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A Complete Guide to High-Accuracy Measurements in Disconnected GNSS Environments

We’ve all experienced a frustrating lack of signal service when working in the middle of a city or under dense canopies, making us wonder how in our tech-driven world. The past few decades we’ve seen technological innovation skyrocket, giving us our most connected and advanced world modifying how we live, work, and communicate with one another.  We haven’t conquered the technological sphere by any means, and the past few decades of innovation have provided us with a vision of what we can become. Maximizing outputs, completing tasks quicker, and increased safety are some of the main driving factors that are provoking the geospatial industries to advance farther. For surveying professionals, it was the demand for engineered devices that let users achieve centimeter-accuracy in Global Navigation Satellite System (GNSS) impaired environments: driving top industry experts to develop a sophisticated solution.

GNSS is one of four satellite positioning systems. You likely have heard of the Global Positioning System (GPS), but there are some satellite systems that may not be so familiar, like BeiDou Navigation Satellite System (BDS) and Galileo. Each one of these acronyms embodies a specific group of artificial satellites that send position and timing data from their orbit by firing two carrier waves (L1 and L2) of information between Earth and satellite. The user’s antenna receives the signal and the processing unit makes sense of it. In addition to these four satellite systems there are a collection of satellite constellations orbiting around the Earth’s surface continuously transmitting signals. Collectively working together, these satellites are positioning us to become an autonomous geospatial world, with GNSS positioning itself to be the world’s new GPS. Whether we are looking to construct new buildings, provide more telecommunications for our 5G future, or to simply find where we are going when we get lost, GNSS is paving the way for us to get there.

Also Read: 5G and geospatial will together power future cities

The shift from GPS to GNSS is accuracy, redundancy, and availability. Users who integrate GNSS receivers into their workflow have their position triangulated by grabbing at least four satellite signals.  While satellites rarely fail, if one did, your GNSS receiver would pick up another signal from another system.

With this global coverage, how do we lose our GNSS connectivity? GNSS satellite signals can be compared to a 50-watt lightbulb. They emit low frequencies making their signal easily interruptible. The signal needs a clear line of sight to the satellite it is tracking, if the line of sight to a satellite is blocked by objects such as buildings, trees, and/or bridges, the receiver cannot receive direct signals from that satellite.  In other cases, the signal is reflected off an obstruction which causes a time delay and therefore a loss of accuracy. In locations that have a lot of obstructions, such as the downtown area of a large city, they can block so many satellites that the receiver cannot accurately calculate its position. 

Regulatory requirements on spatial data accuracy and real-time high-accuracy GNSS positioning are gaining ground.  Within some industries, only the utmost precision is acceptable. While highly accurate horizontal and vertical data can be achieved in some areas, achieving centimeter-level accuracy in heavily obstructed environments created an industry demand for a solution.

Measurements in Disconnected GNSS Environments

The Power of Three

Before laser offset mapping was introduced, capturing high-accuracy 3D measurements for hard-to-reach assets required extensive training and expertise. Crews needed to use a total station that required a different software workflow and then mesh the data back in the office.  Capturing assets was a tedious and time-consuming process that triggered clumsy and inefficient workflows. 

The collaboration of Eos® Arrow® Series Receiver, Esri® Collector® for ArcGIS®, and LTI’s laser rangefinders is transforming how crews shoot, capture, and share high-accuracy 3D location data in GNSS-impaired environments.  Users now receive RTK-Level accuracy without ever needing to leave the Collector/AGOL (ArcGIS Online) environment: achieving a highly efficient and streamlined workflow.

ALSO READ: How GNSS works?

GNSS Receiver Integration

A GPS receiver is designed to compute the locations of its antenna. This means to capture a feature’s location the user must occupy that location.  In some situations, that location isn’t safe for field crews to occupy.

Field Data Collection Software

Having the right high-precision GNSS mobile GIS software that utilizes your GPS or GNSS receiver when performing your field data collection will let you seamlessly collect, process, and share high-accuracy data.

Measurements in Disconnected GNSS Environments

Laser Rangefinder Integration

Offset information can be estimated or obtained more accurately when using a laser positioning system. Integrating a laser range finder and an electronic compass (providing distance, inclination, and azimuth) with your GPS/GNSS receiver you can significantly reduce travel time associated with field data collection.

So, what is an offset?

An offset is the combination of a distance and a direction. Combining a recorded GPS position with the associated distance and direction to your object ensures high-accuracy positioning data. In the setting of GNSS, an offset is used to define a shift from one location to another. Data measured with the laser is in three dimensions to incorporate any differences in elevation.

Applying offsets to features by recording both a GNSS position and associated distance and direction to the object of interest is very useful in challenging situations. Say you wish to record the attributes of a power pole that is on the other side of a steep, narrow ravine, rather than risking injury climbing across the ravine you can use the offset capability to stand at one side of the ravine and simply record the offset to the pole on the other side. In fact, the offset function allows the user to stay at one location and record the offsets and attributes of all features within sight before moving to the next location to do the same.

Measurements in Disconnected GNSS Environments
Range-Range Intersect
Measurements in Disconnected GNSS Environments

Users have three options for collecting high-accuracy measurements. Range-range requires two measurements to log each point, using the geometry of a triangle to calculate each coordinate. This method requires only a laser rangefinder, making this laser mapping offset the most cost-effective. Range-range is great for collecting geo-location-based information and mapping electric utilities.

Range-azimuth is another measurement method where the user pivots around their origin point while shooting to any feature in view. Most commonly used in urban forest mapping, wetland delineation, street furniture mapping, and sign and signal inventory. The only downfall to this routine is magnetic objects near your site may compromise the accuracy of your measurements.  

The final laser mapping offset technique is range-backsight. The user finds a safe location, records their position, aim and shoot feature, then manually enter the lasers value. This routine has been very beneficial for water, sewer, drain facilities, and pipeline right-a-way applications.

Laser mapping offset routines can be used for just about any application from mining, GIS, narrow ravines, mapping features on private properties, but most importantly, crews no longer need to occupy high-risk areas to collect a measurement.

The world’s GNSS mapping systems are entering a phase of transformation, indicting a massive paradigm shift within the GIS industry and how surveyors collect field data. High-accuracy positioning tools have become more advanced and affordable than ever before but faced limitations when found in a GNSS impaired environment. Unfortunately, mapping professionals do not have the luxury to map online in high signal-strength areas, and most of the time, projects that need GNSS mapping are not in GNSS-friendly, or safe environments. 

Creating a more streamlined, efficient, and safer user experience is what drove this collaboration between Eos, Esri, and LTI: to bring professionals a solution that would help solve a problem. This solution has created a more transparent workflow, and seamless integration between various software and hardware, by allowing users to Bring Your Own Device (BYOD) where data collection can be done on your smartphone or tablet.

Technology is truly transforming how we communicate and function. Consumer problems create a landscape for technological innovation and better user experiences.  Everyday, we continue to fulfill more duties while being expected to complete our objectives quicker.  With the help of intelligent high-tech solutions, we can do more in less time, we can be safer in our environment, and we can achieve better, more accurate results.  By cultivating a collaborative environment, Eos, Esri, and LTI have produced a new solution that does just that.