Short Answer:
Relative positioning and absolute positioning are two methods used in surveying to determine the location of a point. Relative positioning finds a point’s position based on its distance or angle from another known point. It is useful for local surveys and small projects. Absolute positioning, on the other hand, gives the exact location of a point using a fixed global coordinate system, such as GPS.
The main difference is that relative positioning is based on comparison with nearby points, while absolute positioning gives coordinates that are fixed and universal. Both are important in civil engineering depending on the type of work and required accuracy.
Detailed Explanation:
Difference between relative and absolute positioning
In surveying and geospatial work, understanding the position of points on the earth’s surface is essential for accurate planning and construction. Two main methods are used for this: relative positioning and absolute positioning. While both help in locating points, they work in different ways and serve different purposes based on the project needs.
Relative positioning
Relative positioning is a method in which the location of a point is determined by measuring its distance, angle, or height difference from another nearby known point. It does not rely on a global reference system. Instead, it focuses on local accuracy, which means how accurately one point is located in relation to another.
This method is commonly used in:
- Construction site layout
- Property boundary marking
- Road alignment and bridge layout
- Small area mapping
Tools like total stations, theodolites, and traditional leveling instruments are used for relative positioning. In GPS-based surveying, relative positioning is also done by comparing signals from satellites to two or more GPS receivers—this is called differential GPS or RTK (Real-Time Kinematic) method.
The advantage of relative positioning is that it provides high precision in short-range surveys, even when absolute coordinates are not known.
Absolute positioning
Absolute positioning is a method where the position of a point is found directly using a global coordinate system, such as latitude, longitude, and elevation. It uses signals from satellites, like the Global Positioning System (GPS), to find the location on Earth with respect to a fixed reference like the center of the Earth or sea level.
It is commonly used in:
- Mapping large areas
- Navigation systems
- GIS (Geographic Information Systems)
- Remote location surveys
Absolute positioning gives a unique location to any point on the globe. It is especially useful when connecting the survey with satellite maps, integrating data into GIS software, or sharing location information across different regions.
Modern devices like handheld GPS units or drone-based survey systems use absolute positioning.
Key difference
The key difference is that relative positioning shows how far and in which direction a point is from another point, while absolute positioning tells exactly where a point is on Earth. Relative positioning is better for small-scale and high-accuracy work. Absolute positioning is better for large-scale, map-based work and when data must match global coordinates.
In many cases, both methods are used together. For example, a project may start with absolute GPS coordinates, and then detailed layout work is done using relative methods for high precision.
Conclusion:
Relative and absolute positioning are two different ways to determine point locations in surveying. Relative positioning is based on measuring between known nearby points and is useful for local accuracy. Absolute positioning uses global coordinates like GPS to find fixed locations on Earth. Both methods are important and are used depending on the type of survey and level of precision needed.