How is GNSS Used in Land Surveying and Mapping?

GNSS technology plays a significant role in land surveying and mapping, here we explore the technology and the various GNSS techniques surveyors use.

Land surveying is the science of marking boundaries, lines and perimeters of property and land using measured data. Land surveys are used for a range of purposes, one of the main goals of a land survey is to prevent legal land disputes arising and to correctly divide up territory. Land surveys are also used to assess a site’s usability for construction. 

GNSS – or Global Navigation Satellite System – is a constellation of satellites which transmit positioning data to receivers, providing surveyors with accurate location data, often to a high degree of accuracy. 

GNSS therefore plays a substantial role in both land surveying and mapping. Below we’ll discuss the main GNSS equipment used in surveying, the various GNSS techniques surveyors use, as well as which types of software are typically integrated with GNSS to paint a complete picture. 

Survey-Grade GNSS Equipment 

Here are some of the essential survey-grade GNSS equipment used in geospatial professions such as surveying and mapping, with recommendations for some of the best products on the market.

GNSS Receivers

GNSS receivers are integral to satellite positioning. They’re involved in converting signals from satellites into geographic positions. They work with various satellite systems, including GPS and Galileo. 

A high-quality example of a GNSS receiver is the Trimble R12 which performs to a high standard, even in unfavourable conditions. The Trimble R12i offers the additional feature of Trimble TIP Tilt Compensation Technology, which provides accurate measuring points without needing to precisely level the pole.

Other Trimble GNSS receivers include the Trimble R2 (which is also suitable for GIS mapping) and the handheld Trimble R1, which is specifically designed for mobile use. 

GNSS Antennas

GNSS is able to transmit navigation information via radio-frequency (RF) waves – and these waves are received by GNSS antennas. There are various different antenna types, with different cabling, connectors and accessories. 

An example of a high quality antenna is the Trimble ZEPHYR 3, a geodetic base antenna that uses the Trimble Stealth Ground Plate to function optimally in areas with high multi-path interference.

GNSS Processing and Correction Services 

These are a range of products which aim to make positioning information more accurate. 

Correction services allow surveyors to receive data which can help them position their GNSS receivers optimally. GNSS processing, meanwhile, helps surveyors to take more accurate measurements by cross-examining them with data from other reference points. 

GNSS Surveying Techniques and Methods

How do surveyors use GNSS to collect data? Well, that’s entirely dependent on the surveying techniques they use. Below are the three main methods of GNSS measurement used by surveyors.

Static Surveys

This technique is used to establish accurate coordinates for survey points. 

It records GNSS readings over time and processes the data to determine the most accurate result. In practice, this involves using two GNSS receivers placed at opposite points of a line. 

The receivers collect GNSS data at the same time over a duration of at least 20 minutes (although often longer). Once the data has been collected, software is used to determine the positional difference between both receivers.

The advantage of this technique is that it’s easy to perform and can provide very useful and accurate information. A disadvantage, however, is that it can often be a time-consuming process.

Real-time Kinematic Surveys

Sometimes shortened to RTK, Real-Time Kinematic surveys involve measuring distances at two points with two different receivers. 

However, the difference is that rather than keeping both points static, the first remains at baseline location while the other takes readings at different points across a distance of 20km. Once the process is completed, the data is processed. 

Like the static method, the accuracy of this technique remains high, however due to it being limited to a 20km distance, it is mainly used for quickly gathering data on small terrains and has limited use for larger areas. 

Post-processing Surveys

With post-processing, data from one or several GNSS receivers is processed. It involves taking large yields of data, rather than over a fixed period of time as with static and kinematic surveys. It’s often used for aerial applications and can be used to collect data over large areas.

A perk of post-processing surveys is their flexibility, as it can involve both stationary and moving base stations.Often post-processing software can also integrate with other applications and can usually run on a number of computers and devices.

Data Collection and Processing

Collecting and processing GNSS data as a surveyor involves having in your possession a number of software solutions and equipment. The essentials are: a data collection device, a data collection app and a GNSS receiver. 

When it comes to your data collection device, there are a range of options. We’ve found that most users tend to favour either an Android-based handheld device such as the Trimble TDC150, or a Windows-based table such as the Trimble T100 as they offer high performance and more flexibility when it comes to collaboration and connecting with other devices in the field. 

Data collection apps, meanwhile, fall into three distinct categories: cloud-based, standalone and HTML5. The most popular of which is cloud-based as it allows you to access your data from any device at any point, and every collaborator sees the same data  – so long as you have an internet connection (although it may have offline options too). 

A GNSS receiver is also essential for converting signals from satellites into geographic positions.

Other GNSS data collection software and practices include:

  • Data logger – a device that monitors and logs changes in conditions over time. They use a microprocessor, internal memory storage and a sensor to collect data.
  • Data Transfer – Data transfer involves first taking data from its source, called extraction, and then transmitting it to a new destination, called loading. This can be done manually or automatically.
  • Data processing –  Using software, surveyors can run analysis and gain insights into their collected data. This can help improve efficiency, productivity and limit errors.  

Integrating GNSS Data with Other Mapping Technologies

GNSS data can be integrated with other mapping technologies such as LiDAR and photogrammetry to create multiple source data sets for accurate and detailed maps.

LiDAR – or Light Detection and Ranging – is a technique for acquiring 3D information about the Earth’s shape and surface. It does this using a pulsed laser to determine variable distances to the Earth from a specific point. 

LiDAR allows professionals to visualise both natural and manmade terrains with accurate measurements. Its limitations however, include the fact that it tends to give a clear overview of a shape, but lacks contextual detail. However, this can be remedied when used in conjunction with GNSS and/or photogrammetry.

Photogrammetry refers to a specific technique of extracting 3D information from 2D photographs. It involves overlapping photographs of land or structures to build a 3D digital model. 

Due to its reliance on photography, weather conditions can easily affect the image quality and therefore the overall accuracy of the 3D models. However, this is why architects and surveyors partner the technique with LiDAR and GNSS systems to create a fuller, more detailed and accurate picture.

Elevating Mapping & Surveying with GNSS

Generating accurate land surveys and maps involves determining the boundaries of land ownership and pinpointing locations so that properties can be built and land disputes avoided. 

Naturally, the integrity of the profession depends on the accuracy of the measurements and data collected, which is why GNSS is so crucial. 

Using satellites to monitor the Earth’s topography helps ensure measurements are correct and precise. But it is when GNSS is integrated with other valuable surveying and data processing software, as well as used in harmony with established techniques and methods, that it really shines and proves its value to surveyors.

At KOREC Group, we cater to professionals in the surveying, geospatial, engineering and construction industries. We make it our mission to ensure any surveying or mapping task you undertake is done efficiently and effectively.

Check out our range of GNSS products to find the right equipment for your needs. Prefer to hire than buy? Our fully supported survey equipment hire service may be what you need, just give us a call to see how we can help you.