3d Laser Scanning to CAD.

December 7, 2016

Laser scanning has grown tenfold in the last few years and for us is now the quickest and most accurate way of capturing existing geometry. I've put together this article to highlight its benefits, applications and limitations.

 

Laser Scanning is a joint process of lasers (invisible) and camera's. The laser(s) are sent out and terminate upon impact with an object, this termination creates a point (cloud) in virtual space. This process is done by the millions and in a full 360° cycle per scan. 

The scan data is only what can be seen in line of sight so to capture the reverse side the scanner needs to be moved until all required angles/surfaces have been captured.

 

The HDR process is unaffected by light and can even work in pitch black circumstances.

White light laser scanners for example the FARO freestyle hand-held will not work well in sunlight so please be careful if/when choosing a scanner.

 

People and moving objects in and around the scene being scanned aren't really an issue anything that crosses its path will be merely noisy data that can be deleted but obviously anyone restricting the line of sight for a long enough period will show up in the scan cloud.

 

The FARO HDR (among others) use a class 1 laser which is safe for human exposure.

 

The Scanner.

We typically use a FARO HDR 330 for large scale scanning with it's 0.1 - 330M range it is awesome for most applications and offers good accuracy at times 1-2 mm is achievable depending on the circumstances.  

 

Scanning times can take anywhere from a few minutes or up to an hour depending on the quality and point density required. 

For reverse engineering or wear analysis a few minute scans is more than enough and keeping the point cloud file size for your CAD suite is key.

 

The scanner can be used on it's tripod either right way up, upside down or removed from tripod and placed on the floor. Ideally each scan should be taken within the recommended +/-5° from vertical, however scans can be easily aligned in ReCap if this is not possible.

 

Accuracy

This is where it gets confusing... Put simply the scanners are as accurate as they need to be the problem is the human ability to select the dots in space. The point cloud data is very messy and scattered especially when zoomed in. Therefore when modelling over point cloud the accuracy is only as good as the ability to select the correct reference point(s) in space. Though 2-4mm is easily achievable and anything requiring more accuracy we will supplement the scan with hand measurements.

 

 

 

 

There is software that features "wrap/drape" techniques using the point data as references and essentially draping a surface over the geometry, this in theory is most accurate, but is often too good and will give you a wrinkled surface to deal with. 

 

 

 

 

 

 

 

 

For greater accuracies there are CMM options either touch probe or arm mounted high accuracy scanners which are often used in a machining environment where sub 1mm is critical.

 

 

 

 

 

 

 

Processing Software such as Autodesk's ReCap 360 is used to read, align and modify raw scan data ultimately producing the point cloud which can then be exported into your CAD suite  or "real view player" of choice.

 

The processing software is really easy and quick to use. It can handle massive scan files without any real issues and if there is good scan overlap the automatic registration is usually all you need to align your scans. If you have scans that were in a difficult location or don't have any external geometry that features in the previous scans a manual registration may need to be done. This is a series of selecting common datum's in one scan against another until the software has worked out where the scanner was in relation to the other scans. 

As a rule more time spent scanning is usually less time processing..

 

Once scans are registered the software moves to an editing environment that allows you to delete point data that isn't relevant to your task, divide data into segments or simply take measurements. From here the registered scan file can then be exported to .e57, .PTS and other common point cloud formats.

 

Post Processing is where the point cloud is imported to a CAD suite and modelled over. 

Most reputable 3d CAD packages will offer the ability to import scan data.

 

Wear Analysis can be achieved with laser scanning, helping you to pinpoint high impact and wear zones in chutes or abrasive piping environments.

This is useful for forecasting maintenance reducing unnecessary exchange of wear liners.

 

 

Rubix Design can assist with all things scanning related. Alternatively Position Partners rent laser scanners for a great day rate if you would like to play for yourself. 

 

Get in contact today to discuss your next scanning or CAD project.

 

Rubix Design 1300 00 337 446              Position Partners 1300 867 266

 

Info@rubixdesign.com.au                       Ben: BStieger@positionpartners.com.au

 

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