3 Myths About Laser Scanning and Point Clouds for Architecture and the Built Environment


Warped curtain

Are laser scanners and their resulting pointclouds right for you and your project?  As with all lists, it is simplified and of my opinion.  Whether you want to trust my opinion, well that’s up to you, but my company Interioreview has, for over a decade, surveyed / drafted / modeled hundreds of buildings and starting in 2006 delivered Revit Models of existing buildings.  My company, PointKnown, has created an Add-In to Revit that allows you capture and model  buildings as you measure, in real time with a hand held laser.   Now that I’ve blown my own horn here are my top 3 Myths:

It’s Foolproof and Error Free.

Wrong.  I have not once received a model from a ‘pointcloud’ surveyor without dimensional errors in the model.  Not once.  Only because of our internal controls and surveying was I able to call out the errors and was not satisfied with other companies internal controls that the errors would have been found if my company had not found them.  Such that we now will do all the modeling in house.  Just because someone has a scanner does not mean they do it well.

From the “Analysis of The Accuracy of Terrestrial Laser Scanning Measurements” FIG (International Federation of Surveyors) Paper

it is concluded that features such as reflectivity, color, and brightness of the  object surfaces have impact on the quality of the data, therefore, although 3D point cloud data is very useful it should be considered that the data can be sometimes irregular and corrupted and thus not exactly reflecting the features of the scanned object.

It’s Easy to Produce a Model From a Pointcloud.

Holy cow, no.  How many technologies come into play to get a scan created, consolidated, registered, exported, modeled? First the hardware/scanner, whether it’s from Leica, Faro, whoever, they have their own software to manage the scan/cloud, and then you can export/import to Revit to use as a background to model over.  You can use other technologies to help with this process such as Scan to BIM, or to cut portions of the pointcloud you can use ReCap, export to Autocad and re-import that data into Revit, etc.  My point being there are a variety of methods to get from here to there but they are not necessarily consistent and have their strength and weaknesses, but you are using human power to make those decisions at each step.  And then you are essentially using the pointcloud to ‘trace’ over.  That is, you cut sections of the pointcloud in what ever view you are working in and trace over them.  Has the person ‘modeling’ the building ever surveyed a building?  Or have construction or architecture experience to know how a building should be put together.  Does the architect really want to see a wall with a .08 degree deflection of wall off 90 degrees because it will create numerous amount of Revit errors, and was it really there or was the pointcloud interpreted incorrectly?  There is no easy button.

It’s Cost Effective

Putting a scanning crew on site for a day is going to cost you between $3K-$4K typically, just to get the exterior of a building, with the pointcloud only, expect at least a 2 day buy in for between $6K and $8K, and that’s typically without going inside, and at the end you get the point cloud, not a Revit model. So a typical house, modeled from a point cloud, inside and out, best guess $8K-$10K.  12 Story Commercial Office Building, $50K+ and so on.  Maybe that’s in your budget, but if so why?  Why would you need to spend thousands of dollars to be told a room is square and has a 10′ ceiling?

Once dealing with the pointcloud, if you are dealing with it yourself, I hope you have a box/computer that is going to have a minimum of 16GB RAM, multicore XEON processor, etc. and ideally has a solid state drive, this is recommended by Autodesk for ‘pointcloud’  interactions.

You as a consumer of this data need to know what technologies are out there, your choices and their cost.  I have seen circumstances and white papers where laser scanning pays dividends many times over, most consistently in existing exposed MEP intensive facilities, think utilities, drilling platforms, power-plants and the like where having a accurate representation of all that data can allow people to retrofit power-plants with few change orders or zero defects.  Imagine an offshore construction platform that can lease for $100’s of thousands a day finishing early because of the accuracy of data, very good investment indeed even if it costs $200K to model it accurately.   However, do you need that kind of data for a commercial building or an adaptive reuse project?  How are you going to capture the interiors?  There are methods to capture the built environment accurately for your needs without wasting money and effort.

Conclusion

Start with the simplest model you need, dimensionally accurate, volumetrically correct using whatever technology that gets you there cost effectively and with a level of confidence.   Adding details to the model should be done dependent on scope and need.  Power-plant of a building, you may want to bring in a scanner to model the piping package, etc.  Accuracy of a historic structure that you may need to impact because of a project, sure scan it, but to scan an entire project is overkill in many circumstances no matter what you are told.  Scan where you need details added.  Know your options.  Your tool box needs more than a hammer.

 

 

Share

, , , , , , ,

  1. #1 by Tim on September 18, 2013 - 1:30 pm

    Hi there! I had a few questions about the data you’re referring to in this article. I do quickly have to say though that this is a great piece, well and fairly written. I’m excited, as a huge proponent and user of BIM software, to have found this blog via this article.

    First of all I do have to say that it is certainly true laser scanning is just beginning to become a BIM-friendly enterprise. Until just recently the workflow to produce such models was frankly too costly. I personally would look on the technology with a little more optimism; from the Beta’s Autodesk has released and more innovative programs such as PointCab are taming massive pointclouds to easily processed entities. I’m looking forward to seeing a vastly improved workflow as far as software goes; where BIM is concerned it certainly leaves something to be desired.

    While I could not agree more that just because someone has a scanner doesn’t mean they use it well, I do have to say that those properly equipped with right accessories / control points such as reference spheres do produce highly accurate and consistent scans. Typically scanners are used in more industrial or GIS related jobs, but technology like registration spheres makes detail scans a more feasible task.

  2. #2 by Kristen Sandoval on October 3, 2013 - 2:23 am

    Its a normal myth that it is easy to produce model from a point cloud. But, People are still trying to work on this.

  3. #3 by Jim Foster on October 11, 2013 - 9:46 am

    Tim,

    Thanks for your post. Please let me know what questions you have and I’ll do my best to answer them.

    best,
    Jim

  4. #4 by Nayeem on November 6, 2013 - 10:54 am

    Hi Jim,

    Great article, this is spot on! My work is just coming to grips with the daunting task of trying to export our laser scan point cloud data to Archicad, which at the beginning we thought would be a walk in the park. Only now have we realised how difficult the process is.

    I was wondering if I could pick your brain as it is quite obvious you have a lot of knowledge in this field. Our firm is trying to find a method of bringing our point cloud data into our modelling software (archicad) without the processing software squaring up the walls and floors. We work entirely in old renovations and need to model existing conditions including sagging floors, slanted and crooked walls. Would you happen to know of any software that can detect planes along points and export them without making them ‘perfect world’?

    Any pointers would be greatly appreciated!

    Nayeem

  5. #5 by Jim Foster on November 13, 2013 - 11:28 am

    Nayeem,

    Unfortunately I have very little experience with Archicad and am not familiar with the tools to utilize / integrate pointcloud data.
    I typically start with a basic 3D/BIM Model, volumetrically correct and then add detail as needed utilizing what I think is the appropriate technology.
    So we may build out a building with PKNail Pro directly into revit and then have a limited number of scans to capture details that are needed, so instead of
    trying to deal with a huge pointcloud, clipping it, and extracting details and the cost to scan etc. have a defined limited scope for the scan data.
    I have done many historical buildings, and when I deliver, typically the architects do not want to see things out of ortho or plumb as it creates a massive amount of headaches
    to deal with from the design perspective. So they would rather have a model be 98% correct, than 100% showing everything. Like any project an honest and clear discussion of the scope and deliverables at the outset will drive our projects and what we deliver.

    Sorry I could not be more help with the plug ins. Good luck and if I can be of any help please don’t hesitate to contact me.

    best,
    Jim

(will not be published)