Short Answer:

GPS works in surveying by using signals from satellites to calculate the exact position of a point on the Earth. A GPS receiver on the ground collects signals from at least four satellites and calculates the distance to each one. With this data, it finds the location in terms of latitude, longitude, and elevation.

Surveyors use this method to mark points, measure distances, and map areas with high accuracy. GPS helps in fast data collection without needing direct line-of-sight between stations, making it suitable for large and difficult terrains.

Detailed Explanation:

How GPS works in surveying

GPS, or Global Positioning System, is a satellite-based technology that helps determine the precise location of any point on Earth. In surveying, GPS is used to measure coordinates (X, Y, Z) of land or features with high accuracy. This system is very useful for land development, road construction, and mapping projects.

Components involved in GPS surveying:

1. GPS Satellites (Space Segment):
   A group of 24 or more satellites orbit the Earth and send continuous radio signals containing the time and their location.
2. GPS Receiver (User Segment):
   A device used by the surveyor on the ground that picks up signals from satellites to calculate position.
3. Control Segment:
   Ground stations that monitor and maintain satellite health and data accuracy.

Working steps of GPS in surveying

1. Signal reception

The GPS receiver collects signals from at least four satellites at a time. Each signal contains the time it was sent and the satellite’s position in space. Since the signals travel at the speed of light, the time taken to reach the receiver helps in calculating the distance to the satellite.

2. Distance calculation

The distance between each satellite and the receiver is calculated using the travel time of the signal. This distance is called the pseudorange.

3. Trilateration

Once the receiver knows the distance from at least four satellites, it uses trilateration to calculate its own position in 3D space (latitude, longitude, and elevation).

• With 1 satellite: Location is somewhere on a sphere.
• With 2 satellites: Location is on the circle where two spheres intersect.
• With 3 satellites: Location is one of the two points where all three spheres intersect.
• With 4 satellites: The exact point on the Earth’s surface is determined, including elevation.

4. Coordinate output

The receiver then converts the position into surveying coordinates like UTM (Universal Transverse Mercator) or local grid coordinates. These coordinates are displayed and stored for further processing.

Modes of GPS surveying

• Static Surveying: The receiver stays fixed for a long time to get very precise measurements.
• Kinematic Surveying: Used for moving surveys like roads and railways.
• Real-Time Kinematic (RTK): Provides real-time coordinates using a base station and a mobile unit (rover).
• Differential GPS (DGPS): Uses corrections from a known base station to improve the accuracy of the mobile receiver.

Benefits in surveying

• No need for direct line-of-sight between points.
• Works over long distances and in tough terrains.
• Reduces manual errors and saves time.
• Provides digital data directly usable in software.
• Enables quick mapping and layout work for construction.

Conclusion

GPS works in surveying by calculating the position of a ground point using satellite signals and time measurements. This method is accurate, fast, and suitable for modern surveying needs in all types of environments. It replaces traditional tools and improves both productivity and precision.