Cool, a Point Cloud… Now What?
3D Scanning has become commonplace on many projects, and can save hours of field verification. It can also add layers of complexity, confusion, and frustration if not executed properly on a project. Many people know what 3D scanning is, but not everyone is as versed in working with point clouds downstream. The most basic 3D scanning applications can become counterproductive simply because not everyone understands what the data is, or how to use it for optimal productivity.
Let’s look at the most basic items to check off the list prior to diving into a point cloud.
Can the Computer Handle the Data?
It may be perplexing to some folks that in 2017, design teams would have insufficient computing horsepower to effectively utilize point cloud data. Unfortunately, project teams are still met with the lack-of-power dilemma. There are many scenarios that can inhibit the use of a 30GB file, including the time and bandwidth needed to transfer large files or improper graphics drivers, which can be troublesome when loading or viewing data.
Municipal employees are usually 2-3 years behind on their computer hardware (and that’s being generous). One simply cannot function on a computer with 4GB of RAM and an integrated graphics card when working with point cloud data. All participants loading a point cloud of medium size or larger need some horsepower on their desk. Standalone graphics cards are a must. Most use NVIDIA, but if not, the card should support Open Graphics Language (Open GL). Many scanning programs will not open more than one view without an Open GL card on board. Again, this may seem fundamental, but it is a common problem that leads to frustration. Hardware problems can be avoided by checking this item off the list up front.
In the event that a hardware upgrade is not feasible, arrangements should be made up-stream for another project participant or consultant to convert the data into an Autodesk model. The use of “Regions” in ReCap will create layers within the point cloud that can then be toggled in Autodesk® Revit®. Less data loaded allows for more fluid movement and far less frustration. Also consider segmenting the project floor by floor to manage file sizes in multi-level projects.
Speed things up with Worksets
For additional control, it is helpful to place each point cloud on its own workset. This enables additional visual and project stability support. When opening the model, the user can specify what worksets (point clouds) should be turned off/on when opening a large model. Revit 2017 and updated 2016 now have the “unload for me” option; however it can still be helpful to manipulate linked models including point clouds via worksets. My favorite is the workset option “visible in all views,” helpful if turned off for large, sluggish, linked models.
Figure 1: Some of the workset ideas and options available
What Coordinate Systems Will Be Used?
Too often a project is already underway when the need for 3D scanning arises. At this juncture, the point cloud needs to be incorporated into the existing model or vice-versa. This is not a problem if everyone coordinates the scanning effort and has an understanding of what will be delivered. Surveyors and engineers generally dislike the use of 0, 0, 0 coordinate values, which is opposite members of the construction community, who generally prefer a close origin. This task will not be a problem with solid communication across the project team and an agreed-upon solution. Surveyors can use both their coordinate system and the project team’s UCS if they know how to utilize and export data on an alternate UCS. Once the model is dragged or rotated into place manually, a valuable benefit of 3D scanning has been lost. Knowing the difference between XYZ and NEZ when communicating with the rest of the team regarding survey control is critical. Again, this may seem basic, but it happens more than one would think. Asking proper questions in this scenario will reduce reworks and ultimately make for a smoother scanning process.
Figure 2: Export image from JB’s initial brain dump
What File Format Will Be Used?
Many people may be scratching their heads on this one. It has to be an .rcp or .rcs, correct? The short answer is yes. The data will ultimately need to be in .rcp/.rcs format to be imported / attached in Autodesk products. But where did the data originate? What kind of scanner was used to capture the data? The difference becomes apparent when the ReCap files are created. Point Clouds have properties. These properties include XYZ values, RGB values, intensity values, and last but certainly not least, normal values.
The normal value of a scan point specifies the direction from which that point was captured (this is Adam’s favorite view option which often helps differentiate faces of an object). Depending on which file format was converted, some (or multiple) properties may be lost. Different formats may contain some or all of the scan properties. When exporting point cloud data, there is usually an option to include or omit particular properties/attributes. The data is most useful when a point cloud contains all the properties.
Often, Autodesk will not snap to a surface without the normal values. Some file formats can be exported both ways. For example, an e57 file can be a single (unified) file of an entire project, or can be individual scan stations. A ReCap project with individual scan stations will provide station-based views in ReCap which are displayed as “Mirror Balls” in the software. Double-click a mirror ball, and a station-based projection opens, which may provide a favorable view of items in that area versus navigating in 3D.
Figure 3: Example of “Normals” point cloud visibility option. Image courtesy of TITAN, AEC
Before You Start Modeling Existing
A few questions to ask: Who will be using this model and what will they be using it for? Can you speak with the folks wanting to use this model or do you have to go through the formal channels? Do you have existing drawings? If existing drawings are not provided, it is highly recommended that they be acquired, preferably as electronic scanned image files. This can save valuable time, especially if you are modeling existing structures (you do not want to be guessing sizes). If other team members are also utilizing the existing drawings, discrepancies and/or findings can be notated on the electronic drawings so that As-Built conditions are documented and shared.
It is highly recommended that trade partners compare “As-Built” / or AutoCAD® DWG / or other Revit Models to the point cloud before AND after modeling for comparison purposes.
Figure 4: An image of a point cloud that has not been properly coordinated with the model. Don’t let this happen to you!
Now the Point Clouds, Grids, and Levels Are Established in Revit
You’ve received signoff from the team... now it is time to rock–n-roll. I was extremely fortunate in that my first experiences with Point Clouds in Revit were with the technical specialists at TITAN AEC http://www.titanaec.com/. It is vital to bring on expert consultants early to assure a successful Point Cloud experience.
Explore and Understand Visibility Settings
While working with Point Clouds, it is extremely important to be very conscientious of your view range. Rotating a section 90 degrees in elevation so that it is looking down creates a section that mimics a plan view. The location of a section cut or its view range can now be quickly adjusted.
A view can be set to wireframe and structural elements assigned a solid fill color with a 33 percent transparency. Play with these settings to improve the point clouds visibility as you’re modeling.
Strategically placed and named section views can save tons of time. A view along a beam line may be named with the associated gridline such as: LVL03-GRIDB. A section with a view range extending just shy of one gridline to another may be named: LVL02-GRID3-4 or something of the sort—plan your work and work your plan.
Learn a Little about ‘Geometric Dimensioning and Tolerancing’ (GD&T)
“There is no such thing as perfection.” “Nothing is built perfect.” “Perfect 90 degree angles do not exist.” Sound familiar? These words of wisdom are passed down from mentors to students all over the world. It helps to learn a little MIL/ASME/ANSI Drafting Standards, such as my favorite: Y14.5 GD&T. As construction becomes more "fab" based, the AEC industry will start to see more metric design drawings and/or callouts. Understanding designs in metric with GD&T can help document and explain these construction tolerances.
Floors Are Not Flat, Walls Not Parallel and Slightly Leaning. What Do I Do Now?
Upon close inspection, Revit levels will look off a smidge from the point clouds in some areas. As you explore the point cloud, you may notice walls are not parallel to each other that should be, or walls not perfectly perpendicular to the floor. Depending on the material type and age of the building, these anomalies may be better or worse depending on multiple conditions. Building elements expand and contract with temperature variations. While thermal movements will influence the position of building elements, their actual as-built location, including flatness and inclination are more likely a function of construction tolerances.
Serious doubts will be cast on the accuracy of point clouds, including but not limited to the good ol’ tape measure check comparison from the field (another reason to understand what the Revit model will be used for and have open communication with team members). If your team decides to go beyond “design intent,” some decisions will have to be made to deal with critical construction tolerances. Are we only trying to coordinate new MEP with existing structure? Are we tight for ceiling space and trying to squeeze mechanical ducts below an existing sagging slab and above a future dropped ceiling? Are we scanning the slab to check for floor flatness or level?
The question may come: “Why is it when we compare our dimensions from the field tape measure to your Revit model generated from a point cloud, the dimensions are off 3/4?” Using the dimension tool in ReCap and snapping dimensions in various places along parallel walls will result in many dimensional differences depending on whether measurements are taken on the ground, waist high, or above your head. Is this measurement snapped from the middle of the wall, near one end or the other? All snapped dimensions are going to be off slightly from each other. Nothing is perfect, straight, parallel, or exact.
What Does Your Contract Specify?
If the project you are helping with has a BIM Execution Plan, review and learn the model progression specifications, if necessary. All team members should have access to the point cloud when comparing to the Revit Structural model. All design teams and trade partners should have the same access and ability to turn on those point clouds to check critical field conditions visible from the point cloud that should be addressed and/or reviewed.
How Do We Want to Address Deflection?
Revit does not easily model a sagging beam or a deflecting slab (although that would be a fun adaptive family to make analytically correct with an engineer). Columns may twist and walls may be skewed that are supposed to be parallel. These are all red flags to share with your structural engineer team ASAP. Depending on various circumstances, the team may want to start identifying areas that exceed anticipated deflections.
By creating a search parameter that looks within the “comments” family instances to contain the word “verify” or “deflection,” findings can be scheduled, tagged, and quickly shared by also using a view filter and view template. For example, highlight extreme deflecting beams red and use blue for questions. This can greatly cut down time spent creating 2D Plans with associated 3D views to help tell the story.
How Can the Point Cloud Save the Most Time and Money?
Most likely, whoever purchased the point cloud already has specific items in mind. This question really depends on whom you’re asking, and when the data was captured. The entire design and construction team can benefit from aligned point clouds that are coordinated, delivered early and also at strategic times during construction.
Figure 5: Good example of Point Cloud Integration. Image courtesy of TITAN, AEC
Communication is the key to successful BIM. Don’t be too afraid to ask questions!
Jordan Banning is a Principal at CSDS Inc., a California-based Engineering & Construction Supply firm that provides a wide range of technology products and services to the AEC Industry. Jordan has 15 years of experience in the construction and geomatics industry and has consulted on numerous projects ranging from civil to vertical construction and engineering. Jordan has a B.S in Business Management from CSU Sacramento.
Adam Muñoz is a BIM Technician with Buehler & Buehler Structural Engineers, Inc. He is CM-BIM certified, a Revit Structure Certified Professional, and an AutoCAD Certified Professional. He is a Professional AUGI member and has authored five previous AUGIWorld articles. Adam enjoys collaborating with others who share his passion for research, development and training, and sharing his knowledge with project teams.