PointSCAN 3D laser scanning Heritage Survey

A GUIDE TO 3D LASER SCANNING

This is a short guide to explain some of the terminology, techniques and processes used in 3D scanning to help let you decide how you can gain the most benefit.

As 3D Laser scanning is becoming more and more integrated within today’s hi-tech delivery processes it should be realised that it is not a new invention, in fact it was first introduced in the 1960’s, although it is safe to say that they would not have been as portable as they are today.  

It has only really been since the turn of the century that technology has given us the capacity to use and store such large data files effectively and whilst the technology has become more economically cost effective to manufacturer it is more accessible and commercially viable option for design and project management.

Over the years I have been involved in many major engineering and construction projects. When I was introduced to 3D technology I saw it for much more than a design tool, but as a way to unite a project team in a way that they to could visualise the project. 

3D LASER SCANNING GUIDE

Reality Capture

Before I start it should be noted that 3D Laser scanning is not to be confused with other forms of 3D Scanning which again having been around for over a century but have become more and more popular over the past few years.  Both processes will produce a digital model however the initial capture of the information is completely different and where relevant I have made comparisons between the two because 3D laser scanning may not be the right solution for your project.

3D Laser Scanning or Lidar

This process relies upon the scanner to transmit a laser beam until it hits an object at which point the light is reflected back to and captured by the scanner.  The light returns at a slightly different wavelength and it is this variation that can be measured.  Because light travels at a constant speed the variation can be calculated as a distance therefore producing an accurate point in space. Scanners repeat this process up to a million times a second leaving behind a 3D image made up of millions of dots otherwise referred to as a point cloud.

PointSCAN Lidar explained

3D laser survey offers a safe, fast and accurate solution to obtaining on-site measurement data which is supported by three-dimensional imagery making it ideal for design and project management applications.

Photogrammetry

Converts photographs taken from a standard camera, or number of cameras stitching them together using computer software to form a digital 3D solid.  This is commonly used in UAV’s and drones but is particularly good at capturing instant images where an object is likely to move.

Metrology

Most portable laser scanners have an accuracy of 1-2mm and photogrammetry equipment dependent upon the application even more and would not necessarily be suitable for measuring below this.  This is an area known as metrology and uses either a probe or laser scanning equipment to acquire data to microns and is widely used in precision engineering, aviation etc. 

Geomatics

This is the scientific / technical term used to encompass how geographic data is acquired, stored, documented and presented or visualised.  Whilst 3D Laser Scanning clearly falls within this category it also encapsulates all other data gathering techniques and would also be included as land surveying and geodesy.

3D LASER SCANNING GUIDE

What type of 3D survey do you require?

Well as with most applications it is dependent upon the final outcome and what you would like to use the information for.  Once processed all forms will produce a digital 3D model which can be delivered in similar formats.  Personally, I have found Lidar an excellent way to measure larger objects, sites, buildings and structures where the measurement data is the key deliverable.  This works particularly well, but is not confined to, an engineering or construction type application.  The visual element then allows for this measurement data to be viewed and can lead to significant savings against time and cost when delivering a project.   

 Photogrammetry on the other hand is very good at capturing instant images, this is why it is the preferred medium for capturing people as there is less chance of the scan data being obscured due to movement.  These processes are commonly captured on camera rigs using multiple cameras to record data at the same time or by using fewer cameras and having an object rotate while the cameras take multiple shots.

 

UAV's or Drones

 

In the past few years it has also become the new go to application for UAV’s or drones to be used to survey sites or open areas where they can collect a large amount of data at a time.  These are mostly camera-based systems although Lidar has been successfully introduced, but at the present time the weight does create limitations not to mention insurance!  Remember that there may be restrictions on flying around your intended area and you should always seek the guidance of a qualified CAA pilot.  Another good point is that ground based scanning can often produce more accurate measurement data and detail as they are closer to the source and can also be viewed from an aerial prospective.

Regardless of the source of acquiring the data, it is important that you capture as much data as you possibly can from your survey.  I am often suggesting to clients to make the most of our time on site.  The wonderful thing is that a 3D laser scanner will capture data around 360 degrees and whilst some scanners will reach 1km most can operate up to 350m with very good results.  Clients would often ask for a specific object or area to be scanned and it is often more cost effective to look at the bigger picture and survey more than you need. 

3D LASER SCANNING GUIDE

Registration Process

So, with the survey now complete the data needs to be processed.  All the individual scan need to be aligned and fitted together. Modern 3D scanners have the capability to do this as they scan but I still like to go over the registration data to check alignments and tolerances.  The registration process is basically like putting together a digital 3D jigsaw puzzle overlapping scan data and joining like for like scan points.  As more and more scans are registered together it builds up a image in 3D made up of millions of dots or points. Surprisingly this mass of dots is called a point cloud.  

When individual scans are processed together the registration software looks for the best fit between each overlapping scan point. Once the scans are all registered the combined deviations between all the registered scan is totalled up to provide an overall survey accuracy.   PointSCAN would look to achieve a registration tolerance of under 2mm for a completed survey.

When attending a site, and dependent upon the size and duration of the project targets and spheres are often set out to assist in the registration of the scans.  Software improvements will register scan data without them, but their use does aide the registration process.  It is also good practice on larger sites to set up a series of control targets that different scan areas will relate back to.

 

Geo-referencing

3D laser scanners have built in sensors, inclinometers, dual access compensators, compasses and GPS to assist alignment.  However, the built in GPS accuracy is often limited, using similar technology to the apps on a smart phone. Therefore if known survey points are acquired within the scan data exact GPS co-ordinates can be allocated to that position. This then  aligns the rest of the point cloud, an excellent feature for topographical surveys allowing the scan data to align with the site datum’s and elevation which can then be noted on the documentation.

Scale?

Your original scan data will be captured at 1:1 scale allowing measurement to be obtained without scaling. 

3D AutoCAD model
3D AutoCAD model

3D LASER SCANNING GUIDE

What can I do with the 3D scan data?

At some point you are going to want to present your scan data in one format or another. Once the final point cloud has been stored digitally compatibility can be found with most major software applications with common output formats being a 3D CAD model such as AutoCAD, Revit, Solidworks to name just a few.  From this you can create 2D printed version for plans or fabrication drawings.

You may have heard of terminology such as ScantoRevit, Scan2BIM, ScantoCAD or various other hashtags but these are only references that the scan data can be converted to support a particular software.

Another output option is to utilise the point cloud, you already have an accurate 3D representation so you may ask why you have to model this again if the purpose of your design doesn’t require a large amount of surrounding detail.  3D models can be imported, overlaying them against the point cloud, this can save time and is a cost-effective way of identifying clash detection without having to model the whole site.

Many software applications allow you to mesh the scanned data.  This is a process that converts the point cloud into a digital solid object by triangulating points to form a surface. Meshes can then be processed as a 3D solid instead of a point cloud and again have multiple uses in 3D CAD software.

Physical modelling – Once you have converted the point cloud into a solid the file can be outputted to a 3D printer however its always a good job to check your scaling!

As-Built Documentation

In the same way a survey is completed to prepare and design a project 3D laser scanning can be used to verify a project.  Unless specific to a project most designers will attempt to design with straight lines. Walls, windows and doors will have 90-degree angles, it’s how computers work, but in reality the final project deliverable may have some discrepancies.  These may have been deliberate changes taken as part of a design change or even an oversight, but it is important that they are recorded.  A 3d laser survey offers a fast and simple opportunity to capture the as built environment and overlay it upon the original 3D model making any discrepancies easily visible, especially useful in handover documentation and BIM modelling.

BIM (Building Information Modelling)

Information and documented details of a building structure and services that are required from the initial design, construction through to occupation and management.  A digital blueprint that allows all parties to easily and accurately identify specific items within the make-up of a building.

PDMS

Another useful acronym Plant Design Management System is software linked to 3D CAD that allows for each individual part to be documented via a database.  This allows future users to view specifications, tolerances and capacities from within the 3D modelling system.

Digital Transformation

This is a process by which your registered scan data can be modelled and viewed in different visual formats.  Whether it be an augmented presentation popping out from a page or a fully immersive virtual reality environment.   There are many ways of viewing this type of virtual reality, through smart devices, headsets and Hololens through to transforming a room into an 3D immersive cave. So, what started as some simple measurement data has the ability to drive innovation and creates engagement throughout your project delivery team.

BIM Survey
3D Point Cloud

3D LASER SCANNING GUIDE

What Level of Detail can you expect from a 3D laser survey?

When you capture the scan data you are basically recording an exact representation of that moment in time and once you have the data you need to choose how much of it is relevant because too much data can be as inconvenient as too little. You must always remember that the original scan data can always be referred back to, so when it comes to modelling it is sometimes better to leave out information that may not necessarily be required. (Yes less is sometimes better).

It is for this reason that PointSCAN use a level of detail scale that firstly clearly defines what the final outcome will consist of.  As a client there is nothing more frustrating expecting a Ferrari and getting a Morris Minor and the same exists with our Documentation

Levels of detail can however be used in combination, for instance you may have some items in a room that needs a high level of detail but you also want to show the room but just need to know its there rather than detailing it.  This will allow you to manage file data sizes and prevent processing issues when importing into 3rd party applications.

 

standard levels od 3D modelling detail
Levels of 3D modelling detail

LOD1

LOD2

LOD3

LOD4

3D LASER SCANNING GUIDE

How long does a 3D laser survey take?

An individual scan usually takes between 1.5 to 7 minutes. Typically PointSCAN will aim for between 64 and 150 scans in a day but it is all dependent upon the quality, and colour options.

Photogrammetry can be captured instantly but may require more photographs to capture sufficient information, but of course, it does all depend upon the items being scanned.

Please also allow enough time to set up the equipment.  It is also important to note that there will be some post survey processing.

This is also true when it comes to the documentation and this is really where money can be saved or indeed wasted.  I would very much like to model everything to the finest detail because I want to demonstrate how good 3D laser scanning is however the general rule is the more detail you require the longer it takes to model and the larger the file size is to work with and ultimately he more it costs.

 

3D LASER SCANNING GUIDE

How much does 3D laser scanning cost?

Everything comes at a cost and the decision is ultimately that of the client as to whether they can justify these costs against their project.

PointSCAN categorise their costs against
Acquisition
– the physical scanning to the conclusion of a point cloud,
Documentation
which is the output files and
Digital Transformation
which enhances and animates the documentation.

Of course there is the physical cost of attend site, but also remember there would have been a cost to complete a traditional survey any way.  Prices vary between suppliers and applications, but I would expect a days (up to 8 hours) scanning to cost between £550 – £1000. 

Documentation is of course based upon the quantity and level of detail of the final output files and is a variable based upon time taken to produce. I would expect the cost increase to be at least 70% more for each level LOD1=£100 therefore LOD2=£170 and LOD3 =£279 AND LOD4 =£491.  

Digital transformation as with documentation would be aligned to timing and staff costs.

However, there are also some hidden benefits that can improve projects costs.

What is not always calculated is the savings this technology can achieve.  Good quality data is an essential element of any design and can lead to a faster design process as fewer changes need to be made, better designs equate to better delivery all of which reduce programmes saving time and money.  So, the enhanced cost of scanning could lead to significant savings across the course of a project.

Its an old adage but you do get what you pay for and if it seems too cheap then look for the catch.  I’ve seen scans advertised from as little as £40 per scan but be aware of a minimum amount or in that case a 100 scans in a day can be very expensive. Also make sure you are getting the registration of a point cloud as a minimum for the final output as software to convert the raw scan data can be expensive.

Scanners are available to hire, which is another way to minimise the cost but unless you have experience and a good knowledge of the software the final result may not be as expected. Also remember that by the time you have hired the equipment and gone to site and completed a survey many scanning companies will offer a comparable price.  More importantly if PointSCAN were to miss some data then a second site visit would be at our cost.

3D LASER SCANNING GUIDE

What can be scanned?

Just about anything. I often look at building architecture, mechanical plant or historic structures and say “I’d love to scan that,” just because it would look good.

Realistically though there is no point, (pardon the pun), if there isn’t a valid use for the information.  

There is also, as explained above, a cost to complete, it may not be cost effective to scan a room for a plumber to install a new tap as it is fair to say most domestic properties do not require this level of digital design and record keeping, however the future is already seeing, faster, cheaper technology being introduced.

3D LASER SCANNING GUIDE

Are there limitations to 3D Scanning?

3D scanning is only as good as the person positioning the scanner and the operator must have an amount of special awareness.  It is not always as simple as pressing a button and moving onto the next position in a random fashion, although it may look like this at times.  Unfortunately, they do have their limitation for example both lidar and photogrammetry will only capture line of sight and we are yet to see x-ray vision to record the surface below.  As mentioned earlier Lidar is not really suitable for anything that could potentially move, a person for example would require a number of scan positions for which it would be extremely hard to hold that position for the required amount of time however photogrammetry would not be my preferred option for a measured building survey.

Both options can be affected by inclement weather.  Not only because nobody likes to stand in the rain, both formats can be affected by water droplets obscuring the lenses, in the case of a laser scanner raindrops can act as a prism deflecting the laser instead of bouncing the beam straight back to the scanner. The same affect relates to any body of water which translates onto scan data as shadows or voids.  In both cases software may compensate for this but it may affect and accurate registration.  

Cameras are improving but photogrammetry does however require a suitable light source and cannot therefore work in total darkness; it may also be affected by bright light. 

Unlike a camera that needs light to register the image through the aperture a 3D laser scanner generates its own light making it ideal for these applications. 3D scanners have the capability to capture colour and combine this with the scan data producing excellent 3D colour point clouds but another tip to remember is that the capturing of colour imagery extends the scan period limiting the maximum amount of scan. As with a camera the colour imagery is subject to glare from bright light source and many CAD operators will switch off the colour during registration as the planar view produces a clearer image.

Camara image of roof space
Camera image
3D laser scanner generates it own light source for BIM Survey
Lidar image

3D LASER SCANNING GUIDE

Is Laser Scanning Safe?

Yes, it is, in so much that both lidar and photogrammetry are non-intrusive and do not need to touch anything they are capturing.  

Objects can be scanned from a distance or by remote operation. This reduces the risks of entries into hazardous areas such as confined spaces. It can also prevent working from heights and the requirement for additional access equipment.  

In fact, Virtual Reality allows an entire project team to have access to a hazardous area from the safety of their own office.  So there is no need for any additional safety training or equipment.   

Whilst older class 3 laser scanners required eye protection for anyone in the area modern class 1 scanner equipment will not cause any eye damage.

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