will get a new Total Station if anything happens.
Never store your Total Station in the box if it is wet. This will damage your Total Station and corrode the internal circuits and components that comprise your Total Station. It is fine to transport the Total Station for short periods in the box if it is wet, but it is advisable to leave it in a safe location over night to dry out fully, ideally in a warm air draft.
Go out and use your Total Station and get a feel for what it can do. Try the new functions and maybe set out or survey things twice to get a feel for the accuracy you can achieve. As long as you know what it is capable of and if you look after it you should have years of accurate setting out or surveying with your Total Station.