Learning Objectivesaucache.autodesk.com/.../class_handouts/v1_AB5602_Cone.docx · Web viewYou can reduce your daily rate by working with companies that use less current equipment,

Laser Scanning to BIM: If You Look at It Long Enough You Might Model SomethingKelly Cone – The Beck GroupKyle Bernhardt – Product Line Manager for the Building Design Suites

AB5602 Whether it is for developing existing models, as-built data collection, or installation verification, those millions of colored dots sure do get a lot of hype. In this class we'll cut through the chatter and misinformation out there and cover what you need to specify to scanning providers, how you can justify the up-front cost with project ROI information, and finish up with how you can actually use all those little colored dots to create models in Revit. There are a lot of high-tech options out there for automating part of this process, and there is the tried and true manual process as well. We'll cover the pros and cons of what's available to you today so you can make your next Laser Scanning project a blockbuster. Take the red pill, and step into the dot matrix...

Once you've taken the Red Pill, you'll need some training to be the One at your firm who understands how to work with all this point cloud mumbo jumbo. Starting out in Revit, we'll talk about how to link in point clouds (and what the pitfalls are) and best practices and tools for modeling in your new virtual reality. We'll also introduce you to some plug-ins that let you do a lot more when modeling than Revit can natively. We'll bridge the paradox of modeling too detailed, or too generic. And, finally, we'll take a quick spin in Navisworks to help you understand that sometimes you don't need to model everything, and make you jump off a building or two while we're in there. (Don't worry, you won't get hurt, we'll have collisions turned off...). If you can make it through the training, you'll be ready to take on anything.

(If you noticed this is a little different than the class catalog, good eyes! Myself and several of the other scanning lecturers conspired to make sure we didn’t cover the same things multiple times, or miss critical information. Since this class is one of the first, we all felt it would be more advantageous to cover some additional basic information, and leave some of in-practice examples - like walking through the steps to link a file into Revit for instance - to classes later on in the schedule that have to cover that information anyway. I understand it doesn’t exactly match the description on AU’s class scheduler, but we felt this would better serve those most interested in scanning and taking several scan to BIM classes. Hopefully you agree! If not, well, that’s what surveys are for. Thanks, and see you in class.)

Learning ObjectivesAt the end of this class, you will be able to:

Understand and specify LOD and shadowing requirements for Laser Scanning providers.

Understand what drives the cost of Scanning so you can target your specification to meet your project budget.

Describe the ROI benefits of Laser Scanning.

Understand how to work Laser Scanning into your project schedule on renovation projects.

Describe the various tools and techniques for using point cloud files to generate BIMs.

Understand the advantages and pitfalls of simplifying the point cloud to a BIM.

Laser Scanning to BIM: If You Look at It Long Enough You Might Model Something

About the SpeakerKelly Cone is the Innovations Director at the Beck Group, an integrated Development, Architecture, Construction, and Technology company headquartered in Dallas, TX. Since receiving his master's degree in Architecture from the University of Texas, Kelly has been focusing on the implementation of BIM across integrated disciplines. This covers a wide range of software including Autodesk® Revit®, Navisworks®; Innovaya, Synchro Professional, and DProfiler™, our own in-house macroBIM application. The implementation process includes the creation of customized design-build-oriented content and the alignment of costing and scheduling assemblies to that content. Kelly plays an integral role in representing Beck's BIM capabilities, attending and speaking at numerous conferences and teaching classes about BIM. He is also heavily involved in the BIM community at large participating in the AUGI® Revit forums and through the Web site, www.bimexpert.com which he co-founded. Kelly also recently started a blog called Revit Futures devoted to building community support for pushing dramatic changes to the Revit [email protected]://revitfutures.blogspot.com/

What is all this Laser Scanning Mumbo Jumbo?So, what is all this scanning stuff about? What’s it all for? Plus, what’s with the terminology? Point clouds, shadowing, LOD, artifacts, etc… There’s a lot of info to sift through before you can master this bit of virtual reality. Hopefully this class will give you the confidence and knowledge to give it a good solid shot on your next project.

Scanning and Reality CaptureScanning is actually a subset of a group of technologies generally referred to as “Reality Capture”

Reality CaptureReality Capture is all about bringing the real world to the digital one. It is the inverse of the computer aided fabrication movement which is, of course, all about bringing the digital world into the real one. Reality capture encapsulates a number of technologies that have been around for decades. Photogrammetry and Videogrammetry are methods of capturing 3D information from 2D photographs. Photo Scene Editor, Photosynth, and Image Modeler are three examples of software solutions that leverage overlapping photos to generate 3D models from a bunch of 2D overlapping images. These are generally referred to as passive capture techniques because there is no device generating the light (or other source) through which the data is collected.

Passive capture solutions have some advantages (speed, cost, familiarity) but have some big shortcomings (accuracy, ambient energy, variation from capture to capture).

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ScanningScanning can loosely be described as any active scanning reality capture solution. Scanners generate laser light, sonar, x-rays, radio-waves, or other energy waves and harness the return energy to determine information about the objects around them. For AEC, most of what you’ll run into are laser based scanning systems. These scanners typically use a combination of photos and the internal laser to capture all the data about the world around them.

Scanners like this are considered line-of-sight systems, which means they don’t capture information you can’t see from the scan position. This is a limitation of the energy spectrum, not the technology, but it drives a lot of the cost and feasibility considerations.

Scanners are either line of sight or phase based, and this refers to how the scanners capture the distance information. Line of sight scanners record the amount of time it takes for a flash of light to leave the scanner, hit the surface, and bounce back. This, combined with the speed of light, allow you to calculate the distance from the scanner to the surface. Phase based scanners use a continuous laser beam and utilize the phase of the returning light to calculate the distance. Once you have distance, it is just a matter of azimuth and rotation and some triangulation to figure out the exact X,Y,Z coordinates of the surface.

Scanners can also be placed onto moving carts or vehicles, although this has a significant impact on accuracy. Mobile Scanning is popular in the civil infrastructure world because accuracies in the +/- 3” range are perfectly acceptable. The degradation comes from the level of accuracy of the measurement determining the exact position of the scanner as the measurements are made. Mobile systems use a combination of survey points, GPS, and an inertial measurement unit (IMU) to calculate the position of the scanner at any point in time. The error present in the IMU/GPS combination is what decreases the accuracy of mobile scanners. If your use-case is fine with mobile scanning accuracies, it may be a much faster way to collect data along a path.

Understanding and Specifying Laser Scanning.One of the biggest challenges with Scanning is asking for the right thing. Like any other service, communicating clearly what your expectations are is critical to getting what you want at a price you can afford.

Critical ItemsThere are two approaches to specifying scanning or reality capture services. One is to specify all the minutia and deliverable, the other is to specify the end uses and deliverables.

AccuracyAccuracy is a touchy topic that can easily get derailed with discussions on tolerance and error. Without getting into a philosophical debate, there are three critical areas where you need to pay attention to accuracy requirements.

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The first is the accuracy of the actual scanners being used. Time of flight scanners typically get close to +/- 1/8” at 100 meters while Phase Based scanners are closer to +/- 1/8" at 50M. Scanners become less accurate the further from the device you go as the laser spot gets larger and the mathematical error increases over time. Most scanners fall within this range. Noise is something that can impact scanning accuracy, although most major brands are also within acceptable limits.

Second is what is called registration error. Due to the technology being line-of-sight, scanners must be set up in multiple positions to reduce shadowing (empty places in the scan data not seen by any of the scan locations). All the data collected at each point is susceptible to only the device’s own error. However, each location must be registered to each other location, and since there is inherent error in the individual measurements, there is always some error present when registering the data. We typically like to see registration error on the order of ¼” to ½”. Anything larger is usually symptomatic of poor surveying work during the scanning process or of registration mistakes during processing. This is why we insist on licensed surveyors on our scan crews.

The combination of these two error sources give you what is referred to as relative accuracy. You can determine the potential error of measuring between any two points in the entire point cloud by referencing the relative accuracy of the scan file.

The third note is to not ask for the impossible. Please keep in mind that buildings are not as static as we like to think. Buildings are in constant motion due to physical or thermal stresses being placed upon them. Buildings can get shorter and taller, or shorter and longer due to the temperature differential over the course of a day. Taller buildings may move several inches or even feet due to windy conditions. Scanners capture what is present to a high enough degree of accuracy for these changes to be measured. Don’t mistake them for errors in the scan data. If your use case is critical enough to require precision beyond what these kind of movements would allow, additional steps need to be taken (scanning only at certain temperatures, or in certain wind/weather conditions).

At the end of the day, you need to specify an accuracy that meets the needs of the use case for collecting the data. If you don’t need +/- 1/8”, don’t ask for it as this will dramatically increase your costs.

LODThe Level Of Detail requirement for scanning is basically a way to define how dense the scan needs to be. Keep in mind that scanners work off a polar coordinate system, so spacing is determined by what fraction of a degree the scanner spins before capturing the next row of data. So, spacing is always specified at a given distance. 1” by 1” at 100 feet is a relatively tight measurement for a time of flight scanner for instance. That same spacing will give you a tighter density at 50 feet, and a looser density at 200 feet. As you might have guessed, specifying a density at a distance is one way to make this requirement.

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The GSA uses something called Artifact Size which specifies instead the size of the smallest object that needs to be captured by scanning. Specifying a 6” artifact means items larger than 6” would have sufficient points on them to make out what they are, while items smaller than 6” like hanger rods would not likely have sufficient points to make out.

You can also specify minimum point densities, although this is much harder to measure (verify) and to deliver. Again, ask for what you (and your project) need, not the highest available.

ShadowingSince laser scanning is line of sight, if part of your space is obscured by a wall or a beam you’ll need an additional scanning position to capture data on the other side of that object. Some basic rules of thumb:

Square or rectangular rooms require at least two positions to fully capture. L shaped spaces require 3 positions. Overhead conditions with a lot of relief (complex ceilings or exposed MEP) will require

many more positions to fully capture. Sometimes the height of a scanner is important. For a complex ceiling placing the

scanner on the floor instead of on a tripod can cut the number of required positions in half as you increase the angle of incidence to the ceiling plane thereby reducing shadowing from surface relief.

Shadowing is one of the biggest mistakes for first time scanners, and one of the biggest cost drivers for service providers. Specifying 0 shadowing means a room might need 15 setups to capture, while specifying 5% shadowing might allow that same room to be captured in 3 to 5 setups. That’s a 3 to 5 times cost increase for a minimal amount of data.

File FormatsMost point cloud tools out there support multiple file formats for import/export. We typically request files in either PTS or PTX format, although LAS, FLS, and TXT are other common formats. As always, reference your software of choice to see what you need to work with.

For reference:

Revit

FLS FWS LAS PTG PTS PTX XYB XYZ

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Navisworks

ASCII Laser (ASC,TXT) FARO (FLS,FWS,iQscan,iQmod,iQwsp) LEICA (PTS/PTS) Riegl (3DD) Z+F (.ZFC,.ZFS)

You should also consider whether you want scans delivered as individual registered scans (15 scan locations = 15 different files) or bundled as a single point file (1 giant file). Each approach has plusses and minuses that vary depending on the software you’re using.

Additional Point DataMost scanners can also capture photographs as they scan, or high end cameras can be used with special mounts to capture higher resolution, higher fidelity, or HDRI images from the scan location. These photos can be used to map colors onto the individual points. Most scanning formats support x, y, z, intensity, R, G, B values for each point. Photo mapping colors to the points can make them much easier for people less familiar with scan data to recognize features within the scans.

You can also use these colors to map other information into the point cloud file. Anything you want to visualize with color can be used to create the RGB values. Thermal imagery? Check. Z distance at a scale? Check. Some software tools can automatically map dimensional filters on top of point data, but neither Navisworks nor Revit can do this, so you have to write that data to the point cloud file to see it in either application.

What will you do with it?At some point, laser scanning is not an intellectual exercise. You’re intending to use it for something. Ultimately, the use case drives the deliverable. If you’re working with a scan provider familiar with the AEC market, you can often times use just the use case combined with the deliverables to specify a scan. Instead of stressing over all that LOD, Shadowing, and Accuracy stuff, write down what you want to do with the scans.

Are you going to use it as a basis of Design? Or as a basis for Construction? Are you going to model objects from the point cloud? If so, what is your tolerance on

those objects? (Walls +/- ½”) What all do you want to model? Switches? Fixtures? Hanger Rods? Are you trying to fabricate anything using the scan data as an existing conditions

measurement tool? Who all will use the scan? Client? Design Team? Contractor? Subcontractors? What programs are you taking it into?

The more information you can provide, the better the service provider can tailor the end product to your needs. Also, don’t forget that you might not be the only one who can use the

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scan. Talk to the Architect or Contractor you’re working with. They might be willing to split the cost if they can also use it for their purposes. Don’t forget the Owner for that matter.

DeliverablesRegardless, you will always need to specify the deliverables. Raw data is useful if you ever want to combine the current scans with more. Processed data (typical file formats listed above) is the primary deliverable in most cases, although format and number of files needs to be specified. Most scanning providers can also offer additional deliverables spanning from web-based viewing options to animations to modeling.

Modeling in particular may be something to ask for some help with. Many of the automated tools to extract simplified geometry from point clouds cost tens of thousands of dollars. It may make more sense to have your scanning company extract topography, civil components like roads and sidewalks, or even building components like pipes and duct using some of these high end automated tools. One thing to watch out for is to make sure the end result of these tools are usable in your application. Pipe created in Edgewise Plant will not magically become intelligent pipe objects in Revit, a least not yet.

If you’ve never worked with scanning before, make sure you’re working with a scanning company that is familiar with the AEC market and can help guide you to asking for the right things.

What makes Scanning cost so much?

Cost DriversThe major cost driver in Scanning is time. Scanning companies are service providers, and the man hours required to deliver a scan are the majority of the cost. Equipment costs, mobilization and travel are the other obvious factors that influence costs. Anything that increases the amount of time required, increases the costs proportionally.

Over SpecifyingOver specifying is the number one killer of scanning projects. Writing an impossible or extremely difficult specification can increase the cost of scanning on a project by a factor of 10. A great example of this is some of the early GSA contract language for scanning that required 0% shadowing. This single requirement took the cost of scanning a relatively small project from around $15,000 to $150,000. The first rule of scanning is ask only for what you need.

The ScanThe scanning process itself is time intensive. Most scanning crews are two or three people. The scanner is a heavy piece of equipment with large batteries, and is usually tethered to a laptop. Depending on whether it is a line of sight or a phase based scanner, a single scan will take between 15 minutes to over an hour, or between 5 and 15 minutes respectively. There is

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some setup and breakdown time between each scan as well. We typically see productivity in the range of 10 to 15 scans per day on time of flight systems, and 20 to 30 scans per day on phase based systems (assuming an 8 hour day). The higher the density of the scans, the lower the productivity will be (each scan will take longer). If you can scan an entire job in 10 time of flight scans, you can probably get it done in one day with reasonable density requirements.

As you can see, the time on site scanning is all driven by the number of scan setups required. This is why it is most common for contractors to try and scan after demolition is complete on renovation jobs. A project might take 100 scans before you rip down all the walls. Once they’re down and you only have the building core left, that same job might take only 20 scans. Plus, you’ll get all the stuff above the ceiling you’d have missed in the pre-demo scan (unless you started scanning between the ceiling and the structure which might take the number of scans to 400 for the same job). At roughly $4500 per day @ 10 scans per day, that’s the difference between $9,000 dollars, $45,000 dollars, and $180,000. Time, and timing, is everything…

You can reduce your daily rate by working with companies that use less current equipment, or don’t have licensed surveyors in their field crews. However, if you find errors in your scan the scan is basically worthless till those are resolved. The #1 reason scans are bad is due to surveying errors in setting up the scan locations. We never use companies that don’t have licensed surveyors for this reason. We’d rather pay 4500 per day for something we can trust than 3500 per day for something we won’t use at all.

ProcessingOf course, once all the data is collected it has to be registered, cleaned up, checked, etc… This is called processing. A general rule of thumb is that processing takes twice as long as scanning. So, if you scan for a day, it will take two days to process all that data. Processing can be done as scanning continues, so you can reduce the impact of processing on longer jobs by processing the first day’s data while the remaining scans are being collected.

Why does it take so long? Well, a single scan can be well over a GB in data. Processing that much data takes some serious horsepower and some serious time. Plus, your service provider will use a number of processes to load the data, check it for errors, clean out noise in the data from people or cars walking by, or from rain or fog for that matter, and then register it all together and check for registration errors.

Mapping photos to points also incurs a processing time. Photos many times have to be manually stitched to the point cloud data. This can add up to a whole additional day to the processing time depending on the photo format and the software the provider is using. Scanners using their internal cameras will often automatically stitch photos, but the quality of the built-in cameras is frankly terrible. Your cell phone has a better camera than these $30,000 scanners do.

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Some software tools are beginning to automate certain steps of this process which may reduce the amount of time required. However, these solutions are making small increases in efficiency possible; but they aren’t knocking days off of processing time yet.

Post ProcessingPost processing is used to refer to additional manipulation of the point data. So, if you want the service provider to provide a TIN file of the topography captured in the laser scan, that is considered post processing. Most post processing charges are a result of additional modeled deliverables outside of the scanning process.

What makes it worth it?So, what makes it worth all the hassle? It sounds expensive, complicated, and hard to use. Why bother?

Saving TimeSometimes you have to spend some time to save some time later. Scanning is all about saving time. Once a scan is complete, there are so many things you’re used to doing on projects that you shouldn’t have to do anymore.

Measure OnceMeasure twice, cut once. We’ve all heard it before. I prefer to measure once and measure right if it’s all the same to you. The beauty of scanning is that you take one “measurement” and effectively capture millions of individual measurements. No need to run that measuring tape or disto a second time. No need to write down the dimension on a pad and hope it makes sense later. No need to worry about spilling coffee on your pad and wiping out a day’s work. (Although, you do need to worry about spilling coffee on a laser scanner that probably costs more than you make after taxes in a year!)

Make One TripWe’ve all been there. You measured “everything” on that site visit but somehow missed that one critical dimension that your job now depends on. Yep, make another site visit…or not. Scanners capture anything and everything they can see in one go. Presuming you did a good job specifying the scan, getting that measurement you need is as simple as opening the model and using the dimension tool. No more second, third, fourth, fifth, of fifteenth site visits for you…

Work off the same informationDon’t you just love it when your consultant or sub went out and measured one thing and you measured something else, but you don’t find out about it until none of your documents or coordination models match up? Neither do I. Part of the error in measuring anything is that each person measures things differently. If you’ve got 15 different people doing field measurements, you’ll get 15 different measurements. Those kind of errors can really kick your

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backside if you’re relying upon them for coordination or fabrication. A scan lets you work off the same dimensional information and backgrounds as your consultants and subcontractors, and eliminates a lot of time arguing over whether it is 15’-1” or 15’-1 ½” between those two columns…

Saving MoneySaving time saves money, but sometimes that isn’t enough. Scanning can flat out save money over traditional methods in a lot of situations; you just have to look at it the right way…

Pay for One MeasurementScanning always seems expensive because it is treated as an additional requirement in most cases. However, every Architect, Consultant, Contractor, and Subcontractor has money in their budget for measuring the existing conditions on any job. Effectively, our clients are already paying for 15 different companies to take 15 different sets of overlapping measurements.

Scanning allows you to basically replace all that mess with a single line item that has no overlap. I’ve yet to find a reasonably specified project where I couldn’t pull a small portion of the field measuring budget from each stakeholder and completely pay for a scan. The biggest challenge to do so is to get all the stakeholders to own up to how much they have in their budgets for this work, not in ending up with enough money for the scan.

Saving MistakesSaving on mistakes is another benefit that usually makes scans pay for themselves, although this is always hard to quantify as it usually falls under cost avoidance.

You Don’t Know What You Don’t Know You Need To KnowAs confusing as that sounds, I think it is right. In other words, when it comes to measuring as-built or existing conditions information, you rarely know exactly what you will need measured once everything is said and done. Whether it is a critical measurement you didn’t take, or an entire scope you didn’t bother measuring at all, traditional surveying and field verification is frequently a repeated or continual process throughout a job. This is a result of not knowing more than anything else. Scanning won’t solve the knowing part, but by measuring everything visible, it makes the penalty of missing something much smaller and simpler to solve.

Assume Makes An… well, you knowLike the saying suggests, assumptions are the root cause of so many collisions or other field issues. Any time something is not measured (see above) we all have to make assumptions on what the dimensions and locations of those things actually are. How many times have you been privy to this conversation: “Did you measure to the bottom of the beams? Well, no, I didn’t think about that. We’ve got the structural framing plans after all, can’t we just model them where it says? Sure, they’re steel after all. What about fireproofing? Well, it was built 15 years ago, and the pictures make it look like spray on. It’s probably about 2” thick. Ok.“ There are a lot of assumptions in that relatively short conversation. What if the steel erector used different sizes to save cost? What if the fireproofing is thicker? Thinner? What if the FTF height in the

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documents is wrong? Etc… Those kind of assumptions can make or break a 12’ ceiling height. A scan makes it all go away: “Did you measure to the bottom of the beams? No, but let me pull up the scan. It’s 13’ 9 143/256”.” Done (with an absurdly accurate number just for laughs).

The biggest challenge: Scheduling?

The dilemma:On many renovation projects, the major barrier to scanning isn’t cost, it’s schedule….

After DemoIdeally, you always want to scan after any demolition has taken place. This reduces the number of scans and thus the cost, it reduces the amount of scope that shows up on your monitor but isn’t actually there anymore, and it exposes scope that is there that would otherwise be unseen. There is almost no reason to scan before demolition, unless you have no other choice…

Before Coordination or ModelingUnfortunately, scanning often times can’t happen at the ideal time. If your construction schedule has you installing scope immediately after demolition is complete, you have a major sequence problem. Scanning should be done after demo, but it must be done before coordination is complete. Coordination takes weeks, which means to get the best of both worlds you have your jobsite sitting demoed and idle for up to a month (or even longer). That’s a problem…

Some Tricks to Get Around itObviously, we don’t want to throw out a good tool because we’re not smart enough to figure out how to use it. There are several tricks you can use to try and make it work…

Schedule for it. No really, it’s that simple. If you can, work scanning into your schedule from day 1. If everyone is expecting it and understands it, no one will think you’re an idiot for leaving a space demolished out for 6 weeks. They’ll think you’re a genius. If you can’t schedule for it, try getting creative…

Can you do a partial demo (remove all the ceiling tiles 6 weeks early)? Can you partially coordinate each area and save one last coordination meeting for the

scan coordination thereby reducing the penalty from 6 weeks to 2 weeks? Can you phase your installation scope so that items not depending on overhead

coordination can go in while the overhead stuff is finishing up in a coordination meeting?

Can you selectively demo some typical spaces in advance to help at least refine your assumptions and improve the coordination model?

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Turning Point Clouds into BIMs.

Red Pill / Blue PillThere are really just two ways to make a BIM from a point cloud. One way is to manually create BIM objects using the point cloud like a background. The other way is to automate the creation of objects by analyzing the point data and having the software make some intelligent guesses. Again, there are plusses and minuses to each approach.

The Manual WayRocking it old school is the simplest way to go. No additional software or training required, total control over the process, and as fast/slow as your modelers. This is really no different from tracing from CAD files or importing a 3D model from some dumb modeling program (Not BIM). It looks different, and some of the “tracing” tools may be different, but at the end of the day the process is more or less identical.

Automation OptionsAutomated modeling, also known as feature extraction, basically works by trying to superimpose known shapes onto the point data, or by trying to extrapolate a shape from a set of point data. Examples of each method are readily available.

Scan to BIM (Imaginit) for instance uses a region grow to try and extrapolate a planar surface from selected points, and then allows you to map a wall onto that planar surface. It does a similar extrapolation for pipe or round duct. Edgewise uses a similar process to try and extrapolate both planar and circular surfaces from point data, although it attempts to batch process the entire cloud rather than have the user initiate each process one at a time.

Other tools such (mainly in the Civil space) search through the point cloud for signatures, looking for points whose arrangement closely matches the object they should represent like trash cans or street signs. There aren’t a lot of tools like this for AEC yet, but you could easily adapt this process to finding all the light fixtures and sprinkler heads in a ceiling for instance.

In either case, automated processes have on big downfall to weight against the obvious upside of improved efficiency, and that downside is control. Whether you’re modeling manually or using automated tools, modeling from a Scan is inherently a process of further simplifying and reducing the accuracy from the real existing condition. Walls are never perfectly flat or perfectly vertical, but our BIMs are. Same goes for every other scope in the building. When you’re manually looking at each condition, you at least have a trained eye making determinations about the validity of those simplifications and where the sacrifice should be made. When the computer is the one doing it, you’d better hope that algorithm is a darn smart one. Otherwise you’re putting a lot of faith in a computer vision matching algorithm to do your job for you. As always, a key determining factor for me is what the end use will be. It may not depend on me having the walls exactly match the built condition, so some simplification may be fine. If it does, than some of the more automated tools are probably not the way to go.

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Taking it Scope by Scope, Phase by PhaseFor all things BIM, I usually find a scope-based approach is the one to take. Whether it is breaking up responsibilities on a design team or determining the LOD requirements in our BIM execution document, each scope usually needs some unique treatment. And, not surprisingly, time is pretty important too. The phase in which something is being used usually has some impact on what kind of data is available and how precise it needs to be. Scanning is no different.

ArchitectureBreak down your primary Architectural scopes and see if something things need to be modeled to a higher or lower standard. Some things may not need to be modeled with the point cloud as a background at all. In most cases, Architectural assemblies are somewhat custom so thicknesses vary and there isn’t really a kit of parts to reference or match to. Modeling of these components is somewhat loose by default, and unless you can scan both sides of a wall or ceiling you rarely know the actual thickness for instance.

Code also has a big impact on what you model most accurately. If you’ve got a wall that has both sides scanned, should be 3 5/8” thick, and one side is an office and the other a restroom, you’ll probably model the restroom side as close to accurately as possible to help make sure ADA clearances are met and let the office be the side with some error in it.

For this reason we usually model Architectural scope manually. There are some good tools to model portions of it automatically, but we end up having to check every single element anyway due to the above concerns and at the end of the day, it isn’t any faster and can often be slower to model this kind of scope automatically.

StructureUnlike Architecture, structural design is usually with some fairly defined parts. Steel is particularly dependable, and can more easily be automated. Concrete is more difficult, but is usually supposed to be somewhat nominal dimensions.

On the flip side, structure is often the most obscured scope, whether it is by MEP and Architectural elements or by fireproofing.

Manual modeling is pretty simple however, so it isn’t that big of a deal. If floor levels have been determined from the scan, modeling structural members to follow is relatively simple. Size and location can be easily determined from the scan, and the rest is simple in most BIM platforms.

MEPMEP is actually the hardest thing to scan, and the hardest thing to model. You usually have the most shadowing or partial scans of this scope. Fortunately, round shapes are some of the simplest to auto-recognize, so piping tends to get simplified. Piping is also available in standard sizes, making it easier to check against a catalog and end up with the right information.

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Rectangular ducts are harder as closure is not implied by a partial scan. However, some tools will use automated searches along with user input on sizes to make up for that shortcoming.

Manual modeling is a lot tougher for MEP than for the other scopes because a lot it slopes, or turns at odd angles, etc… These are things that reality handles pretty well while BIMs do not. Making a user go through and model MEP accurately using manual techniques is extremely tedious.

PlanningSince the required LOD is pretty low here, and you’re unlikely to be making any changes at the scale of individual pipes or fixtures, scan and modeling accuracy can be pretty low and still meet the goals of the phase. Mobile scans are good enough for this kind of work, and similarly automated extraction of even architectural components are more than good enough. You can think of modeling as having it’s own accuracy or tolerance. For planning, +/- a couple of inches from reality is probably just fine (unless it is square foot driven like GSA work).

DesignFor this phase I find it is necessary to do more scope manually the further you go into the process. If your end goal is CDs, the notes above by scope are applicable. If your end goal is DD documents and you are a design architect, you could probably get away with less. Most design level work has a modeling tolerance of +/- ½” with some exceptions around critical code driven spaces.

ConstructionIf the end goal is construction coordination or even fabrication, the you need a high degree of accuracy. Even something as simple as modeling a wall as vertical when it is actually .2 degrees off can make or break a prefabricated MEP rack going in a hallway. For this kind of work, modeling tolerances need to be +/- 1/8” or less. This is almost impossible to achieve with much simplification going on, so it drives you to manual modeling techniques in many cases.

To Model or Not to Model? That is the question!As Shakespeare sayeth…

Points can be useful on their ownSometimes, we get overly attached to our BIMs. Sometimes we just need a little PIM. (Point Information Model)

Clash DetectionPoints are actually relatively intelligent for a simple dot. They know where they are, they usually have some data about their reflectivity and color. That’s more than enough to set up some basic filters and run clash detection. Doing a retail retrofit? Why bother modeling the structure if

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you’ve got a scan? Just clash against the structure. In general, if you’re modeling something you’ve scanned for the sole purpose of clash detection, you’ve just wasted a lot of time.

DocumentationWhen it comes to documentation, you’re pretty limited with existing tools. Very few do a good job of printing points. Heck, Revit doesn’t print them at all (WHY???). I wish that would change of course. If you do a complete interior and exterior scan, why not be able to set a lineweight for the points and print those instead of drawing walls right over them? Of course, even if this worked, items that needed to be demolished or modified would still have to be modeled. Still, who wouldn’t mind cutting their modeling work in half for existing buildings?

As-BuiltsIf your owner is willing an capable (not many yet) then scans are a great as-built tool It provides them with something to give to future teams that is an almost exact match to the installed condition. Given the lifecycle that buildings and their components go through, the cost of scanning is minimal compared to the maintenance, upgrading, remodeling, and future expansions that happen in the spaces we turn over. Owners need better software tools to leverage this kind of data, but sooner than later we’ll be asked to provide quotes for this kind of work too,

You might be making a BIM, but you’re really dumbing down reality.As mentioned above, modeling is really a process of making things less accurate and a little (or a lot) more simple. Keep this in mind always as you’re working with BIMs created from Point Clouds. I cannot count the number of times that people have claimed the model and the scan have identical accuracies. This is simply not possible to achieve even when using the most sophisticated modeling tools. Errors are more or less additive (to be simple), so you should take the total relative error of the scan (let’s say +/- ½”) and then take the error of your modeling process (let’s say you’re also +/- ½” in modeling). If you want to know the total “error” from real world to your model, it is actually +/- 1”.

The reason I point this out is because for many purposes, the BIM objects made from a point cloud are actually less useful than the original point cloud was in the first place. Make sure you’re thinking about this when it comes time to model.

Simplification vs. OversimplificationSimplification isn’t all bad of course. It reduces polygon count which improves performance. It allows you to do things like dimension between two surfaces that were almost parallel in the scan, but can be modeled as parallel in the BIM. The challenge is making sure you don’t cross the line of oversimplification, and the line is pretty hard to define unfortunately. It all comes down to what you’re planning on using the model for of course, but do keep an eye on this one because you’ll only know when you’ve crossed it when something goes wrong!

For an example, imagine a hallway that’s 100 feet long, and imagine that there is a pretty good variability in how straight that wall is in plan – in some cases it is +/- 1” from the average. If I’m

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doing some planning or conceptual design, it is probably OK to draw that as one long straight wall and just get it centered on the points. As we move through to CDs and Construction, that +/- 1” can be a pretty big liability. We should probably break that wall into smaller and smaller portions allowing us to fit each portion more tightly to the adjacent points so that each wall is maybe +/- ¼” or less. If we don’t we could run into some problems from oversimplifying an as-built condition in our BIM.

In Closing…Don’t worry, we aren’t reading this in the class. We’ll be covering some “real world” examples, looking at some of the applications in use, and trying to answer a lot of questions (if you’ll ask them!). This is really supplemental information to the class, or something to reference for more detail than we go over verbally. Most of all, it is a brain dump of 4 years of work using laser scans in the process of delivering designs and constructed buildings to our clients. Laser Scanning is relatively new to our industry, and no one knows everything (much less most) about how scanning should be done in our neck of the woods. But, we’ve got 30+ projects under our belts across our three divisions, plus the work we’re doing for the GSA under their IDIQ contracts to speak from. Hopefully it can help you figure out some of the pitfalls and gotchas before you fall in the pit in the first place.

Happy Scanning,

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Documents

Learning Objectivesaucache.autodesk.com/.../class_handouts/v1_AB5602_Cone.docx · Web viewYou can reduce your daily rate by working with companies that use less current equipment,