Phil Saperstein’s and Sarah Murray’s recent article in the Journal of Field Archaeology is remarkably useful for anyone considering using photogrammetry or structure from motion techniques to document an archaeological site. The authors argue that for the efficiency and precision of photogrammetric techniques to make a significant impact on archaeological documentation practices, archaeologists need to demonstrated greater rigor and transparency in the implementation of these techniques in the field.
Their article outlines key considerations for developing more rigorous field procedures for using photogrammetric techniques. For example, the article advocated for the use of coded targets to improve the efficiency of modeling and the accuracy of the resulting images. The authors provide a useful primer on focal length, aperture setting, and camera equipment which is useful to anyone using photography to document buildings, objects, or spaces. Anyone thinking about using photogrammetry in the field should consult this article. I know that I would do things a bit differently had I read this prior to our field work this summer.
There are three interesting things, however, that this article does not really consider, and I think that these speak to certain tendencies in archaeological methodology and, perhaps, how the discipline “works” in the field at a procedural level.
First, it was curious that there was little discussion of actual software in the article. On the one hand, this is understandable. The requirements of a particular software package, of course, are subject to change, and it was probably worth downplaying specific software in the interest of keeping the article timely. At the same time, the authors do make clear that the software that makes photogrammetric images possible is complex and opaque. This article offers a primer on understanding how to make useful images in the field, but it does not extend to understanding how these images are processed. This division remains a key difference between traditional archaeological illustration practices which are relatively more transparent, and our new use of technology to document sites.
Second, the article focuses on field practices and does not extend to the publication and dissemination of the images produced through these techniques. Like the software used to analyze issues, there tends to be a discontinuity between image production, analysis, and publication in archaeology. With the increased use of digital tools in the field and the growing interest and reliance on processed and 3D images offers unique challenges to archaeological publications that continue to emphasize 2D media for technical and traditional reasons.
Moreover, the producing photographs that are also data used in analysis has additional challenge of making sure that the data is available for independent confirmation of the analysis or future study using new and more advanced software. While archaeologists are never obligated to disseminate data publicly, a requirement does exist to archive properly both the photographs themselves as well as the results of photogrammetric analysis. Archiving digital photographs is relatively straightforward using existing standards and technologies; archiving photogrammetric or 3D models offers some new challenges. I’ve tended to see the needs to archive the results of photogrammetric analysis as something that extends directly from its use in the field and maintaining the continuity of metadata for each image is part of carefully executed field work.
Finally, (and readers of this blog know to expect this), I do wonder whether even a technical article like this could benefit from going beyond arguments for efficiency to include a stronger sense for the interpretative goals and potential for this kind of work. Accuracy and precision, for example, are always relative to the interpretive or analytical needs. Field efficiency is likewise dependent upon the desired interpretive outcome.
The authors do present a nice matrix for deciding whether photogrammetry is possible at a site, but this nevertheless depends on the kind of questions that archaeologists are asking. An article focusing on field practices cannot anticipate every possible interpretative outcome, but the authors have extensive experience with these kinds of technologies and could offer some substantive case studies.
In the end, these quibbles are mostly me saying that I’d prefer this article to be different rather than saying that the article isn’t good. It’s really good. Go read it.