Mini Prisms: The Basics and Benefits

Mini prisms serve an essential purpose in modern surveying by improving precision and versatility. These prisms are compact and highly durable, making them ideal for a range of surveying applications, including land surveying and construction.

Mini prisms help surveyors capture reliable data even in challenging conditions, serving as valuable accessories to support a variety of projects. Our range includes poles, adaptors, and other prisms from leading manufacturers.

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.

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.

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.

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 Process for Mini Prisms:

1. Choose a suitable location for your surveying instrument, ensuring it has a clear line of sight to the area you want to survey.
2. Level the instrument using the built-in levelling bubble or other levelling tools.
3. 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.
4. Screw the mini prism onto the mounting thread of the instrument or the prism adapter.
5. 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.

It’s often best to document your notes with the recorded measurements to help when they’re being referred back to later. Nowadays, you can typically make notes in the controller to be saved alongside the appropriate datasets for easy analysis back in the office. Prism data can be used for mapping, analysis, or other surveying applications.

Extra Tips for Using Mini Prisms:

• 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.

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 leading surveying industry brands.

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.

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.

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.

Unsure which kinds of prisms will best support your current workflows? 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.

Every member of our sales team has years of experience working with survey equipment on a variety of different sites. We’ve seen firsthand just how impactful the addition of mini prisms, 360° prisms, monitoring prisms, and reflective targets can be when using total stations. Although prisms aren’t as costly as other survey instruments, it’s important to choose the right ones to avoid clutter in your workshop. Get in touch today.