Surveypod - Blog #surveying

How many Satellites and Channels require in your DGNSS?

Tue, 10 Jun 2025 11:03:37 +0000

In the realm of precision navigation and positioning, Differential GNSS (DGNSS) often emerges as a critical yet misunderstood technology. Despite its pivotal role in enhancing GPS accuracy, several myths persist, clouding its true value. Today, let’s discuss some common misconception in the survey world related to DGNSS (or DGPS).

You may have heard people emphasize the importance of having 400, 800, or even 1200 channels in a DGNSS receiver. Have you ever thought deeper to understand what this actually means? Let’s clarify this with some simple mathematical calculations.

There are a total of 120 operational satellites: GPS (31), Galileo (24), GLONASS (24), BeiDou (30), NavIC (7), and QZSS (4). These satellites are distributed across the orbital plane and are not all visible from a particular point on Earth.

What is an Elevation Mask?

An elevation mask is a threshold angle that defines the minimum elevation above the horizon that a satellite must have to be considered in the positioning calculations of a DGNSS receiver. The purpose of this mask is to filter out low-angle satellite signals that are more likely to be degraded by atmospheric interference, multipath effects, and obstructions.

What value to keep for Elevation Mask?

It is recommended to set the Elevation Mask to 15 degrees to use only high-quality satellites for positioning. However, even with an Elevation Mask set to 5 degrees, you wouldn’t be able to see even half of the satellites simultaneously.

How many satellites with Elevation Mask as 5 degrees?

With an Elevation Mask of 5 degrees, you would only be able to track a maximum of 14 GPS, 6 Galileo, 6 GLONASS, 11 BeiDou, and 4 QZSS satellites. Out of the 7 NavIC satellites, only 5 are operational, and many companies do not support NavIC.

So how many Channels?

Now, let’s talk about channels. The L1 and L2 bands require only one channel each, whereas the L5 band requires two channels. Interestingly, out of the 120 satellites, only 40–45 have L5 bands.

Here’s the mathematical calculation with a 5-degree Elevation Mask (in general, if you set it to 15 degrees, which is the industry standard, the number would be lower):

Total satellites being used: 14 (GPS) + 6 (Galileo) + 6 (GLONASS) + 11 (BeiDou) + 4 (QZSS) + 5 (NavIC) = 46 satellites. Not all of these would have L5 bands; let’s assume 20 do.

So, the total number of channels required would be: 46*1 (L1) + 46*1 (L2) + 20*2 (L5) = 132 channels. In reality, this is still an exaggerated number. In the real world, no more than 100 channels are typically required. Claims of needing 400, 800, or even 1200 channels are overly futuristic and marketing/selling strategy. It will take more than 10–15 years to even approach the utilization of 300 channels.

Does All Satellites Used in DGNSS Provide the Same Level of Accuracy?

The accuracy of signals from GNSS satellites can vary due to several factors, including the satellite’s position, health, and atmospheric conditions affecting the signal’s travel to Earth. Differential GNSS (DGNSS) enhances overall accuracy by correcting these variable errors. However, the effectiveness of DGNSS corrections is influenced by the quality of the correction data, which depends on the proximity and condition of the reference station, as well as the quality of the communication link between the reference station and the DGNSS receiver. Therefore, it is crucial to closely examine the quality of the satellites being used for positioning.

About SurveyGyaan

SurveyGyaan is an educational initiative under the Surveyaan brand, which is a subsidiary of Nibrus Technologies Private Limited. Surveyaan specializes in drone manufacturing and the development of photogrammetry software. Surveypod specializes in DGNSS manufacturing with tilt gnss and non tilt gnss options.

Surveypod (Indian DGNSS(Dgps) Manufacturers): www.sur veypod.in

Surveyaan (Indian Drone Manufacturers): www.surveyaan.com

Surveyaan GeoWorkspace (Photogrammetry Software): app.surveyaan.com

DGNSS Series-Real Time Kinematic (RTK) and Post Processing Kinematic (PPK)

Tue, 10 Jun 2025 10:09:12 +0000

Global Navigation Satellite System (GNSS) technology has transformed how we navigate and collect location-based data. Real-Time Kinematic (RTK) and Post-Processing Kinematic (PPK) are two cutting-edge methodologies that have greatly improved the accuracy and dependability of GNSS data. In this blog article, we’ll look at the concepts, uses, and benefits of RTK and PPK GNSS technology.

RTK and PPK are techniques used to enhance the accuracy of GNSS measurements:

Real Time Kinematics

This form of measurement occurs when we have a GNSS base that communicates directly with the GNSS rover and delivers corrections via radio transmission. In this approach, both the base and the rover get signals from the same satellites and through this direct radio link the corrections are transmitted in real time, achieving a high accuracy in the same field of data capture.

Pros of Real Time Kinematics

Accuracy: RTK GNSS offers centimeter-level precision, making it ideal for applications requiring accurate location, such as surveying, construction, and agriculture.
Real-Time Corrections: RTK applies corrections to the GNSS signal in real time, allowing users to acquire precise location data in a fraction of seconds. This capability is especially useful for applications requiring fast input or change, such as machine control in construction.
Increased Efficiency: RTK technology allows for quicker data collecting and decision-making processes, which improves efficiency in a variety of applications. Surveyors, for example, may conduct fieldwork more rapidly with RTK, resulting in shorter project schedules.
Versatility: RTK GNSS may be used in a wide range of settings and situations, from metropolitan regions with tall structures to broad open fields. Its adaptability makes it appropriate.

Cons of Real Time Kinematics

Line-of-Sight Requirements: RTK GNSS requires a clear line of sight between the receiver and the satellites. Signal barriers, such as buildings, trees, or topography, might reduce performance and accuracy.
Reliance on Base Station: RTK systems rely on a nearby base station to send correction data to the rover receiver. This reliance restricts the range of operation and may be impractical in distant or inaccessible places without a network of base stations.
Vulnerability to Signal Interference: RTK GNSS signals are vulnerable to interference from sources such as electromagnetic interference (EMI), multipath reflections, and atmospheric conditions. Interference can impair signal reception and reduce accuracy, particularly in urban or industrial settings.
Infrastructure costs: Setting up and maintaining RTK infrastructure, including base stations and communication networks, may be expensive, especially for large-scale projects or businesses with several locations. Furthermore, continuous subscription costs for correction services may increase the overall cost of RTK GNSS use.

Post Processing Kinematics

PPK is an alternative to RTK that applies positional corrections retrospectively. This means that in PPK mode, the GNSS rover and GNSS base station do not need to be connected when functioning. You simply need to record raw GNSS data (logs), which are subsequently processed to produce accurate positioning data that may be utilized for computations in postprocessing.

Post-Processing Kinematic (PPK) GNSS technology offers unique advantages.

Pros of Post Processing Kinematics

High Accuracy: Similar to RTK, PPK GNSS provides centimeter-level accuracy, ensuring precise positioning data for various applications such as surveying, mapping, and asset management.
Flexibility in Data Collection: PPK technology allows users to collect GNSS data without the need for a real-time correction source or continuous communication with a base station. This flexibility is advantageous in remote or challenging environments where real-time corrections may not be available.
Cost savings: With PPK GNSS, there are no continuing subscription fees or infrastructure expenditures connected with real-time correction services. This can result in cost savings over time, particularly for firms that do regular or large-scale GNSS surveys.

Cons of Post Processing Kinematics

Delayed Results: Unlike RTK, which gives real-time positioning data, PPK GNSS requires gathered data to be post-processed in order to make corrections and obtain precise results. Depending on the processing procedure and software utilized, this could cause delays in receiving final positioning data.
Post-processing Complexity: To use PPK GNSS, users must acquire raw GNSS data in the field and process it using specific software or algorithms. This procedure can be difficult and may necessitate training or experience to provide correct findings.
Limited Real-Time Feedback: Without real-time corrections, users cannot discover and correct positional errors or anomalies during data gathering with PPK GNSS. Additional field checks or validation procedures may be required to verify data quality before results are finalized.

RTK and PPK GNSS technologies have transformed the landscape of precise positioning, enabling a wide range of industries to achieve unprecedented levels of accuracy in their location-based applications. As advancements in GNSS technology continue, the future holds even greater promise for enhanced accuracy and efficiency across diverse industries.

This brings us to the end of the blog. I hope this article gained some knowledge for you!

Please find the video on our YouTube channel from here.

Thank you for reading.

About SurveyGyaan

Surveypod (Indian DGNSS(Dgps) Manufacturers): www.sur veypod.in

Surveyaan (Indian Drone Manufacturers): www.surveyaan.com

Surveyaan GeoWorkspace (Photogrammetry Software): app.surveyaan.com

Errors in GNSS

Tue, 10 Jun 2025 06:56:56 +0000

Global Navigation Satellite Systems (GNSS) such as GPS, GLONASS, and Galileo are critical in providing accurate location information for a variety of applications ranging from navigation and surveying to agricultural and emergency services. However, the precision of GNSS positioning is susceptible to a variety of faults that can jeopardize the dependability of location data. In this blog article, we will look at various forms of GNSS errors and how they affect accuracy.

These are the factors that may make it difficult for a GNSS receiver to calculate an exact position and degrade precision.

Satellite Clock Errors

GNSS satellites are equipped with atomic clocks to provide precise timing signals.

However, variations in the satellite clocks can introduce errors in the ranging measurements, affecting the accuracy of position calculations. Different global systems use different types of atomic clocks, and most satellites will have multiple types of clocks on board. For e.g. Rubidium and Caesium are standard on GPS , Galileo has Hydrogen maser and Rubidium.

These clocks are incredibly accurate, but they aren’t perfect, and experience ‘drift’. This means they lose or gain one nanosecond for every three hours of time.

For example, 10 nanoseconds of clock error results in 3 meters of position error.

Orbit Errors

GNSS satellites travel in very precise, well-known orbits. However, like the satellite clock, the orbits do vary a small amount. Also, like the satellite clocks, a small variation in the orbit results in a significant error in the position calculated.

Orbital errors occur when the GNSS satellite is not exactly in the position that was predicted and transmitted through orbit data. Some GNSS surveying techniques require the final ephemerides to be used to guarantee the best solution for a position.

This error source can be reduced by means of relative measurement, or by post-processing when observed and post-processed orbit data of good quality are available.

Ionospheric Delay

The ionosphere is the layer of atmosphere between 50 and 1,000 km above the Earth. This layer contains electrically charged particles called ions due to solar radiation. These ions alter the transmission time of the satellite signals and can cause a significant amount of satellite position error (typically ±5 meters). Modelling the ionosphere is highly variable and more difficult to model. This is generally the largest error source in GNSS measurement, but it can be reduced by using relative or multi-frequency measurement.

Tropospheric Delay

The troposphere is the layer of atmosphere closest to the surface of the Earth. It is approximately 8 and 14 km deep, depending on the location on the Earth’s surface. Tropospheric errors are caused by temperature, density, pressure or humidity changes.. Here, the GNSS signal is mainly affected by water vapour, which varies is a lot in time and space.

Multipath

Multipath error occurs when a signal from the same satellite reaches a GNSS antenna via two or more paths, such as reflected off the wall of a building. The reflected signal clearly has to travel further to reach the antenna and so it arrives with a slight delay. In an environment with tall houses or trees, multipath errors are more common. This error source can be partially reduced by observing over a longer period and with good quality GNSS equipment. Also, to reduce multipath errors place the GNSS antenna in a location that is away from the reflective surface.

Receiver Noise

Receiver noise refers to the position error caused by the GNSS receiver hardware and software. All GNSS receivers are subject to other radio waves that occur naturally or through other processes. These other radio waves, along with other types of electrical interference are what is known as background noise, and impact the ability of the receiver to ‘hear’ the GNSS signals. High-end GNSS receivers tend to have less receiver noise than lower-cost GNSS receivers. Calibration and signal processing techniques are employed to minimize these errors, but they can still impact accuracy.

Impact on Accuracy

Positional Inaccuracy: Cumulative effects of the mentioned errors can lead to significant inaccuracies in the calculated position. This is particularly critical in applications where precise positioning is essential, such as in aviation, surveying, and autonomous vehicles.
Time-to-First-Fix: Errors can also impact the time it takes for a GNSS receiver to acquire the first fix. In scenarios where rapid and accurate positioning is crucial, delays in acquiring a fix can have serious consequences.
Navigational Integrity: In safety-critical applications, like aviation, GNSS errors can compromise the navigational integrity of the system. This is why redundancy and augmentation systems are often used to enhance accuracy and reliability.
Increased Uncertainty: Users relying on GNSS for navigation or surveying may experience increased uncertainty in their results. This uncertainty can be a limiting factor in applications where precision is paramount.

While GNSS has revolutionized navigation and positioning, understanding and mitigating errors are crucial for ensuring accuracy. Users should be aware of the various error sources and employ techniques such as differential corrections, augmentation systems and the use of multiple constellations to enhance GNSS performance

This brings us to the end of the blog. I hope this article gained some knowledge for you!

Please find the video on our YouTube channel from here.

Thank ou for reading.

About SurveyGyaan

Surveypod (Indian DGNSS(Dgps) Manufacturers): www.sur veypod.in

Surveyaan (Indian Drone Manufacturers): www.surveyaan.com

Surveyaan GeoWorkspace (Photogrammetry Software): app.surveyaan.com

DGNSS Series- Introduction

Fri, 06 Jun 2025 09:54:42 +0000

In the ever-evolving landscape of technology, precision is paramount, especially when it comes to location-based services. This blog series delves into the world of Differential Global Navigation Satellite Systems (DGNSS). In this inaugural post, we will unravel the diverse domains where accuracy is not just a preference but an absolute necessity and also take you on a journey into the cosmos of GNSS.

Applications

Surveying and Mapping

In the world of surveying and mapping, accuracy is indispensable for creating reliable and detailed spatial representations.
Accurate land surveying is essential for a variety of purposes, such as determining property boundaries, creating topographic maps, and supporting the construction of buildings and infrastructure.

Navigation

It helps in ensuring safe navigation, particularly in congested or hazardous locations.
Display real-world scenarios in which precise location is a nautical requirement.

Precision Agriculture

Transforming agriculture by providing precise planting, fertilization, and harvesting.
Illustrate the impact of accuracy on resource optimization, cost reduction, and increased crop yields.

Aviation

Accurate navigation is essential for safe takeoffs, landings, and en route operations in aviation.
Highlight instances where even minor deviations can pose serious risks, underlining the importance of accuracy.

Emergency Response and Public Safety

Examine the vital role of accurate location data in emergency situations, such as natural disasters or accidents.
Showcase how accurate location data can significantly improve response times and aid in effective crisis management.

Since now we know why accuracy is a very important factor in our daily commutes, let us take a journey into the world of GNSS.

What is GNSS?

A standalone GNSS (Global Navigation Satellite System) is a constellation of satellites that relies exclusively on satellite signals to calculate the user’s position, velocity, and time. It provides signals from space that transmit positioning and timing data to GNSS receivers. The receivers then use this data to determine location.

The most well-known GNSS is the Global Positioning System (GPS), although there are also GLONASS (Russia), Galileo (European Union), and BeiDou (China) satellite navigation systems.

While Global Navigation Satellite Systems (GNSS), such as GPS, provide widespread and reliable positioning information, the limitation of the standalone GNSS is in its accuracy.

Standalone GNSS such as GPS will have an error of 4–5cm with respect to the real-world coordinates. To address this limitation, Differential GNSS (DGNSS) is employed. This can bring the error up to the cm or mm level.

This brings us to the end of the blog. I hope this article gained some knowledge for you!

Please find the video on our YouTube channel from here.

Thank you for reading.

About SurveyGyaan

Surveyaan: www.surveyaan.com

Surveyaan GeoWorkspace: app.surveyaan.com