This post provides an introduction to 3D recording and photogrammetry in the context of cultural heritage.
The recording of measurements and documentation has long been a process used by archaeologists to record fragile archaeological sites and excavation processes (Pollefeys et al. 2). Indeed, evidence is often disturbed or destroyed during the excavation process itself (Pollefeys et al. 2). Moreover, archaeology has relied on graphical documentation through “maps, excavation drawings, matrices and photographs”, and relied on “methods of presentation that are essentially two-dimensional” (Campana 7). One of the fundamentals behind the creation of 3D objects from 2D images is based on the concept of stereoscopic vision. For example, although human eyes are placed close together, nonetheless, both eyes see from different angles. The brain processes this information into one picture “interpreting the slight differences between each view as depth” (Speck). Thus, stereoscopic vision is the image perception from each eye which produces “a three-dimensional picture: one with height, width and depth” (Speck).
3D data is recognised as “a critical component to permanently record the form of important objects and sites so that, in digital form at least, they might be passed down to future generations” (Remondino 1104). The 3D recording of cultural heritage artefacts has several benefits. It allows for “the generation of very realistic 3D results (in terms of geometric and radiometric accuracy)” (Remondino 1105). The 3D results are then used for such purposes as
- Historical documentation;
- Conservation and preservation of the original artefact (interaction without handling, decreased risk of damage);
- Cross-comparisons with similar objects in terms of colour, texture and shape;
- Optimising restoration techniques;
- Creating simulations for aging and deterioration;
- Visual display of artefacts in multimedia exhibitions or web-based exhibitions;
- Virtual Tourism (Remondino 1105; Remondino and El-Hakim 269).
- 3D printing, i.e. additive manufacturing for research and educational purposes (Neumüller et al. 115)
Even with the availability of low cost computers, the advances in producing tools and software to create 3D models, and the ease of access to the Internet to display such models, “the generation of a precise and photo-realistic computer model of a complex object still requires considerable effort” (Remondino and El- Hakim 269). In order to acquire accurate and reliable 3D data, deliberation needs to be given to the workflow beforehand (Redmondino and El-Hakim 274). Questions like the type of camera to be used, the angles to be considered for obtaining a full representation, and the types of software required need to be considered as part of the approach when designing a workflow. Choosing the right software may ultimately depend on cost, the technical abilities of the user and the availability of suitable documentation to support the products. Often, the design phase of the workflow will consider the setting of the object, whether it is indoors or outdoors or whether it can be moved to a more appropriate location. For example, in a museum setting the design of the workflow will depend on the availability of museum staff to assist in the handling of the object, as this will determine whether the object can be turned upright to capture the base.
Other things to consider when planning the workflow are the management and conservation of the final 3D models, and the preservation of the data used to allow for the retrieval of such information for use in other applications for educational and further research purposes (Remondino 1105; also Pletinckx and Tartessos 34). Remondino adds that “standards, comparative data and best practices are also needed; to show not only advantages but also limitations of systems and software” (1126). From this, it seems clear that the actual production of a 3D model should not be the solitary outcome. Rather, the documentation of the workflow in terms of capturing the data (or a rationale for the data selected for input), the processing methodology for the selected data, and the preservation and retrieval of the selected data for re-examination are equally important in terms of an outcome.
There are various methods used to produce 3D models in the cultural heritage sector, and methodologies will vary depending on the approach and tools used. According to Campana, “survey and documentation, as well as photography, present not an alternative to reality but an interpretation of reality, whether it be of an object, a context or a landscape” (7). Moreover, “a good interpretation relies on a clear understanding of the object itself, and of its essential characteristics” (Campana 7). Over the past two decades laser scanning and digital photogrammetry have emerged as important additions in providing “extraordinary potential for promoting a revolution in the documentation and recording of archaeological evidence and in its subsequent dissemination” (Campana 7). Nonetheless, such innovations do not necessitate “a revolution in the field of archaeology generally” (Campana 7). Rather, Campana suggests that “[t]o play an active role in such advances a technique must be developed in such a way as to answer to the real needs of the archaeologist” (Campana 7). In contemporary settings, museums have also taken to using “robust digital imaging practices” through the “selective extraction of information from a sequence of standard digital photographs” (Mudge et al.). The extraction of information from the photographs is “selected by computer algorithms” and “integrated into a new digital representation containing knowledge not present in the original photographs” (Mudge et al.). This process is part of an emerging science and is more commonly known as Computational Photography (Mudge et al.).
The term ‘photogrammetry’ is derived from the Greek words phos or phot – meaning light; gramma – meaning a letter or something that is drawn; and metrein – meaning measurement (Schenk 3; Walford). As a concept, photogrammetry has developed in line with science and technology, and its phases of development are “directly related to the technological inventions of photography, airplanes, computers and electronics” (Schenk 7). Schenk suggests that the genesis of photogrammetry can be traced to the invention of photography in 1839 by Daguerre and Niepce, and thereafter through experimentation with “terrestrial and balloon photogrammetry” (Schenk 7-8). It was used by the military in World War II, and later by NASA “to make topographical maps of the moon for the Apollo missions” (Speck). In recent decades it has been applied in various fields from engineering to forensics (Walford; Svatý 121), environmental to forestry (Atlis Geomatics), and cartography to the “precise 3D documentation of Cultural Heritage” (Remondino 1111). While current definitions are debated, Schenk provides a definition below to capture the central concept:
“Photogrammetry is the science of obtaining reliable information about the properties of surfaces and objects without physical contact with the objects, and of measuring and interpreting this information” (Schenk 3).
Remondino and El-Hakim describe photogrammetry as a 3D measurement technique which involves non-contact (269-270). It may be broken down into distinct phases: 1) data acquisition (inputs); 2) the application of photogrammetric procedures; and 3) the creation of photogrammetric products (outputs) (Schenk 4-6). Data is acquired through the use of sensors, such as digital cameras or laser scanners, and the products are derivatives of “single photographs or composites of overlapping photographs” (Schenk 5). Typical outputs include maps, measurement drawings and 3D models of a real-world scene or object (Walford). Photogrammetry may be further classified based on the location of the camera during photography. Aerial photogrammetry indicates that the data was acquired through a camera mounted on an aircraft or drone, while close-range photogrammetry indicates that the camera was hand-held or placed on a tripod close to the object (Walford).
Photogrammetry is considered as a suitable approach for processing image data due to its ability to “deliver at any scale of application accurate, metric and detailed 3D information with estimates of precision and reliability of the unknown parameters from the measured image correspondences (tie points)” (Remondino 1111). It is based on the principle of triangulation to produce 3D point measurements. Photogrammetric software figures out the exterior orientations of the images, that is “where the camera was and what direction it was pointing in when each image was captured” (Adams Technology Team Blog). Then “[b]y mathematically intersecting converging lines in space, the precise location of the point can be determined” (Geodetic Systems). For some time photogrammetry has been reserved for use by experts with expensive sensor equipment, however, in modern day, even a mobile camera phone with up to 5 Megapixels can be used for photogrammetric purposes (Remondino 1111-1112).
In conclusion, it would seem that the creation of a 3D digital object from 2D images is not merely about the production of a final 3D digital illustration, rather, it entails numerous and varied actions from planning the approach, designing a workflow, documenting the capturing and processing procedures as well as ensuring for the preservation of the data and the 3D model for the future.
 Pletinckx and Tartessos suggest that “the key elements are appropriate tools, a reliable and well understood workflow and a successful integration into the relevant institutes and organisations” (Pletinckx and Tartessos 33). Additionally, Pletinckx and Tartessos add that there also needs to be consideration for “the long term preservation of the results and all its sources in a structured way” (Pletinckx and Tartessos 34).
- Adam Technology Team Blog. “How Does Photogrammetry Work?” Web 27 Feb. 2015. <http://www.adamtech.com.au/Blog/?p=102>
- Campana, Stefano. “Archeological Needs.” 3D Recording and Modelling in Archaeology and Cultural Heritage Theory and best practices. Eds. Remondino, Fabio and Stefano Campana, 2014. Web. 04 March 2015. Academia
- Geodetic Systems “The Basics of Photogrammetry.” Geodetic Systems. Web 22 March 2015. <http://www.geodetic.com/v-stars/what-is-photogrammetry.aspx>
- Mudge et al. “Principles and Practices of Robust, Photography-based Digital Imaging Techniques for Museums.” VAST 2010, The 11th International Symposium on Virtual Reality, Archaeology and Cultural Heritage, September 21–24, 2010, The Louvre, Paris, France. Web. 20 Feb. 2015. <http://culturalheritageimaging.org/What_We_Do/Publications/vast2010/vast2010_tu torial_final_print.pdf>
- Neumüller, Moritz et al. “3D Printing for Cultural Heritage: Preservation, Accessibility, Research and Education.” 3D Research Challenges in Cultural Heritage: A Roadmap in Digital Heritage Preservation. Ed. Marinos Ioannides and Ewald Quak. New York; Dordrecht; London: Springer, 2014. 119–135. Google Books.
- Pletinckx, Daniel, and Premio Tartessos. “Virtual Archaeology as an Integrated Preservation Method.” Virtual Archaeology Review 4 (2011): 33. Web. 1 Mar. 2015. <http://varjournal.es/doc/varj02_004_07.pdf>.
- Pollefeys Marc; Luc Van Gool; Maarten Vergauwen; Kurt Cornelis; Frank Verbiest and Jan Tops. “3D Recording for Archaeological Fieldwork.” IEEE Computer Graphics and ApplicationsIEEE Computer Society. Web. 12 Feb. 2015. <http://www.inf.ethz.ch/personal/pomarc/pubs/PollefeysCGA03.pdf>.
- Remondino, Fabio. ‘Heritage Recording and 3D Modeling with Photogrammetry and 3D Scanning. Remote Sensing 3 (2011): 1104-1138;
- Remondino, Fabio, and Sabry El-Hakim. “Image-Based 3D Modelling: A Review.” Photogrammetric Record115 (2006): 269-291. Academic Search Complete. Web.
- Speck, Shane. “Stereoscopic Vision.” HowStuffWorks. Web. 22 Feb. 2015. <http://computer.howstuffworks.com/3d-pc-glasses.htm>.
- Schenk, T. ‘Introduction to Photogrammetry.’ Department of Civil and Environmental Engineering and Geodetic Science, The Ohio State University, Autumn Quarter 2005.Web 01 Mar. 2015.<http://www.mat.uc.pt/~gil/downloads/IntroPhoto.pdf>