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Topographical Survey Explained

28/04/2021

Studio Victoria

3 minutes

To carry on from our last article on Topographic Surveys with Drones, in this article, we'll dive deeper by answering the following questions: What is a Topographical Survey? How are Topographical Surveys useful? What are the methods of conducting a Topographical Survey? What is the difference between Real-Time Kinematic and Post-Processing Kinematic? and What outputs can you expect from a topographic survey? Keep reading to learn about how you can #ONEUPYOURBUSINESS!

WHAT IS A TOPOGRAPHICAL SURVEY?

In the simplest term, a topographical survey is just a collection of coordinates and height measurements for a designated area that will produce different outputs: elevation profiles, contour maps, terrain models, etc. The area's features, such as human-made structures, vegetation, etc., aren't strictly considered topographic information.

HOW ARE TOPOGRAPHICAL SURVEYS USEFUL?

Topographical surveys provide several sectors with invaluable information to develop and deliver their projects. Elevation profiles and contour maps aid in the decision-making process of earthworks, excavations, preventing potential flood areas, terrain restructuring (flattening, for example).

HOW CAN YOU CONDUCT A TOPOGRAPHICAL SURVEY?

Traditionally, when conducting a topographical survey, to make sure that the outputs have the correct scale, first and foremost, you'd mark the area's boundaries and place Ground Control Points (also known as GCPs) and get their coordinates with a handheld GPS device. Ideally, you'd only use calibrated GCPs and handheld GPS devices to ensure accuracy and precision. After this, you'd lay the grid lines across the area and go through the painstaking process of moving the total station around to acquire the dataset and move on to processing it into the elevation profiles and contour maps.

Fortunately, technology has come to the rescue, and tools like drones and Software suites have dramatically improved the survey workflow. You no longer need to spend countless hours walking around the area, carrying the total station, and paying attention to the terrain to avoid tripping over and injuring yourself. Just hire a drone operator, get them to come to your land, and the drone will do all the hard work in a matter of hours.

By using drones on your upcoming survey, you can get numerous advantages over the traditional methods:

  • Reduced time and increased efficiency: Compared to the traditional method, drones can cover up to 400 hectares per hour, delivering results much quicker. In one single flight, a drone topographic survey can deliver elevation profiles, 3D map, digital bare terrain model, and digital surface model
  • Less costly: with most drone surveys taking only a day, you'll save a considerable amount of money by not having the surveyor for weeks on end on your land
  • Increased safety: more often than not, the surveyed terrain can be in less than ideal conditions, posing potential risks to the surveyor. Drones eliminate this risk by flying around the land, letting the operator stay in a safe place
  • Precision and accuracy: With reports showcasing that surveys often use 1.5 centimetres per pixel and in some instances 3 centimetres per pixels, drones can offer better precision and accuracy with 0.6 centimetres per pixel with multi-rotor drones and 0.7 centimetres per pixel with fixed-wing drones. In cases where precision and accuracy are critical, drones can also offer the best resolution of 1 millimetre per pixel

WHAT IS THE DIFFERENCE BETWEEN GROUND CONTROL POINTS, REAL-TIME KINEMATIC, AND POST-PROCESSED KINEMATIC?

As we explained earlier, to ensure that the topographic map is to scale, you'd use calibrated GCPs and handheld GPS devices. This traditional method is still relevant today with drone technology, as you can import the GPCs into the outputs.

As useful as GCPs are, the best survey-grade drones often come equipped with positioning-correction technologies: Real-Time Kinematic (RTK) and Post-Processed Kinematic (PPK) to receive much better accurate and precise measurements. The main differences between RTK and PPK are:

  • Real-Time Kinematic: This is where the drone's positioning is corrected in real-time when the drone is in flight. It usually uses a single ground station, where both the drone and the ground station are in permanent communication with a data link enabling the drone to correct its positioning. Think of RTK as similar to the "lane assist" of your car
  • Post-Processed Kinematic: Unlike the RTK, PPK corrects the positioning accuracy after the flight by storing the coordinates in a memory card or disk. As this method doesn't need a data link and is particularly useful in unideal weather situations or places where the communication between the ground station and the drone could be affected

WHAT OUTPUTS CAN YOU EXPECT FROM A TOPOGRAPHIC SURVEY?

The most common outputs of a traditional topographic survey are the elevation profiles, contour maps, and terrain models, all in a CAD-compatible format. If you have used a drone, you can also expect 3D models, orthomosaics, digital terrain models, and digital surface models.

Bear in mind that most drone operators or surveyors won't go to the extent of making the outputs fully BIM-compatible.

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