Standard Prism On The Tripod

Which Prisms are Used in Land Surveying?

When it comes to land surveying, most total stations use purpose-built glass prism reflectors for the EDM signal. Usually, a typical total station has the capacity to measure a distance of up to 1,500 m (4,900 ft) with an accuracy of about 1.5 mm (0.059 in) ¬Ī 2 parts per million.

A prism is a corner cube or a reflector that comes attached to a surveying pole and is used as a target for distance measuring. They also include prism poles that are used to accurately measure the elevation of the existing ground by using a sight level that may include either a total station, a transit level, an automatic level, or a laser level.

Understanding Prism Constants and Offsets

A prisms constant is a property of a certain prism model that exists to define the relation of the distance measurement to the mechanical reference point of the prims. The prism constant is unvarying and should not have any influence on the measurement.

Most cube prims come with an offset due to the transmitted light beam that comes from the EDM. Due to these factors, it may take longer to enter and exit the prism. Common offsets that you will come across include 0, -17.5 mm, -30 mm, -34 mm, and -40 mm.

At the same time, land surveyors use a variety of different prisms that all come with their own unique properties and different characteristics.

360-Degree Prisms

360-degree prism works similarly to a round prism with the main difference being in it providing a permanent and continuous reflection of the EDM signal. Additionally, they are much easier to use once a pole operator needs to move quickly from one point to another. Omnidirectional prisms are the best choice when it comes to using stations that have automated target recognition, as they don’t need constant readjustments.

A 360-prism consists of six corner cubes that are joined together into one. This unique type of arrangement allows the measuring beam to reflect the beam directly back to its source from any position of the prism set. Thanks to the even distribution of the prism, it is capable of resulting in similar accuracy and a similar offset from any side. This type of reflector can be also used for all types of robotic work done with a surveying pole.

Explore the table below for a quick overview of the key information we've gathered to enhance your understanding of the topic about 360 degree prisms.

grz122 360 degree prism for leica total station  atp1 360 degree prism  vx&s trimble 3600 degree prism series 
Model GRZ122 ATP1 VX&S Series 
Brand Leica Sokkia Trimble
Height Offset 86.0mm 100.0mm 139.0mm
Offset - Constant -11.3mm 7.0mm 2.0mm
Leica Constant +23.1mm
Accuracy +/-2.0mm <5sec
Mount 12mm Leica Spigot

5/8''x11 Thread

5/8'' Thread

 

Mini Prisms

Mini prisms are capable of providing high positional accuracy due to their small size. They come with a built-in leveling bubble and an attachable spike. This type of arrangement allows for pinpoint accuracy during any type of land surveying job. Besides increasing the accuracy rate, they work well in decreasing the possibility of errors.

Mini prisms are also cheaper than other types of prisms and are good for multi-purpose usage as they perform well in short to mid-range measurements. Another very important advantage of mini prisms is owed to their size as they are quite easy to keep in storage and don’t cause any trouble in transportation.

Explore the table below for a quick overview of the key information we've gathered to enhance your understanding of the topic about mini prisms.

gmp111-0 leica mini prism 
mpr122 360 degree mini prism for leica total stations 
grz101 leica 360 degree prism for leica total stations 
Model
Brand
Leica
Leica
Leica
Height Offset
50.0mm
50.0mm
15.0mm
Offset - Constant
-34.4mm
-6.3mm
-4.40mm
Leica Constant
+17.5mm
+28.1mm
+30.0mm
Accuracy
+/-2.0mm
+/-2.0mm
+/-1.5mm
Mount
1/4'' Thread
5/8'' Thread
1/4'' Thread

 

Monitoring Prisms

Monitoring prisms are usually installed on structures like buildings, bridge piers, tunnel walls, pavements, or railroad tracks. Once changes in the positions of monitoring prisms are noticed, it indicates movements in the structures. These types of prisms are essential for tachymetric structural monitoring.

In order for the highest accuracy to be achieved, the prisms needs to be positioned in the center symmetrical point. These types of prisms also make it possible for a large number of measuring points to be observed so the object is measured economically and precisely within the varying requirements.

Explore the table below for a quick overview of the key information we've gathered to enhance your understanding of the topic about  monitoring prisms.

gmp111-0 leica mini prism 
mpr122 360 degree mini prism for leica total stations 
grz101 leica 360 degree prism for leica total stations 
Model
ADP109
Brand
Leica
Leica
JEOC
Height Offset
90.0mm
64.0mm
128.0mm
Offset - Constant
-25.0mm
-34.0mm
-15.0mm
Leica Constant
+8.9mm
+0.0mm
+19.4mm
Accuracy
+/-1.0mm
5arcsec
5arcsec
Mount
L-bar
5/8'' Thread
M8

 

Circular Prisms

Circular prisms are considered reflectors that are used to reflect the EDM beam from a total station. Full-size reference prisms are capable of providing great accuracy at high ranges and can also be used to calibrate a monitoring network. A standard prism also comes with <5 seconds, making it really accurate for high-range measuring.

Explore the table below for a quick overview of the key information we've gathered to enhance your understanding of the topic about standard circular prisms.

gph leica circular prism  gpr121 leica circular prism  gpr111 leica circular prism 
Model GPH1P GPR121 GPR111
Brand Leica Leica Leica
Height Offset 86.0mm 86.0mm 86.0mm
Offset -  Constant -34.4mm -34.4mm -34.4mm
Leica Constant +0.0mm +0.0mm +0.0mm
Accuracy +/-0.3mm +/-1.0mm +/-2.0mm
Mount 12mm Leica Spigot 12mm Leica Spigot 12mm Leica Spigot

 

Reflective Targets

Reflective targets help to provide measurements over long distances. These can be as simple as adhesive targets and as complex as pole-mounted target systems. Adhesive targets come with a reflective surface or a white and black reflective target pattern. They are very easy to use and can be attached to most surfaces and should be available in different sizes in order to accommodate different types of land measuring situations. We can't say that reflective targets are prisms, but they definitely provide a similar, and also very accurate measurement in the other hand.

In order to suit various types of monitoring situations, reflective targets need to come in a variety of colors, so they can be visible during daylight or in various types of conditions.

Explore the table below for a quick overview of the key information we've gathered to enhance your understanding of the topic about reflective targets.

gmp111-0 leica mini prism 
mpr122 360 degree mini prism for leica total stations 
grz101 leica 360 degree prism for leica total stations 
Model
TR01
Brand
Metricop
Metricop
Metricop
Dimension 
40x40mm
10x10mm
to 60x60mm
R - 60mm
H - 86mm
Distance 
10-150m
10-150m
10-150m
Mount
√ė 6mm
Self -Adhesive
M8
Color
Yellow
Silver
Yellow
Material
Delrin - Plastic
Delrin
Delrin - Plastic

 

Conclusion

In land surveying, various prisms are employed to ensure accurate measurements and monitoring. From 360-degree prisms that provide omnidirectional reflection to mini prisms that offer high positional accuracy, surveyors have a range of options to choose from. Monitoring prisms are essential for structural monitoring, while circular prisms excel in high-range measurements. Reflective targets, while not prisms, also contribute to the accuracy of measurements over long distances. Understanding the different types of prisms and their applications is crucial for choosing the appropriate tools for any land surveying project.

To learn more about land surveying, you can explore the following resources:

These articles will provide you with additional information on land surveying techniques, equipment, and applications in various contexts.

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