One of the main aims of the European project named "Cultural Heritage Through Time" (CHT2) was to fully integrate the fourth dimension (4D) of time into 3D models for analysing structures and landscapes over time. The results obtained by working in accordance with the below scheme were the basis for web publication (Fig. 1).
Fig. 1. Diagram of data processing, modelling, and integration [D. Gonzalez-Aguilera, (Ed.), "Methodology Definition/4D Visualization, in: Cultural Heritage Through Time" CHT2 WP2, U., 2016. WP2: Salamanca University (USAL), Spain, pp. 25.]
Historical data included plans, maps, drawings, pictures, photos (Fig. 2) and descriptions, which were of a great value for the 3D reconstruction of objects and their correct visualisation. Historical models were prepared by history specialist.
Fig. 2. Examples of current and archival data used in the process of modelling objects of the Krakow Fortress: a, b - archival maps (Fort Batowice, Fort Łysa Góra), c,d,f - archival plans (Fort Bastion III, Fort Kościuszko), f - archival aerial photo (Fort Kościuszko), g - archival drawing (Fort Sudoł), h - current picture (Fort Sudoł), i - actual orthophotomap (Fort Kościuszko), j - topographic map (Fort Kościuszko).
To develop models presenting current state of chosen Forts, modern measuring techniques were used. One of them was terrestrial laser scanning (TLS). We used for instance Z+F Imager ® 5010C (Fig. 3). The registration of entire complexes was possible thanks to the UAV flights (Fig. 4). The Phantom 3 Professional - DJI device was equipped with digital camera. There were also Airborne Laser Scaning (ALS) involved.
Fig. 3. Terrestrial laser scanning
Fig. 4. Phantom 3 Professional DJI quadrocopter with a FC300X (FOV f/2.8 94° 20mm) camera
Collected data for the current state of the objects were automatically processed with the Agisoft Photoscan software as many times as it was necessary to successfully implement 3D model in a website portal. The input data are 2D image data with additional informations. Processing 2D > 3D is going on as follows: creation of point cloud, mesh, texture. Metric 3D model is obtained from non-metric data. Next model is simplified and validated until the result of this process is satisfactory (Fig. 5).
Fig. 5. Diagram of data processing for publication in a website.
So far mentioned online publication of 3D data was the final stage of the research in the CHT2 project. Different IT solutions were tested, not only those commercial ones (Hexagon Geospatial Portal, CityEngine WebViewer) but also free technologies as X3D, 3DHOP. Main conditions that were to be met by the portal are the following:
- Maintain georeference of a model;
- Preserve as much metric properties as needed, which would serve as a basis for quantitative analyses, to ensure quick and errorless loading of the website;
- Meet high visualisation demands in order to use photorealistic models in future possible commercial applications;
- Create multiple layers for each model visualizing the same object but from different period of time to enable identification of occurred changes;
- Attach additional archival materials, such as old plans, maps, drawings, photos etc., that would serve other important information;
- Find other useful functionalities of the portals that would be engaging for the user.
eXtensible 3D developed by not-for-profit Web3D Consortium is “a royalty-free, platform-independent, open-standard file format and run-time architecture to represent and communicate 3D scenes and objects. X3D is an ISO/IEC internationally-ratified standard.” . VRML (Virtual Reality Modelling Language) format, replaced by X3D (Extensible 3D), was needed for the 3D scene to be uploaded on the X3D portal. There was no errors with exporting the model to this format. The problem was with the appearance and no functionalities of the portal, which was unsatisfactory and did not meet the project requirements.
3DHOP (3D Heritage Online Presenter) “is an open-source software package for the creation of interactive Web presentations of high-resolution 3D models” . The solution is perfect for small-sized objects, not for 3D scenes of landscapes since there is no possibility to publish georeferenced models and maps. Another limitation was an internal NXS format generated from PLY file with a texture atlas in a single file. Nevertheless, the 3DHOP portal enables e.g light control and measuring length – properties that were not available in X3D and are among the project requirements.
Hexagon Geospatial Portal was a good solution for online visualization of large city models with generalized geometry. However, it was not well adopted to the publication of mesh models, as it is in the case of the model of Fort Citadel 2 “Kościuszko”. Another issue was the conversion of the model into an internal myVR format that was carried out in mTransformer by myVR Software AS (a part of Hexagon) because the quality of the texture drastically decreased. Despite the wide variety of functionalities available e.g. many layers including base maps, basic spatial analysis and measurements, light control (Fig. 6), Geospatial Portal had to be disqualified – the poor visualisation was outweighing. All the same Hexagon Geospatial Portal is very promising.
Fig. 6. Interface of Hexagon Geospatial Portal.
CityEngine WebViewer meets the most of the requires criteria for a publishing technology: operations on the common formats such as OBJ and DAE, georeferencing, layers sorted in groups, swipe view, ortophotomaps and DTM, light control. The results you can see below (Fig. 7 and Fig. 8).
CityEngine from Esri transforms 2D GIS Data into Smart 3D City Models possible to share thought time in Internet. The solution, as grounded on GIS assumtion has no problem with other geospatial data: vector, raster (DTM, ortophotomaps) etc. The main concept of CityEngine is a procedural approach to effective modeling. Encrypted procedure contains a number of commands regarding the geometry of the objects. Instead of the classic user operation who manually develops models, the task is described "abstract" in the rules file. CGE (Computer Generated Architecture) shape grammar is unique programming language with specification of generating objects architectural. The the idea is to define rules in CityEngine, which iteratively creates more and more details. After creating the 3D city model, model can be exported to * .3ws, CityEngine format Web-Scene, and published in the Internet using free module CityEngine or on ArcGiS Online platform.
CityEngine supports input model formats: .dae, .fbx, .kml, .kmz and .obj. The following ArcGIS Online formats can be used for data export: Esri Scene Layer Package .slpk, CityEngine Web 2WS .3ws, 360 VR Experience 3VR. In our research .obj was applied as an input and .3ws as an output format.
Fig. 7. Desktop Internet visualization – Fort Kosciuszko (2 stages are available 1850-5, 2017).
Fig. 8. Mobile device Internet visualization – Fort Kosciuszko (2 stages are available 1850-5, 2017 in parallel analysis).
Open-sources or free soultions for 3D/4D model and point clouds visualization are available as desktop application and also as web application
Web sharing of 3D models in time using GIS data is not common.
After testing commercial software Hexagon and Esri solution based on Esri – CityEnigine was selected for initial web publication:
- data preparation was easy;
- there was no problem with texturing;
- City Engine Viewer is free;
- the solution works also on any mobile device;
- available very useful tool for 4D models comparison (screen is divided by two parts and user can shift the arrow loking at the 2 models parallel).