Studio 727 preserving cultural monuments with most modern technology
The project “Digitally Monument Found“(DMF) was brought to life in 2012 by the Operational Programme Information Society (OPIS). The ambition of the project was to digitise selected national cultural monuments and historical objects of the Slovak Republic to be able to make detailed restorations and to preserve these monuments for further generations. In the course of the project DMF, from 2012 to 2015, 1,855 architectural cultural monuments, such as castles, churches, cloisters, monuments, castle ruins and historical town districts, were completely digitised by STUDIO 727.
Various digitisation measurement technologies were used, like terrestrial laser scanning (TLS), digital photogrammetry (DP), and were combined with aerial photos from helicopters and UAVs. There were also used in conjunction with conventional measurement technologies, such as Global Navigation Satellite System (GNSS). To be able to process the resulted data volume, new software was developed to accommodate the large volume and merge the picture and laser scan data together into a model (TLS - DP linking).
The results of the digitisation of the cultural monuments are 3D-models, point clouds, highly exact polygon models, orthophotos and technical drawings with accuracy up to 1 centimeter.
UAVs were used to digitise big buildings and areas as well as hard-to-reach areas, like steeples, roofs and facades. To digitise larger areas, helicopters were used.
To achieve the ambitious goals of the project in the planned time, the OPIS assumed commercial partnerships with external partners. One of the leading partners, decisively in the success of the project, was STUDIO 727.
STUDIO 727 started working on the DMF project in 2013. During the two-year project term, STUDIO 727 digitised 81 big monuments included in the overall 1,457 historically important objects. With the digitisation of the monuments, STUDIO 727 used a combined workflow from TLS and DP, going from the ground to the air.
While collecting the data, the most modern technologies and sensors were used. The laser scan data was collected with the Leica ScanStation P20.
The photogrammetric data were collected with different cameras. With the TLS, digital pictures of objects and buildings with a high metrical accuracy can be captured in the shortest time. A challenge of the production of 3D models from TLS data is that in spite of the high point density, small details of the architectural elements cannot be shown according to the demands when the distance is great between the laser scanner and the object. To reach the demanded detail, TLS and photogrammetricdata are brought together in later steps.
To obtain the detail needed in the project and to digitise far-away objects, TLS data needed to be combined with photogrammetry. The advantages with photogrammetry are the accessible degree in details and the realistic reproduction of the colours. A disadvantage from the photogrammetry is that the model can be distorted or deformed during the reconstruction. In this project, two different methods of photogrammetry were used. In the robotic imaging with a tripod, the camera is mounted on a programmable robotics panorama tripod. In picture 4, you can see a Rodeon VR station HD that brings the camera in given positions and triggers the camera. The second procedure is without a tripod and is called a handheld image.The best results are reached from a combination of both photogrammetric methods.
The aerial photos of big areas and hard-to-reach places were captured with the Aibot X6 V2 in combination with the Nikon D810. The flights were executed to a large part with autonomous flown waypoint flights. The flights were planned in the office with the flight planning software Aibotix AiProFligt after the inspection of the monument. Then the flight mission was executed by a twoman team (pilot + operator). For detailed images of important structures, the flights were flown manual with the Aibot X6 V2. In these cases, the pilot took over the control of the UAVs and the operator took control of the Gimbals and the camera. To generate the demanded data amount and the detailed degree, the camera was automatically triggered every two seconds. Not required pictures are sorted out.
The challenge of the processing of the accumulated data was to develop a workflow that processes automated laser scan and photogrammetry data, and which can handle the large data volume. The solution for this challenge came by the software company of CapturingReality. CapturingReality developed a software solution (RealityCapture) which did justice to the demands.
Before the TLS data could be processed with RealityCapture further, this data had to be preprocessed with the software Leica Cyclone. With Cyclone, the laser scan data was georeferenced, merging the required point clouds and converting the data into the required .ptx data type. Cyclone distinguishes the highest possible level of automation.Cyclone offers the possibility that point clouds can be exported in CAD and be processed there directly, such as for ground plans or 3D drawings.
With RealityCapture, the georeferenced point clouds and pictures are merged in an automated process. For this, the most suitable data (laser and image data) will be selected. From this data, the point cloud will then be generated. The resulting point cloud combines the advantages of both methods. The further processing of data occurs in JTSK coordinate system, the default coordinate system in the Slovak Republic. From this, the point cloud can then be processed into orthophotos, polygonal models and 3D models with high accuracy and a high level of detail. Furthermore, RealityCapture can create an alignment report from any data source. Depending on the size of the monument, the required level of detail and the scale, the process time of a complete, highly accurate 3D model can be several months. In the table below are three different sized monuments that were digitized related to data volume and processing time (the times include the alignment, meshing and colouring for final models).
The advantages of this workflow of the digitization of cultural monuments over the classical geodetic methods are the temporal factor with the data collection as well as the highly detailed degree in connection with a high accuracy. Based on the obtained data, any required documentation of the monument can be created, for example a faithful restoration or even rebuilding. It is no longer necessary to pre-define the output, because all required documentation can be created from the collected data.
In this project, 1,855 historically relevant objects of the Slovak Republic were digitised successfully. The results achieved in the project were so impressive that the project was extended for five years. During the next five years, 500 objects should be digitised, preserving these monuments for future generations.