Avvir Academy
April 21, 2023

Why Surveying Control Points Are Essential for Your Jobsite

You've likely found yourself debating the necessity of surveying control points when deploying laser scanners on your jobsite. After all, we're always looking for ways to streamline processes and boost efficiency, right? Well, when it comes to surveying control points, there's no one-size-fits-all answer. In some situations, they're indispensable for capturing accurate data, while in others, they might not be as crucial. But how do you know when to leverage them? 

In this article, we'll dive into the specifics of control points, exploring their role in construction sites and helping you determine when to leverage them and when you can confidently skip them without compromising the integrity of your project. Let's first refresh our understanding of surveying control points and their significance on the jobsite.

What Are Surveying Control Points?

Surveying control points: engineer using handheld GPS land area surveying equipment

Control points are reference points with known coordinates, used to create a consistent coordinate system for construction projects. These points are essential for land surveyors to accurately position elements on a jobsite, based on digital plans or Building Information Modeling (BIM) models.

For instance, ground control points (GCPs) are a type of control point used in photogrammetry, Geographic Information System (GIS), and Global Navigation Satellite Systems (GNSS) applications, ensuring accurate geospatial data. Other types of control points include geodetic control points, local control points, and survey monuments, all of which serve different purposes depending on the project requirements.

A control network is a set of interconnected surveying control points that provide horizontal and vertical control for construction projects. This network helps with site layout, design, and construction by providing accurate measurements of distances, angles, elevations, and positions.

The Art and Science of Jobsite Survey Control

Surveying control points: theodolite on a construction site

The process of setting jobsite surveying control points is a critical foundation for some construction projects. In some instances, tradespeople need to know, with high accuracy, where each of the elements they are responsible for installing are located in the real world. In this case, a land surveyor typically initiates this procedure by locating the existing structure and the property boundary and establishing control points around the jobsite. The surveyor will utilize survey monuments, physical markers indicating land boundary corners, geodetic control points, or local control points to establish these reference points.

After setting the control points on the exterior, they’re carried inside the building as axis lines, which are common forms of control points within structures. Architects often include these lines on their drawings, and their intersections form control points. Axis lines are usually parallel to the property boundary, with their spacing predetermined by the architect or other parties responsible for the project's design.

The design plans include dimensions from the axis lines to the elements being installed, such as walls. This enables carpenters and other construction professionals to know precisely where to locate these components in the real world. Control points effectively bind all the design plans from various parties, ensuring elements are installed in the correct location.

Given the crucial role of surveying control points in the construction process of some jobs, any inaccuracies can lead to costly mistakes and project delays. Therefore, it's essential to engage a licensed surveyor to establish control points and lay out axis lines on a jobsite. By following best practices such as utilizing geodetic control points or cadastral benchmarks, employing modern surveying equipment, and performing regular calibration, you can optimize the accuracy of surveying control points and ensure successful construction projects.

Determining the Need for Jobsite Survey Control

Surveying control points: engineers talking while walking together

Understanding when to leverage jobsite survey control can greatly impact the efficiency and accuracy of construction projects. Capturing controls during scanning provides numerous benefits, but it's essential to consider the end use of the point cloud and the specific construction scenario to determine the necessity of surveying control points.

One of the main reasons for field scanning is to capture existing conditions, which is especially critical in renovation projects where old drawings might not accurately reflect the current state of the site. Documenting control points allows the surveyed conditions to be accurately aligned with design BIM models or computer aided design (CAD) drawings, benefiting architects and design teams.

Reality capture also plays a significant role in coordinating different trades and verifying the correct placement of elements. Regular scanning and the use of surveying control points can prevent future clashes and streamline project coordination. While manual alignment is an option, leveraging jobsite survey control ensures a higher degree of accuracy.

Furthermore, in the past, surveyors would only capture the necessary insights for the specific task at hand, such as checking the elevation of a slab, using a total station. However, with the adoption of 3D scanning in the industry, everything around the slab, and not just the slab itself, is also scanned and represented in the resulting 3D model. This means that a wealth of data is captured other than what is immediately needed for the task. While this may not require the point cloud to be in survey control at the time, having control points can be very useful later on, especially if you need to extract additional information from the point cloud or make adjustments to it in the future.

When Not to Use Surveying Control Points

Engineer using a theodolite

Though surveying control points are integral to the accuracy and success of many construction projects, there are specific scenarios where they may not be necessary. Understanding when to leverage surveying control points and when it's acceptable to forgo them can help streamline your construction processes and optimize project outcomes.

For smaller scale projects or those with limited complexity, manually aligning the point cloud with the BIM model or CAD drawing can be a sufficient alternative to using surveying control points. This is often the case with residential buildings or interior fit-outs, which typically don't have the same level of sophistication as commercial and industrial projects. The reduced complexity of these jobs allows for a larger margin of error, making manual alignment a more viable option.

In addition to smaller scale projects, surveying control points might not be required if you're only comparing dimensions within the point cloud. For instance, when verifying measurements like window or slab openings, you can measure the openings directly from the point cloud and compare them to the design drawings. This method allows you to focus on the specific elements captured within the point cloud, without the need to tie them into survey control.

Another situation where surveying control points may not be necessary is during the initial stages of a project, when preliminary data collection is being conducted. In these cases, the focus is often on gathering general information and understanding the overall layout and conditions of the site, rather than capturing precise measurements.

However, it's essential to keep in mind that forgoing surveying control points should be carefully considered and done only when the potential consequences of inaccuracies are minimal. Incorrect measurements and misalignments can lead to costly errors, delays, and rework in the long run. As a rule of thumb, always assess the specific needs and complexities of your project before deciding whether to leverage surveying control points.

The Role of Technology in Surveying Control Points

Engineers controlling a drone

Modern technology plays a significant role in surveying control points, improving accuracy and efficiency. Some key advancements include:

1. 3D laser scanning: This technology captures detailed and accurate point cloud data, which can then be aligned with control points to create precise representations of the jobsite.

2. GNSS and RTK systems: Global Navigation Satellite Systems (GNSS) and Real-Time Kinematic (RTK) systems have transformed the way surveyors establish control points. These satellite-based positioning systems provide real time, highly accurate coordinates, enabling surveyors to determine control points and carry out other surveying tasks with unprecedented precision.

3. BIM and CAD integration: Integrating surveying control points with digital plans or BIM models enables accurate coordination, clash detection, and verification of construction elements.

4. Software solutions: Platforms like Avvir Inspect can help analyze point cloud data, identify deviations, and highlight potential clashes when control points are used, streamlining the construction process.

Unlocking the Key to Flawless Project Execution

Surveying control points are often essential for accurate and efficient construction projects, helping to ensure that all elements are built according to design plans. By understanding the importance of control points, implementing them accurately, and utilizing modern technology, you can minimize errors, save time, and optimize project outcomes. Although there are cases where control points may not be necessary, it's always better to err on the side of caution and use them whenever possible.

And the best part? Don't miss out on the opportunity to reimagine your construction projects with unparalleled precision. Embrace the power of Avvir Inspect and experience a new level of quality assurance in construction. The technology empowers you to automatically identify critical quality issues by comparing design intent (BIM) with actual site conditions (point cloud). As a result, you not only save time and resources but also help prevent costly errors and delays. Schedule a demo and see Avvir Inspect in action.

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