Corgarff Castle and Elgin Cathedral

It’s been almost 2 weeks since my fieldwork trip to the Highlands – a 4-day survey whirlwind through several locations in the North of Scotland, including Inverness, Elgin, Fortrose and Corgarff. Most of my time was spent laser scanning Corgarff Castle – together with HES colleagues from the Fort George office and Li Sou from Historic England. Corgarff is a very special site: a striking white garrison tower surrounded by star-shaped walls, located at the edge of Cairngorms National Park. The location is very remote, but the views were stunning.

One of the highlights of the trip was certainly my return to Elgin Cathedral. Elgin was my first field project with the Digital Documentation team and provided the material for my very first post on this blog (see Elgin Cathedral QTVR). The objective was to photograph the interiors of the two towers of the Cathedral in order to produce a new set of QTVR panoramas – documenting the spaces after the installation of the new interpretation suite. We used the same set-up as before (Nikon D810 mounted on survey tripod using nodal ninja) with a few improvements (HDR photography using 5 brackets instead of 3, plus remote shutter release to eliminate movement). The system worked really well and we managed to finish the job in a few hours with great results. The only (slight) downside of this process: 5 brackets for every angle (3 rotations plus ceiling shots) resulted in approx. 150 images for each location (in RAW and JPG) = a lot of storage space. However, the quality of the final panoramas definitely justifies the file sizes!

I have already processed the raw photos in Photomatix to create the HDR images, which I’m now stitching together in PTGui to produce the panoramas. I’ve been using only RAW photographs for processing and exporting uncompressed TIFs, which doesn’t seem to add much to processing time, but really makes a difference to the quality of the final product.

My visit to Elgin was a great chance to finally see the stone collection properly displayed in the brand new exhibition, after a year of conservation work – which took place literally next door to our office in Edinburgh, in the HES Conservation Centre. The dark purple display stands were a perfect choice for showcasing the stones. The effigy of the bishop is one of the highlights of the collection – the light projection system used to display the colour scheme onto the stone is brilliant.

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Colour scheme projected onto the stone effigy.

Once the QTVRs are completed, my next project will be to process all the laser scan data from Corgarff Castle and Fortrose Cathedral. I’ve already imported all the data into Cyclone using the Auto-Align function, with moderate success (it gets confused by repeating geometry such as staircases with sometimes “interesting” results). However, auto-align can be a great tool for quickly checking results at the end of each day on the field – when there is still a chance to go back and fill in any gaps.

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Laser scanning Kinneil House

A few months ago, the Digital Documentation team spent 2 days in the Kinneil Estate near Bo’ness. There were several reasons for this visit; one of them was to collect data (laser scanning and GNSS) in the area of the Roman fortlet for a PhD research project on the Antonine Wall.

The other reason for the visit was to laser scan Kinneil House itself for the Rae Project, our programme of digitally documenting all of HES’s properties in care. I was sadly not involved in scanning the House, which has some incredible Renaissance wall paintings and really is worth a visit. I was, however, given the task of processing the data, registering the scans in Cyclone and producing the deliverables: TruViews and a set of orthoimages (plans, elevations and sections).

The project consisted of P40 scans with HDR imaging for the exterior, plus HDS6100 and Faro scans for the interiors (total around 60 scans). I registered the scans and then cleaned them in Cyclone to isolate the building, remove trees, people and occasional noise from the data. For the orthoimages, I experimented with different visual styles, to see which one would bring out more detail in the point cloud. In the end, for each view I exported the same ortho-TIFF with different visual styles (shaded and silhouette) and combined them in Photoshop. Here are some of the results:

The Hidden Landscape of a Roman Frontier is joint PhD programme between HES and Canterbury University. For more info see here or follow Nick Hannon @Hannon_Arch on Twitter.

The local charity group Friends of Kinneil have been very enthusiastic about our work on the site. You can follow their activities on Twitter @kinneil.

And, as always, follow Rae Project activity on Twitter #RaeProject.

A trip to York, and Lancashire, and London…

It has taken me a while to post this, but the last month has been really busy. So, recap of the past 3 weeks:

Week 1, a trip to York (and Lancashire, and London) on an intern exchange programme, hosted by Historic England’s Geospatial Imaging team. Li (who has already blogged about this -check out her blog here) is the Geospatial team’s CIfA placement and will be joining us this following week in Edinburgh (and Inverness, and Fortrose, and Elgin) for the second half of our exchange.

My week with Historic England was busy, packed with site visits (amazing Rievaulx Abbey and Mount Grace Priory), an SfM photogrammetry session at English Heritage’s archaeology store in Helmsley, a laser scanning survey of Bellmanpark lime kilns in Clitheroe, and finally a day trip to the Natural History Museum in London. I had the chance to participate in field work as part of the team, both in Helmsley (photographing a 19th century curiosity for SfM photogrammetry with Li), and Clitheroe (survey for structural monitoring of the historic lime kilns using P40 laser scanner and TST ). Having experience with the techniques and equipment from my own internship in Digital Documentation, it was great to see how the Geospatial team use the same technology to tackle similar problems. I’ve left York full of new ideas and keen to try them out in future projects.

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Which brings me to the end of the week, when I was so lucky to be invited to Historic England’s visit to the Natural History Museum Research Labs in London. We spent the day touring the Imaging and Analysis labs and hearing about the amazing research that takes place there. I could probably write an entire post about this, but for now just 2 words (or 5): SEM photogrammetry. Dramatic pause. Also, confocal microscopy, CT scanning, 3D modelling. It was an absolutely fantastic experience and a perfect ending to my week with Historic England.

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During the last 2 weeks, most of my time has been spent working on a BIM model of the Palace at Edinburgh Castle. This subject definitely deserves its own post, so stay tuned. The building has undergone many phases of development and alterations, which have resulted in an extremely complex structure – geometrically, but also functionally. Creating a BIM model for this type of building is not straightforward, even with the advantage of having a complete point cloud as a basis for modelling.

Having had the opportunity to follow this project all the way from laser scanning on site to data processing and registration and now to modelling in Revit, I can see that creating a BIM model for the Palace will be a great asset for in-depth understanding of the structure, the way the building works, and the way it has changed over time. The model is being developed in-house by HES and requires the coordination of different teams and disciplines. Eventually, when both structural and M&E information is added to the architectural model, we will have a complete picture of this building from a single source – probably for the first time ever. More on the Palace BIM project to follow within the next few weeks.

The Palace block, Edinburgh Castle. Screenshot of the point cloud in Recap.

 

Coastal erosion monitoring at Skara Brae, Orkney

I have just returned to Edinburgh after an adventurous 4-day fieldwork trip to Skara Brae in Orkney, using laser scanning to determine the degree of coastal erosion on the Bay of Skaill around the neolithic settlement. To do that, a 3D survey of the site is conducted every 2 years and the data compared to determine the changes in the position and shape of the sand dunes forming the edge of the coast.

 

Due to limited time on site (and adverse weather conditions) 2 teams were working at the same time on the beach using the Leica P40 and C10 scanners and survey control using traverses and GPS. The C10 was used to scan the top of the dunes on the east of the village, in a traverse tying to scans along the beach (see photos).

 

The weather was not in our favour (low temperatures and high winds), but the work was completed in time. The data is being processed at the moment and the comparison with the 2014 scans will reveal the degree of erosion on the coastline.

Edinburgh Castle Palace Scan2BIM

March was a very busy month for the Digital Documentation team. Much of our time has been spent laser scanning the Palace block at Edinburgh Castle for a scan-to-BIM case study by Historic Environment Scotland. The idea is to create an BIM or AIM (asset information model) of the Palace block to be used for the subsequent management of various aspects of the building’s function.

Laser scanning is the primary method of survey for the building fabric (architectural elements), but it will be supplemented by additional surveys. The laser scanning survey is guided by the Asset Information Requirements document, which specifies areas of interest/priority and required levels of detail per category. The goal is to achieve 100% coverage of both exterior and interior spaces.

According to the AIR document, some of the least “glamorous” areas of the building, such as boiler rooms, electrical cupboards, switch rooms, and attic spaces have a higher priority for the model than some of the high-profile exhibition areas for example. This means that a lot of our time on site has been spent crouching inside tiny cupboards and boiler rooms surrounded by pipes and cables. These areas tend to be confined spaces full of equipment, difficult to navigate (or even to set up the scanner) and usually need a lot of scans to get good coverage and avoid shadows or data voids. Although we do not have to scan every last surface inside a boiler room, the AIR document makes it clear that at least the general dimensions and position of all equipment will need to be visible in the resulting point cloud.

In this project, multiple scanners have been used. The Leica P40 produces clean, crisp data with considerably less noise over great distances, but is very difficult (or impossible) to set up inside any of those tight cramped spaces. Therefore, all the cupboards, boiler rooms, switch rooms, etc were scanned with a Faro Focus 3D, which has a much shorter range and produces noisy data, but is significantly smaller, a lot lighter, and can easily fit inside any of those spaces. The same scanner was used in the attics, which were accessible through a folding ladder and generally very tight spaces, difficult to navigate when carrying any sort of equipment. Using the Faro proved very successful in those areas (on a photographic tripod or sitting directly on the floor).

Laser scanning an attic at Edinburgh Castle Palace with a Faro Focus 3D. Ghostbusters uniform to be worn at all times, as per the risk assessment report. 

Registration of the data has been progressing along with the field work. More on that to follow very soon…

 

Cleaning scans in Cyclone

Registering scans from the Great Hall in Edinburgh Castle has been a great opportunity for clarifying certain aspects of the registration process in Cyclone: mainly, the effect of cleaning scans for cloud alignment and registration.

Some laser scanning manuals and practice guides advise that cleaning scans prior to registration can have a positive effect when cloud alignment is used as a registration method. That means removing “bad data”, such as speckle noise or moving objects (cars, people, trees). In the Great Hall project, the effect of cleaning scans was apparent in the cloud-to-cloud alignment statistics  (mainly looking at RMS values). The improvement could also be verified visually: registered clean scans present “crisp” surfaces, in contrast with the noisy, “fuzzy” result from the original scans.

It must be noted that manually cleaning scans can be very time-consuming depending on the number of scans, amount of noise and geometry of spaces/objects. Using features like the limit box or various sections/slices through the point cloud can help to identify, isolate, and remove bad data. Cleaning scans is more important when the main registration method is cloud-to-cloud, as the results depend entirely on the effectiveness of the ICP algorithm and overlap between scans.

Deciding when to clean is also important: immediately after importing scans (before any kind of registration) or half-way through (e.g. after putting scans together with minimum number of cloud constraints, but before auto-adding extra constraints)? In some cases, it was very useful to first quickly register the scans without cleaning. This will not produce the best registration result, but was good enough for identifying data voids or other problems. This initial registration can be done before the data acquisition phase is over and even on site: additional scans can be done without having to return to the site later. After this initial registration phase, the scans can be properly cleaned and the registration updated to work with the clean point clouds.

This process has been followed for the Great Hall registration as well as other projects and has shown good results. The initial registration was in some cases performed using the auto-alignment option in Cyclone, for which the software calculates the relative positions of the scans automatically on import. The results are never perfect: usually, auto-alignment creates several distinct groups of aligned scans that then have to be registered together. That’s usually the best case scenario – although in some cases Cyclone has been able to successfully auto-align smaller projects (small number of scans, very good overlap). In other cases, however, the auto-alignment is just plain wrong: the software fails to match the correct surfaces together, resulting in a jumble of unrelated scans. For this reason, the constraints created by the auto-alignment process should be checked manually. Note that looking at the statistics of the cloud alignment algorithm is not always enough: sometimes constraints with RMS value <<10mm are actually completely wrong when checked visually. Still, the auto-alignment feature has proven extremely useful especially in larger projects, because it can save considerable amounts of processing time. In some cases, however, (perhaps when overlap between scans was rather low) it made more sense to completely disregard the results of the cloud-alignment and start fresh, as trying to fix the constraints would take more time than creating them from scratch.

The correct procedure for cleaning scans before registration in Cyclone is not as straightforward as one might imagine. This is mostly due to the complicated structure of Cyclone databases; one needs to understand the hierarchy and relationships among ControlSpace, ModelSpace, ScanWorld and Scans. After much experimentation and communication with Leica support, it has been determined that in the latest version of Cyclone (9.1.3), the cloud alignment algorithm works with the point cloud inside the ScanWorld’s ControlSpace, not with the ModelSpace or Default Clouds. However, in the registered ScanWorld, it is the Default Clouds that appear for each individual ScanWorld. Which can be useful in some cases, but also very confusing. Do you clean in the ModelSpace or ControlSpace? And if in the ControlSpace, which ControlSpace?*

*Cyclone creates a “child” ControlSpace for every time the ScanWorld appears in a registration within the database.

As it stands at the moment, the process for cleaning scans is as follows:

  1. In the tree view, go to each ScanWorld’s ModelSpace and clean unwanted objects.
  2. Select the clean point cloud and make it the ScanWorld’s Default Cloud.
  3. Delete point clouds from the ControlSpace(s).
  4. Go back to the clean ModelSpace, select clean cloud and Copy to ControlSpace(s).

This process will ensure that (a) the cloud alignment algorithm will use the clean clouds (from the ControlSpace), therefore improving registration results and (b) any new ModelSpaces created, as well as the registered ScanWorld ModelSpace, will contain only the clean clouds (Default Clouds).