Heritage3D

One of the Discovery Programme’s major research projects in recent years has been the study of medieval rural settlement of Ireland. In the course of this project the remains of the 13thC priory in Roscommon town were recognised as being of great interest and a high resolution 3D survey was undertaken, sufficiently detailed to enable the identification of architectural elements of the structure. Having recorded such detailed laser scan survey data, a valuable result itself, the research team then looked to generate a digital reconstruction of how the priory may have looked in medieval times. The reconstruction was primarily based on the laser scan pointcloud ensuring its geometric accuracy, but drew on a wide range of historic evidence and contemporary examples to aid the reconstruction. Having digitally reconstructed the priory itself the next challenge was to reconstruct to local landscape as of medieval times, drawing on a range of sources from historic maps and plans to digital elevation models.
Instruments and software The laser scanner used on the project was a Mensi GS101 time of flight scanner. The instrument was powered by a Kippor Sinemaster 1000 petrol generator and controlled by Trimble PointScape 3.2 hosted on a Panasonic Toughbook CF19. A total of 12 station setups were used and the fieldwork took 2 days to complete. Processing was done using Trimble Realworks 6. Georeferencing of the laser scans was done using a Trimble 5800 RTK receiver operating with the Trimble VRS NOW correction service via a GSM mobile phone link. Electrical resistivity geophysics was done to the south of the priory using a geoscan research RM15 resistance meter. The digital reconstruction of the priory was done using AutoCAD, 3DS max and VUE. ArcGIS was used as a platform for combining all the relevant historic and modern mapping data.
Why was this method of 3d data generation selected? This method of 3d data generation was selected in order to be able to accurately identify all the structural elements of the upstanding remains of the building. The scan data was gathered at a resolution of 10mm or better, sufficiently detailed for the individual stonework of the building to be identified. This level of detail provided the basis for further detailed analysis of the upstanding remains, the basis of the reconstruction of the priory. An example of this was the pitch and extent of the roof. Scars on the walls of the building were picked up in the scan data providing the basis for the accurate modelling of the roof. A topographic survey of the south field of the priory was also undertaken using the Mensi GS101. The ground was scanned to a high resolution, from which a DTM was generated using ArcGIS. This DTM was looked at in conjunction with the geophysics data and historic and contemporary sources revealing strong evidence that a cloister once stood there, and this was added to our model of the priory.
What problems were encountered? A problem encountered with the priory reconstruction was how to extract relevant, manageable data from the complex pointcloud data which would provide a basis for the model. The approach used was to create orthoimages of the upstanding elevations of the building within Realworks that could be imported into AutoCAD. This method was chosen as a means of simplifying the scan data. The complete point cloud was too large and complex to import directly into AutoCAD but by generating the orthoimages of the elevation planes the dimensional accuracy of scan was retained. A wireframe was then created in AutoCAD by tracing around the detail in the orthoimages, such as window and door opening. It was at this stage also that other relevant data gathered from sources such as historic images of the building and the other survey information could be incorporated into the reconstruction. The full extent of the priory could then be modelled. When the model of the priory was complete the next stage was to attempt to place it within a model of its wider medieval surroundings. The main issue for this context model was how to keep all the wider landscape and buildings at the correct scale with respect to the priory reconstruction itself. This was achieved using GIS. The other buildings in the model were created using 3DS max and these were accurately positioned in the model using the evidence present on historic mapping georeferenced in GIS. A DTM for this wider landscape was created in ArcGIS from satellite height data to add an accurate terrain component to our model. For all stages of the reconstruction process emphasis was given to the importance of the empirical survey evidence, ensuring the strongest metric accuracy is retained within the final model.
What were the final deliverables? The primary deliverable of the project was the georeferenced pointcloud, a digital record of the priory as it currently stands. The reconstruction was undertaken as part of a wider examination of medieval Ireland and its results form an important basis for further research and analysis. This process allowed not only for a greater understanding of the construction of the building itself but how it related to its surrounding landscape. Further deliverables include images of the priory extracted from the survey data itself, and images generated from the reconstructions which will be used in forthcoming project publications. A final deliverable was a fly-through video (avi file) of the reconstruction which has been used in project presentations and has helped to provoke debate and discussion which should, in time, feed back into refining the model.
Further information http://www.discoveryprogramme.ie