How a scanner sees a construction site

Laser Scanning and Reality Capture During Construction

The latest software technologies allow for a full digital construction workflow – design is completed in 3D with building models; complete “mesh” and immersive as-built worlds can be captured; and the possibility to simultaneously combine both in one system to visualise constructed elements versus the modelled intent. Models can even be sent to automated manufacture – rebar machines etc.

Never before has so much data been able to be captured to completely record the building inside and out – allowing for the accurate recording of practically any elements position.

In this paper, we will look at why you might consider reality capture in your construction workflow. Additionally, we will look at the following background issues.

The principle reality capture technologies are:

  • Laser scanning
  • Structured light scanners
  • Photography (applied with photogrammetric techniques)
  • Traditional surveying

Sample current software that this technology can be applied to:

  • CAD and building information modelling packages (Autodesk’s Revit + Autocad; Archicad; Bentley et al)
  • Visualisation tools for proposals and animations (Autodesk Infraworks or 3DSMax say)
  • Clash detection tools (Autodesk Navisworks and others)
  • Meshing; surface and volume analysis tools (Sequoia; CloudCompare; PointFuse; Memento; even gaming engines like Unity)

Storage and delivery of data:

  • Capture techniques generate a large volume of data that needs to be archived – consider cloud storage providers (Azure; Amazon)
  • The same data can also be shared and moved – communication networks or couriering of data can be options – there are also streaming solutions to consider (eg Leica JetStream) which allows small plug-ins installed in the likes of Revit to pull data on demand across standard networks in small chunks.

So why reality capture?

Sample output from a laser scanner .. THIS IS NOT A PHOTO .. but millions of survey accurate, coloured points in 3D space

Sample output from a laser scanner .. THIS IS NOT A PHOTO .. but millions of survey accurate, coloured points in 3D space

Reality capture technologies are an order of magnitude (or five!) faster at “pick up” than traditional surveying.

This is easily highlighted with a few simple numbers – a surveyor using a total station can typically measure in the order of ~ 700 points for a busy day .. a laser scanner by comparison can measure up to 1,000,000 points PER SECOND.

This also demonstrates why the data handling technologies and techniques (your game plan) becomes immediately necessary – there is simply a lot of data inbound.

With this sort of speed available, incredibly detailed areas – like a construction site – can be quickly documented for later analysis.

Aside from speed, reality capture allows for analysis to be undertaken at virtually any point in the captured area. The density of data collected is staggering.

This analysis can be carried out by different professions who might have different needs.

When a surveyor measures an area with a total station (or GPS), they apply their own interpretation of what a client wants – they might measure a pipe at a bend, or measure a wall at either end, or perhaps pick up one point on a column and a radius. But this does not tell the whole story – does the pipe dip in the middle; is there a bow in the wall; is the column plumb?

Analyse a floor for flatness with scan data - points will mm's apart

Analyse a floor for flatness with scan data – points will mm’s apart

Likewise, a surveyor charged with doing an as-constructed survey of a slab say, might measure a point every 3 metres, in contrast, the scanner will return a point on the slab every few millimetres – small ponds and ridges can be made immediately apparent; think of all sorts of questions, chances are reality capture can help – how good (straight and plumb) is a wall; what sort of deformation is there in the water tank; and laser scanning is especially useful for hard to reach things like steel beams or dangerous areas of a site (especially train lines)!

By having millions of survey accurate points available for later analysis (via laser scanning at least), the various professionals can analyse objects in incredible detail – as opposed to the interpretation made by a surveyor delivered in a CAD file.

Software can automate certain tasks as well for rapid analysis – a classic function is clash detection – if you have laser scan data, you can “clash” proposed models against the existing structure to find where the existing infrastructure might interfere with the proposed works – you might want to run a new major air duct for example in a ceiling space – the new design and be “checked” before it is even built and this analysis can happen years after the scan was done.

"Clash" point cloud data against proposed models to make sure things will fit before you make them

“Clash” point cloud data against proposed models to make sure things will fit before you make them

Reality Capture Technologies

Like every industry, reality capture techniques and technologies are ever evolving.

Similarly, of the technologies already available, each one has particular strengths and weaknesses when comparing performance criteria like range, speed and accuracy.

The common categories of equipment are:

  • Laser scanners
  • Structured light scanners
  • Cameras (typically via multi-camera rigs)
  • Traditional survey equipment (total stations, GPS, even tape measures still have a place)

Laser Scanning Overview

The name, laser scanner, pretty much describes it – a laser is mounted on a rotating and revolving “head”. The laser measures distance to a reflected surface and the head measures horizontal and vertical angle. When all these data points are combined – the laser essentially hit something and bounced back at a point in 3-dimensional space relative to the “head” .. the head then rotates a fraction to record the next point .. and the next .. until a “point cloud” is built up. This can happen a million(s) times per second.

The whole unit is then moved – lasers can only see line-of-sight – so to see around corners as it were, the unit needs to be moved to fill in the gaps. Laser scanners can be mounted on tripods (terrestrial), aircraft, cars, hand-held (GeoSLAM) – even backpacks.

The location of the scanner positions can be tracked using targets, GPS etc to combine all the scan data into a seamless coordinate system – map grids, site coordinates, AHD are all options – allowing the scan data to be combined with other data about the site like aerial photography, CAD, models and more.

There are various types of scanners that offer different properties – without getting too technical, some are faster (points per second – eg phase-based lasers), different lasers can reach further (not eye-safe), some are more accurate, some produce less “noise” (time-of-flight lasers – a more stable measurement), some are small (less accurate), some are bulky (more accurate but harder to lug around) .. some have cameras built in. Each job can warrant a different or even multiple choices!

Laser Scanning Summary

Strengths    

Accuracy     Terrestrial survey-grade scanners can achieve accuracies in the order of millimetres when deployed with proper survey techniques (eg control network design or when deployed in combination with total stations).

Range     Depends on the unit, but ranges up to 1.5km are possible – note that range does impact on accuracy (the angular component) (100m+ is typical).

Density    Points are record every few millimetres apart.

Weaknesses

Reflections    Reflective surfaces can do crazy things with lasers. There are mitigation strategies that can be adopted depending on the task at hand (like chalk spray, dealing with bulk reflections with scan clean up).

Speed”    This is a relative measure when considering other reality capture techniques – it does take time to capture an area using terrestrial scanning (incl. photos) in great detail. In contrast, photography might offer a faster pick-up albeit with some accuracy caveats. This “speed” measure also incorporates controlling coordinates of the scanner’s position with targeting etc in the field.

Cost    The scanners start ~ $30,000 and can quickly get to $500,000 (say).

Structured Light Sensors Overview

A DotProduct scanner at a refinery

A DotProduct scanner at a refinery

You probably have one of these in your home and don’t even realise – the Xbox Kinnect Sensor is a “scanner”!

“Banded” sources of infrared light come from multiple sources to create an interfering light pattern. The sensors/cameras can see this and determine angles and distances. By moving the scanning head, the software can “track” the changing patterns of light over the surfaces to maintain a coordinate system.

These are pretty limited though – especially range – they only work over a few metres from the surfaces being measured – but they are great in tight spaces like manholes/chambers or plant rooms.

Google have been looking at adding this to phones via Project Tango. Consider doing as-cons with nothing more than your mobile phone – this gives you an idea of where all this is heading!

Structured Light Sensors Summary

Strengths    

Mobile     These units are handheld and easy to use.

Cost    Under $10,000 gets you in the door easily.

Weaknesses

Range    Only works over a handful of metres – you build up a scanned area by capturing all surfaces contiguously. “Closing” off against previously scanned surfaces allows the software to proportion measurement errors. Targets can be applied to the area for control.

Accuracy    Again a relative measure – compared to a laser scanner, this system is simply not as accurate – but when applied for the right type of “subject” (say a pipe ready to be covered up) it is more than likely accurate enough! It comes down to operator experience and user expectations.

Photogrammetry Overview

This “technique” captures an area with photos .. lots of them. The photos need to overlap significantly – in the order of 80% of each photo needs to overlap with others.

The overlapping photos are then “stitched” together to create point clouds and meshes based on a technique called “ray tracing” – this is all done with specialist software – it does this by matching pixels in corresponding pairs to calculate the relative camera positions and then from the camera positions, determine the locations of pixels in 3D space.

This technique is commonly applied to aerial photography – both full size aircraft and more recently drones. It is great for mines for example – but construction sites work just as well – as does doing things at ground level – think façades.

Photogrammetry Summary

Strengths    

Mobile     Start with a just a GoPro.

Cost    Under $1,000 gets you in the door easily, using Software-as-a-Service processing paid per job (eg Recap Pro).

Speed    You can strap a GoPro to a drone and you are starting to look at how many square kilometres you can map in a day.

Weaknesses

Accuracy    Again a relative measure – compared to a laser scanner, this system is simply not as accurate – you are comparing an engineering grade solution where you are chasing millimetres versus something done well can give you ~ 20 millimetre accuracies. These numbers are actually not dissimilar to the comparison between total station derived data and data gathered through survey-grade GPS – so it can still give you pretty good results!

“Plain-ness”    The software needs differing colours and textures in the photography to be able to generate points. White walls, or very even objects can be troublesome – whereas a laser bounces right off, the photography and software algorithms might not “see” there is something in the area.

Hybrid Systems

We’ll take one with all of the above? Microsoft (yes, them – they also do aerial photography cameras for what it is worth) and Leica both do systems with a variety of sensors.

Microsoft UltraCam Panther mapping backpack. 26 cameras for a total of 172 megapixels, 68 megapixel stitched 360o video, 300,000 points per second multi-beam laser scanner, GNSS, inertial navigation, even a Kinnect Sensors, solid state hard drive array for up to 6 hours of data Probably only a  half-million dollars ..

Microsoft UltraCam Panther mapping backpack ..

26 cameras for a total of 172 megapixels, 68 megapixel stitched 360o video, 300,000 points per second multi-beam laser scanner, GNSS, inertial navigation, even a Kinnect Sensors, solid state hard drive array for up to 6 hours of data and probably only a half-million dollars ..

 

Traditional Techniques Overview

Traditional surveying with total stations and GNSS still very much has a place. Total stations rule when it comes to accuracy .. GNSS rule when it comes to convenience so long as you can see the sky.

These techniques can also offer faster pick-up for isolated objects or very sparsely developed environs – it simply may not be worth getting the “bigger” gear out of the car when you have a tape measure in your pocket for a single distance.

It really does come down to the right tool for the job. Having said that though, sometimes you might not know you even have a job or require a particular distance when in the field, and a laser scanner will probably get it saving you a trip back to the site – eg the client wants to know where the overhead power goes and didn’t ask for it the first time.

Reality Processing Technologies

You have your data .. and lots of it .. now what?

Scanning and photogrammetry have been around a long time – scanning has been available since the ‘80’s .. but it is only recently that the software has really started to catch up. So capturing the data is well understood by surveyors and is far from cutting-edge.

Software you might already use in-house can consume a point cloud from a laser scanner.

Combining the data and the tools is less common in the construction industry, but it is rapidly gaining exposure – it is just simply too good once you start getting into it. There is a learning curve – but it is well worth it! The oil and gas guys especially – refineries and oil rigs etc – have been doing this for decades.

Revit and ArchiCAD can ingest point clouds – so you can simultaneously visualise your model data right alongside existing surveyed points. This gives some pretty powerful and immediate returns.

A couple of Workflows

  • Create model objects from point cloud data – you can see the point cloud, cut sections through it, view it by level and so on – and from there you can drag walls out, model window families say, get level information – this process is typically called Scan-to-BIM. There are some additional plug-ins on the market that can help to make modelling even more productive.
  • Use the scans as as-constructed “Documentation” – the scans can be simply put away until you need them again – it might be tomorrow, could be five years. The scanner can pick up anything that reflects a laser. The documentation aspect is especially appealing for things that get covered up – think slab tensioning cables, under-slab pipes, services in ceiling spaces, rebar in columns. Using open file formats (eg e57 means the files will be accessible for decades) (as opposed to proprietary formats).
  • Model validation – you have already gone to the trouble of modelling your new building for construction, so why not make it match what actually ended up getting built? Your model becomes your as-con. This validation can happen in near real-time – scans can be available within hours – allowing you to check starter bars say prior to the formwork going up for the next pour – scanning allows you to develop a visual survey-vs-model quality assurance workflow. Your model can now live on and be leveraged for facility and asset management (see 6D BIM).
Compare as-built versus intent using heat maps against the original model

Compare as-built versus intent using heat maps against the original model

 

Model-vs-As-built validation prior to further construction .. this is a glass roof designed in Tekla - the steel detail design was compared to what was installed. Construction was analysed prior to the shipment of glass leaving China.

Model-vs-As-built validation prior to further construction .. this is a glass roof designed in Tekla – the steel detail design was compared to what was installed. Construction was analysed prior to the shipment of glass leaving China.

There are literally dozens of software packages available for manipulating point cloud and reality capture data. Similar to the capture equipment, all have their strengths. There are also well attended online forums you can leverage with global reach for when you get stuck or need ideas.

The hardest part is letting go of CAD – you don’t need CAD objects to measure, analyse or visualise your infrastructure – you don’t need a piece of paper – you can even do all of this with a tablet in the field, in full 3D.

Just to revisit – the level of detail possible is simply extraordinary – consider the screenshot below from a newly released meshing tool called Sequoia .. how could this possibly be measured traditionally and be described by CAD? This is a 3D model and not a photograph – it was generated from laser scan data.

Scan-to-Mesh

This is a 3-dimensional mesh .. you can measure from this or view it in Revit!

Storage and Networks

The data is comprehensive, as such there is no escape from there being a lot of it required to describe what you see on screen .. and we are talking gigabytes or terabytes for large areas.

Storing the data is likely going to be outsourced to the likes of one of the big cloud providers where you are paying cents-per-gigabyte-per-month to vault this resource.

Moving the data around is another issue – external hard drives are not an uncommon solution to getting the data from A-to-B.

There are however some newer strategies that could be worth exploring. The latest is a Leica product called JetStream:

  • Scan data is acquired, processed and published to a JetStream server
  • The server can be anywhere – but in the same country reduces latency when using the data
  • A “client” connects to the server and essentially starts requesting screen shots – the server processes the request and sends the “points” back for viewing
  • This way – the file is stored once and can be leveraged by multiple “clients” simultaneously – even shared with consultants
  • This can be done over standard Internet connections – even mobile.
  • “Clients” exist for Autocad, Revit, Navisworks, Infraworks etc
  • The point cloud data could be hosted by the surveyor or the building owner – and consumed by the builder, architect, engineer – the scan data could be maintained as a regular, on-going service – even with daily refreshes say depending on the speed of progress.

Conclusions

Hopefully we have provided some insight into the 3D reality capture world.

There is absolutely no doubt, that as sensors come down in price and size, as storage and networking gets faster and as the software tools get more comprehensive, that reality capture will become as pervasive as CAD is now – the evolution path is clear – paper to CAD .. CAD to reality.

We think the time is upon us where real benefits can come from getting adopting some of the procedures and workflows today .. once the concrete is poured – it is hard to measure something!

We would look forward to exploring this with you further in the future.

 

Download the PDF of the full briefing paper on Reality Capture for Construction.

A point cloud also showing the extracted geometry

Incorporating High Definition Surveying in to traditional workflows

Our client initially approached us to provide a “Detail and Level Survey” of a site in Brisbane consisting of a disused church which is about to be redeveloped for residential use.

The initial scope of the survey was quite comprehensive – the typical detail survey items – plus additional items: windows; doors; roof ridge lines and ground levels; including those of adjoining properties.

You can also view the full report “3D Survey Review” in PDF format.

The survey was to be connected to the Map Grid of Australia and also coordinated with the Australian Height Datum.

A couple of things that have come from our past experience and  talking to this client:

  • we knew that the client was interested in comprehensive 3D spatial data, including that from adjoining properties;
  • previous experience with sharing our point clouds has highlighted that clients and their consultants struggle with these files;
  • total stations and traditional civil drafting packages struggle with true building/architectural 3D.

Given the above, we decided to try deploy a hybrid approach to deliver the highest quality and most appropriate spatial data for all stakeholders.

There were 23 scans performed, mostly at the scanner’s medium resolution. Whilst occupying the stations, the scanner was also instructed to take full 360o panoramic photos.

Total data acquired:

  • ~ 14 gigabytes; made up of
  • ~ 250 million points; and
  • ~ 6,000 photographs.

Below are some screen shots to give some idea as to the data now available. Remember .. these are survey accurate points in 3-dimensional space – they can be measured to .. they are not photographs.

If you would like to know more about this type of workflow for your own projects, be sure to get in touch. Call us on +61 7 3239 5444 or e-mail.

Church Point Cloud Elevation

Church Point Cloud Elevation

Church Point Cloud Building Details

Church Point Cloud Building Details

Church Point Cloud Path Details

Church Point Cloud Path Details

Extracted CAD geometry as a traditional topographic plan

Extracted CAD geometry as a traditional topographic plan

Extracted CAD geometry as a traditional topographic plan + aerial photograph

Extracted CAD geometry as a traditional topographic plan + aerial photograph

If you are interest to know, download the full report: 3D Survey Review in PDF format.

Point cloud interrogation

Point Clouds for Engineers

We noticed an interesting trend in responses to a recent blog post, “The Next Evolution in Surveying .. High Definition” .. quite a number of engineers got in touch with questions about scanning and point clouds. We thought we should do a follow up post specifically addressing some of the queries with a specific focus on how the engineering profession might leverage point cloud data.

In this blog post:

Moore’s Law

.. is the observation that, over the history of computing hardware, the number of transistors in a dense integrated circuit doubles approximately every two years ..

Put simply, computers are getting faster all the time. A similar law exists for storage – although storage density doubles roughly every 18 months!

Why is this important in this discussion of Point Clouds? Because the file sizes are BIG. We wanted to clear that up right away because if you want to get the most out of deploying laser scanners to capture point clouds, you can expect to be sharing some solid files – the downside of having billions of survey measurements at your disposal – not to mention needing workstations with professional grade graphics cards with significant chunks of memory to be able to comfortably visualise the point clouds along side your other data. But bear in mind these workstations are getting cheaper – it is time to get on board with Point Clouds – not to mention, engineering firms tend to have these kind of workstations already lying around!

To mitigate storage and file distribution complications, our Information Technology staff are currently authoring a portal hosted on Microsoft’s Azure datacentre technology to move these things around. Having said that, as Andrew Tanenbaum once said, “never underestimate the bandwidth of a station wagon full of tapes hurtling down the highway”, so in some cases it might be more efficient to courier your data to you on external hard drives!


Quick recap .. What is a point cloud?

 A point cloud is a set of data points in some coordinate system. In a three-dimensional coordinate system, these points are usually defined by XY, and Z coordinates, and often are intended to represent the external surface of an object. Point clouds may be created by 3D scanners. These devices measure a large number of points on an object’s surface, and often output a point cloud as a data file. The point cloud represents the set of points that the device has measured.


How is the data captured?

The laser scanner is set up on a tripod, same as a total station. It is not a whole lot bigger either. Special targets used in high definition surveys are deployed around the site to assist with coordinate control.

We typically deploy a combination of a total station (theodolite) and a laser scanner to a site. The “traditional” total station assists with the survey control – it allows us to get the point cloud accurately on to the same coordinate system / site grid and height datum (AHD say) that you are using with all of your other data: civil, topo, Revit, aerial photography and so on.

This hybrid deployment, which only surveyors will offer, allows for flexible deliverables. Aside from the point cloud, traditional CAD files derived from a total station are a highly efficient way to describe certain types of features at a site – you still need to use the right tool for the right job.

Where a site has survey control, our particular choice of a “survey-grade” laser scanner allows us to mesh the traditional CAD files and laser scan point cloud data with impressive accuracy. Just as quickly, our laser scanner has a dual-axis compensator – same as our total stations (it is a levelling thing). It is also the same laser. This means the measuring specifications of the scanner and the total station are near on-par – these instruments are no toys! But they are pretty cool ..

All of this data can then be aggregated in software like Navisworks and Revit .. more on this later!

What can you expect from a point cloud?

The laser scanner pulses a laser at ~ 50,000 times a second. The laser reflects off surfaces it hits out to about 300m away and the scanner can “see” this reflection. The time-of-flight for each pulse is measured and therefore the distance to the surface is known.

The scanner also rotates through the horizontal axis during the scan, while the scanner head spins through the vertical axis at high speed. This now means we know the direction to the reflected surface relative to all other measurements from that location – each reflective laser pulse has an x,y,z coordinate and also the intensity of the laser return. All of this data is written to the internal solid state hard drive for safe keeping.

When visualised in a graphics package – this database of reflective laser pulses resembles a cloud.

When the scan at the current position is completed, we can also instruct the scanner to take up to 270 high resolution photos. The photos are a further record of the site. The photos can also be used in an additional process back in the office to apply colour to the point cloud – so that the points of the cloud in the graphics software can take on the colour of the surface the laser hit. You can easily alternate the view of the point cloud between true colour, orange (say) – scaled by the laser’s return intensity, black and white or other schemes – one popular one is colours by point elevation or “normals” – based on perpendicular vectors to the surface.

The scanner’s “resolution” (per scan) is configurable – a single scan take from a minute or two, up to a couple of hours – depending on the level of detail required – the maximum resolution of our instrument is described as the distance between points measured on a grid at 100m away from the scanner – a point every 20mm. Because the scanner measures in arcs out from the position of the scanner, the resolution rapidly increases the closer you get to the scanner – so at this resolution at 10m from the scanner you are talking a point every 2mm.

You typically achieve even higher point densities though! When you move the scanner to a new location and scan again, you will have overlap – so a pipe or a column say will be scanned from several locations – meaning more and more measurements covering the surface of the column.

Lasers can only measure line of sight – so by repeatedly moving the scanner you fill in the “shadows”. To get four sides of a column you will need at least two scan stations for example.

This does introduce a complication – all the scans need to be joined up – all put on the same coordinate system. This process is called registration. By registering all the point clouds for a site, you can then visualise the clouds simultaneously – you can then orbit around the column and view it from all sides or interrogate the cloud – for example, determine the size of the column. This is why survey control and proper field methodology is critical – this overlap. If the final derived coordinates for a station or stations are wrong, even by a centimetre, the surfaces will not match perfectly across multiple scans. Conveniently the Leica Cyclone software we have goes some way to mitigate this effect through what is called cloud-to-cloud registration – the software automatically compares millions of points to tighten the overlaps. Notwithstanding – we prefer to see the superb results we get from deploying the total station and scanner together. We typically get better than half-centimetre comparisons between control targets over kilometre ranges.

So when we are talking pricing and deliverables – one of our key products is a Registered Point Cloud – meaning the scanning of the site, all scans subsequently joined together on a coordinate system. Additional variables include level of detail required, survey control and photos for colouring.

Cross section near a column

Cross section near a column – note the fine “line” of points. These points were collected from 5 different scan positions.
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What sort of accuracies are we talking?

You can read all about the accuracies of the relevant scanner – and please ask if you want to know specifics – but simply put, they are pretty bloody good.

Each point in the cloud is good to a few millimetres relevant to the position of the scanner. The position of the scanner in each scan can be coordinated between scans to within a few millimetres. This all means we can easily achieve tolerances requested in typical tenders – 20mm absolute and 10mm relative. We do suggest though for specific tasks – maybe if retrofitting an expensive steel beam say or where tolerances are significantly tighter, we double check any critical measurements with a total station.

When reviewing a “surface” (say a face of a column) – it is usually several millimetres “thick” – meaning the real answer as to where the true surface lies is an average of all of those points. Our software modelling tools take this into account when “growing” or extracting pipes, patches, boxes and other geometric shapes.

It is interesting to compare the point cloud deliverable to the traditional total station pick up.

Taking a simple example – points on a ground/surface grid – the surveyor using a total station might pick up a point on a slab 10 metres apart (say) – deploying the scanner means a point is available every couple of millimetres. Software algorithms can take the huge number of points and offer points on a grid based on options like “lowest point” or “ground point”.

Likewise – consider a concrete beam – our surveyors traditionally would pick points on the beam they think are representative of the shape of the beam, you might get some line work in a CAD file joining half a dozen points describing the beam – now compare this to the same beam defined by literally hundreds of thousands of points captured in a point cloud. Exciting times indeed!


What software can leverage the data?

At their simplest – point clouds are simply a database of points – x,y,z coordinates. This makes the data extremely portable. We can export point clouds in file formats such as plain-old text files, DXF’s, binary/compressed formats and more.

Looking to more proprietary formats, we can distribute files in *.rcp format – as in Autodesk ReCap files. This means files can be loaded in 2014/5 versions of Autodesk Revit, Civil3D, Navisworks and more. This means you can visualise current, as-constructed data, right along side you proposed models.

Navisworks Manage (amongst other packages) can do more advanced things like clash detection. You can load up existing structures capture as a point cloud and compare them to proposed models to ensure the new designs will fit.


What can be modelled out?

Point clouds are great for ad-hoc interrogation, visualisation and animation and clash detection workflows. Invariably though, users will want CAD style outputs derived form the point cloud.

We can create models and line work from the point cloud using specialised software. It does take time to do – you can liken the software to the early days of OCR (optical character recognition). As the software matures, more and more automated feature extraction functionality is added. We can currently extract things like: pipes; surfaces (patches); steel work (like “I” beams) based on library models; meshes; and ground points-on-grids and contours – but it is a fairly labour intensive process.

These features can then be moved around as Autodesk faces and solids for example, or imported into Revit as masses.

Revit is a little trickier – it likes things to be perfect – floors to be perfectly flat, walls to be vertical or right-angled, columns all to be precisely square and same uniform size. Buildings are never built perfectly – and the point cloud shows it up! That is not to say you can’t model in Revit – but we will have a discussion with clients based on the level of detail (LOD) required. For example – does Revit need to know a wall is built at 87.2 degrees vertical, or can the wall be approximated in Revit. For a building information model (BIM) – this is probably all that is required – but if you wanted to retrofit an expensive steel beam – you would refer back to the original point cloud for more precise data about the features.

A pipe modelled from points

A pipe modelled from points
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Beginnings of a model

Beginnings of a model
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Hopefully the foregoing has been of assistance. If you would like to know more, perhaps even grab some sample point clouds off us, don’t hesitate to give us call – +61 7 3239 5444 or e-mail us.
Regatta Hotel point cloud

The Next Evolution in Surveying .. High Definition

 

We have recently invested significant resources to be able to deliver high definition scanning deliverables to clients. Be sure to discuss how point cloud data could fit in with our existing work or be used to document your site.

A point cloud is a set of data points in some coordinate system. In a three-dimensional coordinate system, these points are usually defined by X, Y, and Z coordinates, and often are intended to represent the external surface of an object. We can now create point clouds by deploying a 3D scanner. These devices measure a large number of points on an object’s surface, and often output a point cloud as a data file. The point cloud represents the set of points that the device has measured.

When Cyril Bennett started this practice in 1917, we doubt he would ever have envisaged the technological advancements witnessed by our firm over our subsequent 97 years.

Surveying and its related disciplines of navigation, geodesy and cartography, have always been at the forefront of technology.

Surveyors have always strived for improving accuracies – it is in our DNA – from the time of the first map of the World in ~ 600BC, the construction set out techniques of the Egyptian pyramid builders, the cartographers and explorers like James Cook – we are even now collecting data and making maps of planets with multiple missions surveying Mars!

Perhaps arguably the biggest single contributor to the increase in accuracy on our ability to measure is the invention of the laser in the late 1950’s. Armed with a laser and the known constant of the speed of light and an accurate clock, we could now measure over much greater distances than with the old steel band!

This one step improved accuracies by a couple of orders of magnitude from ~ 1cm per 100m to less than 3mm over 1km. Metrology lasers can even measure with accuracies in the microns (1/1000th of a mm)  over short distances (<50m).

Total stations which have been around for about 30 years, combine sensitive angular measurements (say 1 second of arc – or about 0.02% of 360 degrees around) and distance measurements in a single device – and these are what your typical Surveyor now uses to “navigate” and measure things like the cadastre (lots of land) and to set out marks for construction.

Total stations went “robotic” about 15 years ago – in other words they had motors added to control the direction they were looking – and this now allowed remote operation.

Speed and size of data storage is the final part of our story – we can now collect gigabytes of data quickly and easily.

This has all lead to the aggregation of a these technologies into a laser-based point cloud scanner – and more to the point – a technology we can now deploy to assist with your projects.

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Our terrestrial laser scanner can collect a staggering amount of information in short time.

Our scanner is capable of collecting 50,000 survey-grade, 3-dimensional measurements PER SECOND – resulting in a database of a “cloud” of points surrounding the location of the scanner – measured out to the range of the scanner which is about 300m.

By moving the scanner repeatedly, we can collect even more data about the environment the scanner is deployed in.

The scanner also takes 270 high resolution photos of the location per set up – which are stitched together to provide a 360 degree panorama – the photo data is also used to provide colour data for the points, supplementing the intensity data from the laser’s return – resulting in a new photograph like record of the scene – but in 3 dimensions.

And it is fast – in a day we typically collect in the order of 200,000,000 survey points! Yes – 200 million measurements with millimetre accuracy. Combined with our other technology – total stations – we can have billions of points of your site on your site “grid” or coordinate system – allowing users to measure between practically anywhere the laser can get to.

This technology is now used for recording data about:

  • heritage buildings;
  • crime scenes;
  • vehicle traffic accidents;
  • metrology (like measuring an aircraft wing);
  • as-constructed data (like pipes, columns);
  • building information modelling;
  • mine stockpiles;
  • and many, many more applications.


Video: animated fly-through from a ~ 42 million point cloud.

Modelling features from a point cloud to CAD

Modelling features from a point cloud to CAD