Fundamentals of Reality Capture- A Systematic Approach to As-Built Documentation
Ala Hamdan, PMP
Founder at OcuMap | C.E.O at Reality Imaging & Mapping Technologies | Advocate for Innovation in Civil Engineering
Unless you have been living under a rock, you must have heard of the term Reality Capture but what does it mean, who uses it, how is it done, and how do you benefit from it? This article will cover the fundamentals of Reality Capture and break down the different methods and tools used to generate as-builts for engineering purposes.?
Intended Audience:?
Before you read any further, the intended audience for this article includes Architects,Civil Engineers & Surveyors, Process & Mechanical Engineers, Construction Managers and Facility Managers.?
Definitions:?
Reality Capture : A method used to replicate dimensions, geometry and position of real-life objects (or the environment) with high accuracy, typically in millimeters to centimeters. Think of it as a digital replication of an existing building, facility, road, bridge, etc. that is needed to deliver an as-is or an as-built drawings for further engineering analysis and design.?
3D Laser Scanner : An instrument that emits a laser beam from a rotating mirror out towards the area being scanned, then distributes the laser beam at a vertical range of 300° and a horizontal range of 360°. The laser beam is then reflected back to the scanner by objects in its path. The distance to the objects defining an area is calculated as well as their relative vertical and horizontal angles. Laser scanning is a non-contact, non-destructive method of measurement.?
LiDAR: Light Detection and Ranging is an active remote sensing method that uses a laser to measure ranges (variable distances) to the surrounding environment. When the laser is combined with GPS and Inertial Navigation System (INS) data, a precise dimension, shape and location on Earth is generated in 3D.
Point Cloud :A set of data points in some coordinate system defined by X, Y and Z values that represent the surface of an object. Point Cloud data is the result of 3D Laser Scanning as well as LiDAR.?
Photogrammetry: GoogleEarth is a perfect example of the final result of photogrammetry but how is it done? Photogrammetry is the science of making reliable measurements by the use of photographs. It involves taking overlapping images then assigning a scale based on distance and focal length of the camera. Measurements can be generated from photogrammetry with various accuracies depending on how the data is captured. The accuracy of photogrammetry could be enhanced with GPS data.??
Reality Capture Tools:
Depending on the project requirements and deliverable, there are different tools available to capture reality, these tools include:?
Stationary 3D Laser Scanners: Also known as terrestrial laser scanners. These tools are used to document vertical structures such as buildings, industrial facilities and bridges. Stationary scanners are known to produce the most accurate measurements (point cloud data) due to the fact that they are stationary. These scanners emit laser in 360 degrees to cover the sphere around them.?
Handheld Laser Scanners: Used to scan (measure) smaller objects within close proximity such as a chair, a mechanical pump, valve, etc. Handheld scanners are useful where there is an access constraint where a terrestrial scanner cannot enter. They also emit laser directly towards the object being scanned instead of 360.
Mobile LiDAR: Typically mounted on vehicles including ATVs, Trucks, Railcars, Boats, Etc. Mobile LiDAR is coupled with GPS and INS in order to locate position and orientation of objects in it’s path. This tool is used to map corridors such as roads, railways, rivers, etc.?
Aerial LiDAR: When mounted on an airplane, it is used to map out larger areas such as cities, mountains, shorelines, etc. When mounted on a UAV (Drone), it is used to map out a tract of land, or a rooftop of a building due to limited time of flight. Aerial LiDAR is always coupled with GPS/INS just like the Mobile LiDAR.?
Aerial Photogrammetry : One or multiple cameras can be mounted on an airplane to take overlapping imagery with embedded GPS data. This can also be done using UAV (Drone) for smaller scale projects.???
Tools Matrix
Why is Reality Capture Important??
For any design, renovation or maintenance project, you need to capture existing conditions as a first step, however, traditional methods of surveying are time consuming, tedious, and provide the minimum amount of data, often leading to site revisits, cost and schedule overruns. In addition, as projects progress through different stages, different groups may need different information, Reality Capture provides a precise replica of the field and delivers a baseline to the desktop of the project team, eliminating confusion that may arise from piecing information collected at different times, by different people.?
For example, if we look at a conventional survey of an empty plot of land, you may notice elevation readings taken on a 1x1 foot grid. When compared to a 3D laser scanning survey, you can get readings in a 1x1 inch grid due to the millions of measurements taken by the scanner. A common good practice of Reality Capture is that a tremendous amount of data should be collected in the field, then dumbed down at the office depending on the requirements. Just because we can show a 1x1 inch grid, does not necessarily mean that the project requires that level of detail but the baseline information will be available should the need for it arise in the future.?
Use Case in Architecture?
According to the US. Energy Information Administration (EIA) , more than half of the commercial buildings in the US were built before the 1980s, that is 40 years ago. To put it in perspective, IBM released their MS-Dos computer in 1981. The challenge for Architects needing to renovate these old buildings today is that all drawings (if available) were done manually. Another challenge is that these buildings may have gone through major layout changes Internally and all of these changes are not shown on the old drawings.?
Let’s take for example a 3-story mixed use building that is about 70,000 square feet. The owner hired the Architect to renovate the exterior, change out the interior layout, and produce a master lease plan. The first step would be to know what is there, how tall, wide, where is it located, etc. This is where Reality Capture comes in to help. With a few hours of scanning, the entire building (every inch) can be measured and mapped, then data is taken back to the office for processing. Once processing is done, the pointcloud data is imported into Revit for modeling. The deliverable is a 3D CAD model (Revit) of the entire building including HVAC, Exterior, Interior, Structural, Electrical; and Plumbing. It is important to point out here that laser scanning can only measure what the laser hits, it cannot see through walls for example. Other Architectural use cases are listed below.??
Use Case in Engineering (Civil, Process, Mechanical)??
As previously mentioned, as-built documentation is the first step in any design and maintenance project. Civil engineers for example need a topographic survey of a site to determine drainage. Another example is the use of Reality Capture in locating defects along a reservoir structure, all of which can be efficiently done using 3D laser scanning techniques.?
Process and Mechanical Engineers might have a need to as-built an existing pipe rack, valves, furnace, etc. Drawing these equipment by hand is extremely time consuming and inaccurate. Laser scanning can document pipe dimensions and layout with spatial accuracies up to 2 mm. Isometrics and P&ID can then be generated from the pointcloud data Other use cases are listed below.?
Use Case for Roads and Railroads?
How do you Capture Reality??
While there are different ways, tools and methods used to capture reality, for the purpose of this article, I will only cover the terrestrial laser scanning and mobile LiDAR for brevity.?
Capturing Reality with a 3D Laser Scanner?
Capturing Reality with Mobile LIDAR System?
Conclusion?
Reality Capture is a method used to replicate existing conditions with high accuracy for engineering analysis. It will become the norm for documenting as-builts in both vertical and linear projects. There are different tools that can be used for reality capture and selecting the right tool will depend on the project requirements. Project teams will realize immediate gains in quality and efficiency, and will ultimately realize cost savings over the lifetime of the project.?
About Reality IMT
Reality IMT applies the latest imaging and mapping technologies to document existing conditions and generate highly accurate as-built models in 3D CAD. More info is available at https://realityimt.com ?