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GPS vs GNSS: Unraveling the Geospatial Navigation Revolution in Surveying

GPS v GNSS

GPS and GNSS

In the realm of surveying and geospatial data collection, two acronyms are regularly used interchangeably: GPS (Global Positioning System) and GNSS (Global Navigation Satellite System). Although used interchangeably and are related to one another, they mean vastly different things. 

These technologies have revolutionized the way surveyors gather precise location data, enabling unparalleled accuracy and efficiency in applications such as land surveying, construction, agriculture, monitoring and more. These systems are generally used to determine location and timing. 

This article delves into the differences between GPS and GNSS, exploring their respective functionalities, advantages, and implications for modern surveying practices. GNSS systems can change the way you practice surveying.

Hemisphere S631 being used to survey

What Came First GPS or GNSS?

GPS (Global Positioning System): The Pioneer in Navigation

The Global Positioning System, developed and maintained by the United States Government, was the first of the satellite navigation systems. Originally, it was only available for military use. Although it wasn’t clear at first, this was to revolutionize surveying. 

Launched in the late 1970s, GPS consists of a constellation of satellites orbiting the Earth, transmitting precise signals to receivers on the ground. These signals contain information about satellite positions, precise timing, and other relevant data.

GPS relies on the transmission of signals from satellites to ground based receivers. By computing the distances to multiple satellites simultaneously, GPS receivers can pinpoint their exact location accurately.

GPS and Global Coverage

In its current form, the GPS system consists of 24 GPS satellites in orbit around the Earth. These satellites are spread across six orbital planes and are arranged so that a gps receiver can always “see” or receive signals from at least 4 different satellites at any time. With at least four satellites gps positioning system can determine location.

These satellites provide global coverage allowing for real-time positioning and timing around the world. These signals are used in everything from surveying, to military use, to autonomous vehicle navigation, marine navigation and more.

A dual frequency hemisphere s320

GNSS (Global Navigation Satellite System): The Global Evolution

GNSS, on the other hand, stands for Global Navigation Satellite System. While GPS is the most well-known, GNSS is an umbrella term that encompasses all global satellite-based navigation systems, including GPS (the Americans), GLONASS (the Russians), Galileo (the European Unions), BeiDou (the Chinese), and others.

The evolution of GNSS began with the launch of GLONASS in the 1980s, followed by Galileo and BeiDou in the early 2000s. Each system is made up of its own constellation of satellites, transmitting signals that can be received by compatible receivers worldwide. This interoperability between systems has significantly improved the accuracy and reliability of positioning data.

GNSS and Global Coverage

GNSS satellite constellations generally provide global coverage. Of the 4 mentioned above, they all provide global coverage. However, two of the other systems are regional systems. These include the Japanese QZSS and the Indian IRNSS systems, both regional to their respective countries. 

Generally, when a country launches their own satellite navigation system they being with a regional system before deploying it as a global satellite positioning systems.

What is the Difference in Accuracy?

In the early days, GPS alone provided relatively good accuracy for surveying purposes. However, with the establishment of GNSS and the integration of multiple systems, the accuracy has improved dramatically. 

GNSS enables surveyors to access a greater number of satellites from different constellations simultaneously, resulting in improved precision and redundancy. GPS systems, those that can only receive signals from GPS satellites are at a significant disadvantage when compared to GNSS systems.

Today, high-precision GNSS receivers can achieve centimeter-level accuracy, critical for surveying applications such as boundary determination, construction layout, and topographic mapping. The widespread adoption of GNSS has heralded a new era in surveying, where rapid data collection and high-level accuracy have become the norm.

Availability and Reliability

One of the significant advantages of GNSS over GPS alone is its enhanced availability and reliability. By integrating multiple satellite systems, GNSS receivers have access to a more satellites. This means that even in challenging environments such as dense urban areas, valleys, or under foliage, GNSS receivers can maintain lock on satellites, ensuring uninterrupted data collection. In short, the more data available, through more satellites, the better chance the receiver has to obtain a solution.

Moreover, in situations where obstructions momentarily block signals from one constellation, receivers can rely on signals from other constellations to maintain continuous positioning. The increased redundancy offered by GNSS has made surveying operations more efficient and productive, as surveyors are no longer confined by the limitations of a single system. 

Traditionally, GNSS receivers have first obtained a fixed solution on GPS, and then brought in satellites from other constellations to enhance their position and accuracy. However, in many 7th generation receivers, like the Hemisphere S631, the receiver can obtain a fixed solution from any constellation and use the one with the best possible signal strength and clarity.

S631 in trees

Who Fixes Faster?

Time to First Fix is the time it takes for a receiver to acquire enough satellite signals to calculate its position accurately. In this aspect, GNSS outperforms GPS alone. Since GNSS receivers can access signals from multiple satellite systems, they can achieve faster fix times even in challenging environments. 

This reduced fixed time translates to quicker surveying times, even in difficult environments. However, not all receivers are able to perform an initial fix on all constellations. Check out the below video on comparing 7th generation and 6th generation technology.

The fix time of a GNSS system is also dependant on the processing engine on the receiver. Environments like buildings and trees increase the multi path interference, which can increase fix times. 

What is the Cost?

Historically, GPS technology has been expensive, particularly for high-precision applications. However, the advent of GNSS has introduced more cost-effective options. As the number of satellites in different constellations has increased, the variety of GNSS receivers available in the market has expanded, catering to different budgetary requirements.

While specialized high-precision GNSS equipment can still be costly, there are more affordable options that offer reasonable accuracy for various surveying tasks. This accessibility has made GNSS technology more attractive to a broader range of professionals and industries. With the advent of 7th generation of GNSS technology coming soon, even more cost effective and reliable receivers will become available.

Increasing Accuracy

Both GPS and GNSS benefit from augmentation systems, which provide additional correction data to enhance positioning accuracy further. Augmentation systems include WAAS (Wide Area Augmentation System) for GPS and EGNOS (European Geostationary Navigation Overlay Service) for Galileo, among others. These systems broadcast correction signals to GNSS receivers, compensating for atmospheric disturbances and other error sources. Often times, geostationary satellites are used in order to provide better coverage, but this means it is only available in specific regions. 

These systems are particularly valuable in high-precision surveying, where centimetre-level accuracy is essential. By improving the reliability and accuracy of GNSS measurements, this contributes to the growing precision of modern positioning. 

Hemisphere machine control on an excavator

Conclusions

In conclusion, GPS and GNSS have revolutionized the surveying industry by providing accurate, reliable, and accessible positioning data. While GPS was the pioneering technology that laid the groundwork for satellite-based navigation, GNSS has emerged as a powerful evolution that integrates multiple global systems. GNSS offers greater accuracy, availability, and reliability due to its ability to access signals from different constellations simultaneously.

Surveyors now have access to a wide range of GNSS receivers, offering diverse accuracy levels to suit various budgetary constraints and application requirements. As GNSS technology continues to advance, surveying professionals can expect even higher levels of precision and efficiency in their geospatial data collection endeavors, driving progress in various industries and shaping our understanding of the world around us.

Bench Mark Equipment & Supplies is your team to trust with all your surveying equipment. We have been providing high-quality surveying equipment to land surveyors, engineers, construction, airborne and resource professionals since 2002. This helps establish ourselves as the go-to team in Calgary, Canada, and the USA. Plus, we provide a wide selection of equipment, including global navigation satellite systems, RTK GPS equipment, GNSS receivers, and more. We strive to provide the highest level of customer care and service for everyone. To speak to one of our team today, call us at 403-286-0333 or email us at [email protected] 

About the Author

Nolan has been working in the surveying field since 2017, starting as a part-time student at Bench-Mark while attending the University of Calgary. He now works in technical support and sales helping customers find the right product for them.

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