Geodesy is the scientific study of the Earth’s shape, size, and gravity field. Surveying, on the other hand, is the process of measuring and determining the positions of points and features on the Earth’s surface.
In the context of global navigation satellite systems (GNSS), geodesy and surveying work together to accurately determine the position and orientation of a location. This is done by using a combination of satellite signals, ground-based measurement equipment, and advanced mathematical models.
Geodesy provides the foundation for GNSS positioning by establishing a reference frame for the Earth. This includes determining the shape and size of the Earth, as well as the variations in its gravity field. Surveying, on the other hand, uses this reference frame to determine the positions of points and features on the Earth’s surface.
GNSS systems, such as GPS, GLONASS, and Galileo, use a network of satellites in orbit around the Earth to transmit signals to a receiver on the ground. The receiver uses these signals to determine its location and orientation relative to the satellites.
Geodetic surveying is the process of determining the position of a point relative to a reference frame. This is done by measuring the angles and distances between the point and a set of reference points. The reference points are typically located on known points, such as landmarks, buildings, or survey markers.
In addition to determining the position of a point, geodetic surveying can also be used to measure changes in the Earth’s surface, such as subsidence, uplift, or deformation. This is done by repeatedly measuring the positions of points over time and comparing the results to detect any changes.
Geodetic surveying is an essential tool for GNSS positioning and navigation. It provides the foundation for accurately determining the position and orientation of a location, which is critical for a wide range of applications, such as transportation, construction, land management, and emergency response.
Meaning and Application
Geodesy and Surveying are related fields that deal with the measurement and study of the earth’s shape, size, and gravity field. Global Navigation Satellite Systems (GNSS) are used in these fields to accurately determine the location and orientation of objects on the earth’s surface.
The application of GNSS in Geodesy involves using satellite-based measurements to determine the precise location of points on the earth’s surface, as well as the shape and size of the earth itself. This information is used to create accurate maps, charts, and other geodetic data that are used for a wide range of applications, including land management, navigation, and resource exploration.
In Surveying, GNSS is used to determine the location of points on the earth’s surface for a wide range of applications, including construction, land management, and resource exploration. Surveyors use GNSS receivers to determine the location and orientation of objects on the earth’s surface, and this information is used to create accurate maps and charts of the earth’s surface.
Overall, GNSS plays a critical role in both Geodesy and Surveying, providing accurate and reliable location and orientation information that is essential for a wide range of applications.
Geoid, Spheroid, and Ellipsoid of Revolution
In geodesy and surveying, the geoid, spheroid, and ellipsoid of revolution are all used to model the shape of the Earth for the purpose of mapping and navigation.
The geoid is a mathematical model of the Earth’s surface that represents the shape of the Earth as it would be if it were covered by a sea of constant density. It is determined by measuring the deviation of the Earth’s gravity field from the theoretical field of a perfect ellipsoid.
The spheroid, also known as an oblate spheroid, is an elliptical shape that approximates the shape of the Earth. It is a simplified model of the Earth that is used in navigation and mapping, and is the basis for many map projections.
The ellipsoid of revolution is an ellipsoid shape that is created by rotating an ellipse around its minor axis. It is used in satellite navigation systems such as GPS and is the reference surface for many map projections. The shape of the ellipsoid is determined by the shape of the Earth and is adjusted to fit the geoid as closely as possible.
Overall, these three models are used to represent the shape of the Earth in different ways and are crucial in the field of geodesy and surveying to improve the accuracy of mapping and navigation using global navigation satellite systems.
Use of Gravity in Geodesy, Coordinate System
Geodesy, the study of the Earth’s shape, gravity field, and rotation, makes use of gravity in several ways. One of the main ways is through the use of gravimetry, which measures variations in the Earth’s gravity field. These variations can be used to study the Earth’s crust, mantle, and core, as well as to detect changes in the Earth’s rotation and mass distribution.
Another way in which gravity is used in geodesy is through the use of a coordinate system. Geodesy uses a variety of coordinate systems, including the global positioning system (GPS), which uses a 3D cartesian coordinate system. This system allows for precise measurements of location and movement, and is used in a variety of applications, including surveying and navigation.
In surveying, gravity is used to determine the elevation of a point, as well as to correct for variations in the Earth’s gravity field. This is particularly important in areas where the Earth’s gravity field is not uniform, such as near mountains or in areas with large amounts of water.
In global navigation satellite systems, gravity is also used to determine the location of a point. These systems rely on a network of satellites in orbit around the Earth, and use the principles
of gravity to calculate the position of a point on the Earth’s surface. These systems are used in a wide range of applications, including navigation, mapping, and surveying.
Geodetic Reference Systems
Geodetic reference systems in geodesy and surveying refer to the frameworks used to define the position and orientation of points on the Earth’s surface. These systems are used to accurately measure and map the Earth’s surface and are crucial in the field of global navigation satellite systems (GNSS).
There are several different types of geodetic reference systems, including:
1. Geodetic Datums:
These are the foundation of any geodetic reference system, and they define the origin and orientation of the system. The most commonly used datum in surveying and mapping is the World Geodetic System (WGS 84), which is the standard used by GNSS systems.
2. Projected Coordinate Systems:
These systems are used to map large areas of the Earth’s surface, such as countries or regions. They are based on a projection of the Earth’s surface onto a flat plane, which allows for easy measurement and mapping of large areas.
3. Geographic Coordinate Systems:
These systems are based on latitude and longitude coordinates and are used for navigation and location-based services. The most widely used geographic coordinate system is the WGS 84.
4. Vertical Reference Systems:
These systems are used to measure and map the elevations of points on the Earth’s surface. They are often used in conjunction with other reference systems to provide a complete picture of the Earth’s surface.
Overall, geodetic reference systems play an important role in the field of GNSS and surveying. They provide the framework for accurate mapping and measurement of the Earth’s surface, which is essential for navigation and other location-based services.
GNSS stands for Global Navigation Satellite System. It is a system that uses a network of satellites in orbit around the Earth to provide location and time information to users on the ground, in the air, or at sea. The most widely used GNSS is the Global Positioning System (GPS), which is operated by the United States government. Other GNSS include the Russian GLONASS, the European Galileo, and the Chinese BeiDou. These systems work by transmitting signals from the satellites to a receiver on the ground, which then uses the information to calculate the user’s location and time. GNSS is used in a wide range of applications, including navigation, surveying, mapping, and timing.
GPS Coordinate System
The GPS coordinate system in the global navigation satellite system (GNSS) uses a three-dimensional cartesian coordinate system to specify the position of a point on the Earth’s surface. The system uses a reference ellipsoid (or geoid) to approximate the shape of the Earth and define the origin of the coordinate system. The coordinates are measured in terms of latitude, longitude, and altitude (or elevation) relative to the reference ellipsoid. The latitude and longitude values are given in degrees and represent the angular distance from the equator and the prime meridian, respectively. The altitude value is given in meters or feet and represents the distance above or below the reference ellipsoid. Together, these three coordinates define a unique point on the Earth’s surface and can be used for navigation, mapping, and other purposes.
Local Coordinate system
A local coordinate system in a global navigation satellite system (GNSS) is a system of coordinates used to define the position of a point within a specific geographic area. This system is based on a reference point, such as a specific location on the Earth’s surface, and uses a set of coordinates (such as latitude, longitude, and altitude) to define the position of other points within that area. These coordinates are often used in navigation and mapping applications, as they allow for more precise and accurate positioning than a global coordinate system, such as the WGS 84 system. Additionally, local coordinate systems can be used to account for variations in the Earth’s shape and rotation, which can affect the accuracy of GNSS signals in certain areas.
- Increased Accuracy: With advancements in technology, GNSS systems have become more accurate and reliable in determining a user’s location. This has led to greater precision in navigation, surveying, and mapping applications.
- Multi-Constellation Support: With the launch of new satellite constellations such as Galileo and BeiDou, GNSS systems are now able to access multiple satellite systems, providing increased coverage and redundancy.
- Integration with Other Systems: GNSS systems are now being integrated with other technologies such as cellular networks and wireless sensor networks, providing new capabilities such as real-time location tracking and remote monitoring.
- Development of Augmentation Systems: The implementation of augmentation systems such as the Wide Area Augmentation System (WAAS) and the European Geostationary Navigation Overlay Service (EGNOS) have improved the accuracy and reliability of GNSS systems in areas where signals may be weak or obstructed.
- Advancements in Receiver Technology: With the development of software-defined GNSS receivers, users are now able to customize their GNSS systems to suit their specific needs. This has led to the creation of new applications such as unmanned aerial vehicles and autonomous vehicles.
- Increased Security Measures: With the increased reliance on GNSS systems in critical infrastructure, security measures have been put in place to protect against jamming, spoofing, and other malicious attacks on the system.
Step Wise Transformation
- The first step in the transformation of the global navigation satellite system (GNSS) was the development of the first generation of GNSS systems, such as the US Global Positioning System (GPS) and the Russian GLONASS. These systems were primarily used
for military and government purposes, and were not widely available to the general public.
- The second step was the introduction of the second generation of GNSS systems, such as the European Galileo and the Chinese BeiDou. These systems offered improved accuracy and reliability, and were made available for civilian use.
- The third step was the development of the third generation of GNSS systems, such as the Indian Regional Navigation Satellite System (IRNSS) and the Japanese Quasi-Zenith Satellite System (QZSS). These systems offered even higher accuracy and reliability, and were designed to be used for a variety of applications, including transportation, agriculture, and disaster management.
- The fourth step is the integration of multi-constellation and multi-frequency systems to provide even more precise and reliable navigation. This will be achieved through the use of new technologies such as precise point positioning, which uses multiple GNSS signals from multiple constellations to provide extremely accurate location data.
- The fifth step is the integration of GNSS with other technologies such as internet of things (IoT) and artificial intelligence (AI) to provide new, innovative applications and services such as smart cities, autonomous vehicles and precise agriculture.
- The final step is the continued development and improvement of GNSS technology to ensure it remains at the forefront of global navigation and positioning, and continues to provide a wide range of benefits to users around the world.
Seven Parameter Transformation
In a Global Navigation Satellite System (GNSS), the position of a receiver on the Earth’s surface can be determined by measuring the time delay of signals from multiple satellites. However, the measured time delays are affected by various errors, such as clock errors, ionospheric and tropospheric delays, and multipath. In order to achieve high accuracy in positioning, these errors must be corrected.
One method used to correct errors in GNSS measurements is the use of a seven-parameter transformation. The seven parameters are: three for translation (to account for differences in the coordinate systems of the satellites and the receiver), three for rotation (to account for differences in the orientations of the coordinate systems), and one for scale (to account for differences in the units of measurement).
The translation parameters are used to account for the differences in the positions of the reference point (also called the origin) of the coordinate systems used by the satellites and the receiver. The rotation parameters are used to account for the differences in the orientations of the coordinate systems, while the scale parameter is used to account for differences in the units of measurement.
By applying these seven parameters to the measured time delays, it is possible to transform the satellite coordinates to the receiver coordinates, and thus to accurately determine the position of the receiver on the Earth’s surface.
The process to get the 7-parameter transformation is called Helmert Transform, including translation, rotation and scaling are applied in a specific order which is called affine transformation. The process of obtain those parameters need to have a reliable reference point with known coordinate on both systems, either on satellite and receiver system.
- Code-based measurements: This technique involves measuring the time delay between the transmission of a signal from a satellite and its reception by a receiver. The difference in time is then used to calculate the distance between the satellite and the receiver.
- Phase-based measurements: This technique involves measuring the phase difference between the signal transmitted by a satellite and the signal received by a receiver. The phase difference is then used to calculate the distance between the satellite and the receiver.
- Carrier-phase measurements: This technique involves measuring the phase of the carrier wave of the signal transmitted by a satellite. The phase difference is then used to calculate the distance between the satellite and the receiver.
- Dual-frequency measurements: This technique involves using two different frequencies to calculate the distance between the satellite and the receiver. The difference in the phase of the two frequencies is used to calculate the distance.
- Multi-path measurements: This technique involves measuring the signal that is reflected by objects on the ground before it reaches the receiver. The time delay between the direct signal and the reflected signal is used to calculate the distance between the satellite and the receiver.
- Angle of arrival measurements: This technique involves measuring the angle of arrival of the signal at the receiver. The angle is then used to calculate the position of the satellite relative to the receiver.
In geodesy and surveying, a static survey is a type of survey in which observations are made over a period of time, typically several minutes to several hours, to determine the precise location of a point on the Earth’s surface. The primary goal of a static survey is to determine the coordinates (such as latitude, longitude, and elevation) of a point on the Earth’s surface with a high degree of accuracy.
Global Navigation Satellite Systems (GNSS) such as GPS, GLONASS, Galileo, and Beidou, are used in static surveys to determine the precise location of a point on the Earth’s surface. The GNSS receiver records the signals from multiple satellites, and uses the relative time of arrival of the signals to calculate the exact location of the receiver. The more satellites that are used in the calculation, the more accurate the location will be.
Static GNSS surveying requires a receiver that is capable of recording the raw data (i.e. the pseudoranges and carrier phases) from the GNSS satellites. The raw data is then post-processed using specialized software to calculate the precise location of the receiver. The software uses a mathematical model to calculate the position of the receiver, taking into account the geometry of the satellite constellation, atmospheric delays, and other errors.
When the observation time is longer and atmospheric effects are significant, the software uses the known positions of the GNSS stations to form a network and correct the atmospheric effects and estimate the position, this is called “network RTK” which stands for Real Time Kinematic.
It is important to note that GNSS surveying also often involves other surveying methods as well, for example for measuring height difference, such as leveling.
Rapid Static Survey
A rapid static survey in geodesy and surveying refers to a method of obtaining precise positioning measurements using a global navigation satellite system (GNSS) receiver. The survey is performed in a static mode, meaning that the receiver is stationary and records observations over a period of time. The observations are then processed to determine the precise position of the receiver.
The survey typically lasts between 30 minutes to 1 hour, with the receiver recording observations from multiple satellites at different intervals. The receiver records the pseudorange (the distance from the satellite to the receiver) and the carrier phase (the phase of the signal from the satellite) for each satellite. These observations are then used to calculate the precise position of the receiver using a process called differential positioning.
Rapid static surveys are commonly used in applications such as construction, mapping, and land surveying. The accuracy of the survey is dependent on the number of satellites in view, the signal-to-noise ratio, and the duration of the survey. However, a rapid static survey can achieve sub-centimeter accuracy, making it an ideal method for precise positioning applications.
Overall, the use of GNSS technology in rapid static surveys has greatly improved the accuracy and efficiency of geodetic and surveying work in many areas. It allows for the fast acquisition of precise positioning measurements, which is essential in many applications, including construction, mapping, and land surveying.
Kinematic survey is a method of surveying that involves measuring the movement of a point or object over time. In geodesy and surveying, kinematic surveys are commonly used to track the movement of points on the Earth’s surface, such as the movement of tectonic plates or the deformation of buildings and structures.
Global Navigation Satellite Systems (GNSS) are a type of satellite-based positioning system that allows users to determine their location, speed, and time using signals from a network of satellites. In kinematic surveying, GNSS receivers are used to continuously track the movement of a point or object over time by measuring the position of the receiver at regular intervals.
One of the main advantages of kinematic surveying using GNSS is that it allows for high-accuracy measurements over large distances and in real-time. This makes it useful for a wide range of applications, such as monitoring the movement of tectonic plates, tracking the deformation of buildings and structures, and measuring the movement of vehicles and other mobile assets.
Overall, kinematic surveying using GNSS is a powerful tool for measuring and understanding the movement of points and objects on the Earth’s surface. It has many potential applications and can be used in a wide range of fields, including geodesy, surveying, and civil engineering.
RTK (Real-Time Kinematic) surveying is a method used in geodesy and surveying that utilizes real-time data from global navigation satellite systems (GNSS) such as GPS and GLONASS to determine the precise location and movement of a survey point.
This method utilizes a base station, which is placed at a known location and constantly receives satellite signals, and a rover, which is placed at the survey point and receives signals from the base station and satellites. The base station and rover communicate with each other to determine the precise location and movement of the survey point.
RTK surveying is commonly used for land surveying, engineering, construction, and mapping applications. It allows for highly accurate and precise measurements, with an error margin of just a few centimeters. It also provides real-time data, allowing for quicker and more efficient surveying.
Overall, RTK surveying is a powerful tool that utilizes advanced technology to provide precise and accurate measurements, making it a valuable tool in various fields including geodesy and surveying.
Pre survey Preparations
- Equipment preparation: Before starting the survey, it is important to ensure that all equipment is in good working condition and properly calibrated. This includes GNSS receivers, antennas, total stations, and other necessary tools.
- Data collection plan: Develop a plan for collecting data that includes the specific points that need to be surveyed, the order in which they will be surveyed, and the method of data collection.
- Site preparation: Survey locations should be cleared of any debris or obstructions that may interfere with data collection. It is also important to ensure that the survey area is safe and free from any hazards.
- Base station setup: Establish a base station at a known location to serve as a reference point for the survey. This base station should be equipped with a GNSS receiver and antenna, and should be set up in an open area with good visibility to the sky.
- Coordinate system selection: Select the appropriate coordinate system for the survey and ensure that all equipment is set up to use this system.
- Data backup and storage: Prepare a backup plan for data storage and ensure that all data is properly backed up and stored in case of equipment failure or other issues.
- Communication plan: Develop a plan for communication between survey team members to ensure that everyone is aware of the survey progress and any issues that may arise. This can include using radios or other forms of communication.
- Test run: Conduct a test run of the survey to ensure that all equipment is functioning properly and that the data collection plan is feasible. This can help identify and resolve any issues before the survey begins.
Total Station is a surveying instrument that combines electronic distance measurement (EDM) technology with an angular measurement system (such as a theodolite) to provide accurate measurements for surveying and construction projects. It can be used for a variety of tasks, including measuring distance, angles, and elevations, and determining coordinates of points.
In geodesy and surveying, Total Station can be used to establish control points and survey boundary lines, as well as to create detailed topographic maps and digital terrain models. It can also be used in construction projects to ensure that building foundations and structures are level and properly aligned.
On the other hand, Global Navigation Satellite System (GNSS) is a system of satellites that transmit signals that can be used to determine the location and time of a receiver on Earth. The most well-known GNSS is the Global Positioning System (GPS), which is operated by the U.S. Department of Defense. Other GNSS include the Russian GLONASS and the European Union’s Galileo.
Both Total Station and GNSS can be used together to provide more accurate and precise measurements in surveying and geodesy. GNSS can provide a quick and easy way to establish control points, while Total Station can provide more precise measurements for detailed survey work. The combination of both can provide the best solution for surveying, mapping and positioning.