The last 3 months of hard work culminated yesterday in us carrying out a terrestrial 3D laser scan (TLS) of the cottage and surrounding buildings in Proleek. The day was a great success and we were absolutely blessed with the weather (I conclude that the weather is always better in County Louth!). The outcome, a truly amazing scan of the site and buildings. A massive thanks to Ciara from Farrimond MacManus (Archeological surveyors based in Belfast) and Conor, a surveyor from Queens University, who helped out on the day, for their tireless work on a Saturday. Farrimond MacManus specialise in archaeological and heritage surveying and scanning, finding on a regular basis, such things as ring forts and bronze urns! Respect.
First I got a a crash course in TLS from Conor. We used a tripod mounted, Leika C10 scanner, working our way around the outside and interior of the structures. It was interesting to see the automation and manual activities involved and the concentration required to ensure correct triangulation of the survey points. The guys talked about ‘scanners fatigue’ which I assume is a direct result of not breaking for lunch (as exhibited on the day)!
It was rather contradictory to see this R2D2-like machine in a pre-famine building. My Aunt has offered the thought of the people who originally constructed the vernacular structures, looking to the present day and seeing the interest in their simple home. Conor has a theory that someone in Leica’s product development team had been a Promethius fan. In the sci-fi movie, the sentinel robots scan a cave with a laser beam, projecting the shape of the cave into a point cloud. However in the movie the beam is red. Conor explained that the colour actually doesn’t matter. It could be purple for all the scanner was concerned. All are eye safe beams too!
Some tech stuff…
The LiDAR registers 500,000 points per second. In total, we completed 19 x 360 degree scans (below) with 100mm accuracy at 100m. Therefore, over 100 metres distance from an object, the laser picks up a point every 100mm. This becomes more dense with proximity. Therefore, at 50m a point is gathered to 50mm accuracy. Since we carried out most of the scan at a distance of around 2-5m from the building, we produced a point cloud of the building with a point every 2-5mm!!!! The scanner also took photographs, which will later be mapped onto the points scanned, producing a colour realistic scan.
Ciara is a licenced Archaeologist and had some fascinating observations throughout the day. By studying the stone coursing, she offered an explanation as to the chronological construction of the various sections of the house. According to Ciara, the house was likely a single storey bungalow. Dating the masonry elements in the upper floor, she concluded that the upper floor had been a later addition to the dwelling. Although at this point we are making at best, educated guesses as to the phasing, it is clear that the building has undergone numerous fabric changes throughout its lifetime, spanning multiple centuries.
Following the day of surveying, the various scanned areas will be merged together by matching the registered targets on the site. To give an idea of the type of information which will be yielded following this post production please see below
- Section cut through the main part of the house (notice the ground level)
- Site plan (points picked up over 100m away!)
- The building from above (notice the floor joists and rocks outside!)
This point cloud data will then be used to proceed with the project planning digitally.