Understanding Survey – UTS vs GPS
This article was crafted in collaboration with Steve Chambers. With close to two decades of experience in construction surveying, Steve now oversees the survey requirements across a diverse portfolio of projects in his role as Survey Manager for CMC. His fervent advocacy for the surveying profession and his expertise in the latest surveying technologies make him an invaluable contributor to the depth and quality of EngiMBA’s articles.
“Survey is one of the most important elements of building something in construction. In fact, I could be convinced that it is the most important.”
So why then is it that most Engineers can go almost their entire career without understanding how survey works?
In short, the answer to that question is, Good Surveyors. A good surveyor sorts it all out, handles the issues and gives us the nice report with all green numbers that we can put in our lot. If the numbers are green, we don’t need to know much more. However, the issue is that our industries competent Surveyors have produced incompetent Engineers because surveyors are often times too busy to take the time to mentor young engineers.
So the aim of this series of blogs, is to lay out some fundamentals of survey.
The fundamental here is accuracy, Like many things with surveying , it comes down to the required accuracy of the given task.
Universal Total Stations (UTS)
Purpose:
UTS instruments are commonly used in construction and civil engineering for precise 3D positioning.
They track a target (mounted on a machine, with an array of sensors to calculate the relative position of the blade to the design) to determine accurate coordinates in three dimensions.
Technology:
UTS relies on active target technology to lock onto and track the intended target. This means it is limited by line of sight to the instrument and that the further you are away from the instrument the less accurate the resulting works
It provides millimeter precision on the work site.
Advantages:
More accurate and versatile than GPS (More accurately it is actually GNSS) solutions.
Opposed the GPS (GNSS) which relies on relative unobstructed view of the sky (satellites) UTS required line-of-site between the instrument and working machines prism, The instrument need to be in a stable position free of vibration and need to be in sighting view and distance of an established survey control network points for correct positioning and orientation.
GPS (Global Positioning System) or GNSS (Global Navigation Satellite System)
When people refer to GPS, they usually mean GNSS. GPS (Global Positioning System) is a satellite-based navigation system developed by the United States, while GNSS (Global Navigation Satellite System) is a broader term that encompasses all satellite navigation systems, including GPS, Russia's GLONASS, Europe's Galileo, and China's BeiDou. Essentially, GPS is a specific system within the larger GNSS framework.
Overview:
It’s used in mgnssobile phones, in-car navigation, search and rescue equipment, and more. However, survey grade GNSS utilise a second high grade GNSS receiver in a fixed location within a certain range of the project to offer a " Correction signal" to achieve centremetre level regional positioning.
Surveying with GPS:
GPS provides direct position information (latitude, longitude, and height) without measuring angles (it measures distance from the satellites).
Survey control can be established almost anywhere with a clear view of the sky for satellite signal reception.
Modern GNSS receivers often utilize multiple satellite systems (such as GPS, Glonass, BeiDou, and Galileo) to improve reliability and accuracy.
Geodetic GPS Receivers:
Survey-grade GNSS receivers use two frequencies broadcast by GNSS satellites.
GPS Baseline:
A GPS baseline involves two survey-quality GPS receivers placed at each end of the measured line.
Simultaneous observations from the same GPS satellites yield accurate baseline measurements.
In summary, UTS provides high precision on construction sites, while GPS offers broader applicability and convenience in everyday scenarios. Surveyors often choose the right tool based on project requirements and environmental conditions21.
Bonus; Australian Survey Slang
Here are some common slang terms used when referring to survey equipment
Total Station: Often referred to as a "gun" or "robot," this is a key piece of equipment for precise measurements. Robotic total stations are often call a “Jigger”
Theodolite: Sometimes called a "theo" or "scope," used for measuring horizontal and vertical angles.
GPS Rover: Known as a "rover" or "stick," this is used for satellite-based measurements.
Level: Often called a "dumpy" or "leveler," used for establishing a horizontal plane.
Prism: Referred to as a "target" or "reflector," used with total stations for distance measurements.
