Taking levels

Summary

In this instructional video, the presenter demonstrates the process of establishing ground levels on a construction site. Beginning with the importance of a known reference point, or job datum, the video outlines the necessary steps to record various height measurements using a level book. It details the significance of accurate readings, the different types of sights (backsight, intermediate sight, foresight), and the procedure for moving equipment while ensuring precision. The presenter also emphasizes the importance of meticulous record-keeping to avoid the need for re-surveying, setting the stage for subsequent calculations.

Takeaways

• 📏 Establishing a job datum is crucial for determining ground levels around a construction site.
• 🔍 The job datum is marked by a fixed point (like a nail or curb) that serves as a reference for height measurements.
• 📝 The height of the datum can be a nominal value (e.g., 10 meters) or a specific height above sea level, requiring input from a registered surveyor.
• 🌍 Registered surveyors use the Spatial Information System to find survey marks and determine heights above sea level.
• 📖 A Rise and Fall level book is essential for recording readings during the leveling process.
• 🔢 The first reading taken is called a backsight, which establishes the baseline for further measurements.
• 🏗️ Intermediate sights are taken between backsights and foresights to gather data from various points around the site.
• ⚙️ Accurate readings and meticulous record-keeping are vital to avoid having to redo surveys due to errors.
• 🔄 After a series of readings, the leveling instrument may be repositioned, while the staff remains stationary to take further measurements.
• 📊 Future calculations will analyze the recorded data to determine differences in height between measurement points.

Q & A

What is a job datum in surveying?

A job datum is a reference point on a job site that has a known height, which is used as a baseline for measuring other levels around the site.

Why is it important to establish a job datum?

Establishing a job datum is crucial for ensuring accurate height measurements across the construction site, providing a consistent reference point for all leveling activities.

What might a job datum physically be?

A job datum can be a physical mark, such as a nail, a mark on a curb, or any other stable point that is unlikely to be moved.

What is the typical height assigned to a job datum, and why?

Typically, a job datum is assigned a nominal height, such as 10 meters, to avoid using negative numbers in readings, simplifying the measurement process.

What role does a registered surveyor play in establishing a job datum?

A registered surveyor locates a survey mark or Australian Height Datum, uses the Spatial Information System to find its coordinates and height above sea level, and transfers that information to the job datum.

How is data recorded during the leveling process?

Data is recorded in a level book, specifically in a format called the Rise and Fall level book, where readings are logged under backsight, intermediate, and foresight columns.

What are the main types of readings taken during the surveying process?

The main types of readings are backsight (from a known point), intermediate sights (between points), and foresight (to a new point).

What is the significance of accuracy in the surveying process?

Accuracy in recording readings is vital because errors can lead to incorrect calculations, necessitating a return to the job site for re-surveying, which can be time-consuming and costly.

What happens after all the readings are taken?

After all readings are taken, they are recorded, and the next steps involve calculating the differences between the recorded levels, which will be covered in a subsequent video.

What is a foresight reading and when is it taken?

A foresight reading is taken when looking forward to the next point in the leveling process. It represents the last reading from a position before moving to a new one.