Mini Prisms: The Basics and Benefits

By Chris Doohan on 4th January 2024 (updated: 1st May 2024) in News

mini prisms

The mini prism is all about precision. Ideal for a range of surveying applications, the mini prism cuts through the complex, offering a straightforward solution for achieving reliable results.

At SEP, we supply a range of prisms for use in land surveying and construction, alongside tools and accessories that enhance the process. Our experience and trade relationships with leading manufacturers means we can offer the best to our customers. No matter what you’re looking for, we have a prism,mini prism pole, or adaptor to guide your surveying.

In this post we’ll cover the basics and benefits of using mini prisms in land surveying. From their features and benefits, how they differ from similar products and a short how-to guide on setting up a mini prism with your total station. Read on to learn more from SEP.

 

What is a Mini Prism?

A mini prism is a small optical device used in surveying and geodetic measurements. It typically consists of a prism enclosed in a compact housing with a mounting thread, allowing it to be easily attached to surveying instruments such as total stations or levelling rods.

Mini prisms reflect and redirect a surveying instrument’s laser beam, allowing for accurate distance and angle measurements in the field. They’re handy tools for precise surveying work in various applications, enhancing measurements’ accuracy over longer distances.

How do they differ from similar products?

While not directly similar to prisms, GPS receivers are commonly used in surveying for precise positioning. They provide real-time data and can complement traditional surveying methods.

Whereas, reflective targets are flat or dome-shaped, with reflective coatings and serve the same purpose as prisms by reflecting surveying instrument signals, but they don’t have the same angular accuracy as prisms.

How do Mini Prisms benefit surveying applications?

Mini prisms offer several benefits from accuracy and range to field efficiency and time saving. They allow surveyors to work over longer distances without sacrificing accuracy. The reflective properties of prisms enable surveying instruments to “see” the target even at a considerable distance.

They’re also compact and lightweight, making them easy to transport and mount on various surveying instruments. They can be attached to total stations, theodolites, or levelling rods, providing flexibility in different surveying scenarios. In some cases, accessing survey points in challenging terrain or environmentally sensitive areas may be impractical or environmentally damaging. Mini prisms allow surveyors to collect data without disturbing the surroundings.

Using mini prisms can streamline surveying operations by reducing the need for physical access to certain points. Surveyors can set up instruments in more convenient locations while still obtaining accurate measurements through the reflective properties of the prisms.

The use of mini prisms can save time in the field by eliminating the need for surveyors to physically occupy every point. This is especially beneficial in large-scale surveys where efficiency is crucial.

mini prism

How to Use Mini Prisms in Surveying

By following these steps, you can effectively use mini prisms in surveying to obtain accurate and reliable measurements for your project.

Materials Needed:

  • Mini prism with mounting thread
  • Surveying instrument (total station, theodolite, or similar)
  • Surveying pole or rod
  • Tribrach
  • Prism adapter (if required)
  • Levelling tools (if necessary)

Setting Up:

Choose a suitable location for your surveying instrument, ensuring it has a clear line of sight to the area you want to survey. Level the instrument using the built-in levelling bubble or other levelling tools. Place the tribrach on the instrument’s base or mounting plate. Lock the tribrach in place to secure the instrument.

Ensure the mini prism has a mounting thread compatible with your instrument. If not, use a prism adapter to make it compatible. Screw the mini prism onto the mounting thread of the instrument or the prism adapter.

Choose a surveying pole or rod of appropriate height for your survey and attach the mini prism to the surveying pole using the mounting thread or a specialised prism holder.

Taking Measurements:

Position the pole at the point you want to survey, making sure it is stable and firmly planted. Adjust the height of the pole if necessary, ensuring the mini prism is at the desired surveying height.

Look through the surveying instrument’s eyepiece or viewfinder and use the instrument’s controls to aim the laser or measurement beam at the mini prism on the surveying pole.

Adjust the instrument’s controls to centre the crosshairs or reticle on the mini prism and ensure that the instrument’s display shows a stable and accurate measurement.

Once the mini prism is accurately targeted, record the distance and angle measurements provided by the instrument. Take multiple readings for increased accuracy, especially over longer distances.

If surveying multiple points, repeat the process by moving the surveying pole to the next location. Continue the surveying process, ensuring accurate measurements at each point.

Document the recorded measurements along with any relevant notes. Use the collected data for mapping, analysis, or other surveying applications.

Extra Tips:

  • Calibrate your instrument and mini prism before starting the survey to ensure accurate measurements.
  • Check for any obstructions or reflective surfaces that may interfere with measurements.
  • Be mindful of environmental conditions, such as wind or vibrations, that could affect the stability of the surveying pole.

What Mini Prisms do SEP stock?

We stock a range of mini prisms, from L-bar to nodal and sets including prism poles. In addition, we also have a selection of mini prism accessories to make life easier for you on-site. These include quick change adapters, as well as prism pole attachments and sets, manufactured by some of the surveying industry’s biggest names.

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What is the difference between a 360 Prism and a Mini Prism?

Mini prisms are compact and designed for accuracy over shorter distances, while 360-degree prisms are larger and provide reflection in all directions, making them suitable for applications requiring a broader field of view. The choice between the two depends on the specific requirements of the surveying task at hand.

360 prisms are ideal for applications such as monitoring large construction sites, machine control, or any scenario where the surveying instrument needs to capture signals from all directions. Whereas mini prisms are perfect for tasks like construction layout, monitoring, and other applications where a compact and portable solution is needed.

What is the difference between Active Lock and Passive?

Active Lock and Passive refer to two different methods of target acquisition and tracking in surveying instruments, particularly in total stations. Let’s break down the differences:

Active Lock

Active Lock, also known as target tracking or continuous tracking, involves the surveying instrument actively adjusting and following the target in real time. The total station emits a continuous laser or infrared beam towards the target. The instrument continuously adjusts its orientation to keep the laser or infrared beam locked onto the target.

Active Lock is useful when surveying moving objects or when the target is subject to vibrations or environmental changes. It provides real-time tracking capabilities, ensuring that measurements are constantly updated.

Commonly used in applications such as monitoring dynamic structures, machine control, or any scenario where the target is in motion.

Passive

Passive target acquisition relies on a reflective target that reflects the incoming surveying instrument signal (usually a laser beam). The total station emits a laser beam towards a passive target, and the instrument detects the reflected signal from the target.

Once the signal is detected, the instrument measures the distance and angle to the target.

Passive mode is suitable for static or slow-moving targets. It’s often more straightforward to set up since it doesn’t require constant adjustments like Active Lock.

Commonly used in standard surveying applications, construction layouts, and other scenarios where the target is relatively stationary.

Choosing Between Active Lock and Passive

Though there are many applications for mini prisms, the two lock options have their advantages and disadvantages when it comes to each use case.

It’s best to choose Active Lock for moving targets or situations where the target experiences dynamic changes and Passive for stationary or slow-moving targets. Consider the specific requirements of your surveying task. Active Lock may be overkill for static measurements, while passive may not be suitable for tracking moving objects.

Active Lock can also require more initial setup and calibration due to its continuous tracking nature, whereas Passive is often simpler to set up, especially for standard surveying tasks.

In summary, the choice between Active Lock and Passive depends on the nature of the target, the specific requirements of the surveying task, and the ease of setup needed for the application.

Learn the easiest way to make sure your total station locks onto the correct prism everytime with this informative tutorial from Leica.

SEP Are Here to Help

Understanding your tools and the best ways to use them is paramount to successful surveying. SEP are here to guide you in kitting your team with the correct tools needed for the job, and when projects are short-term, we offer surveying tools for hire too. If you’re stuck on the right tool for the job, speak to one of our specialists and we’ll offer only the best advice when it comes to quality surveying practices.