Data copyright © Harrison Eiteljorg, II unless otherwise stated
Center for the Study of Architecture
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Harrison Eiteljorg, II (2013) The CSA Propylaea Project [data-set]. York: Archaeology Data Service [distributor] https://doi.org/10.5284/1022574
Harrison Eiteljorg, II
The CSA Propylaea Project began in 1999 as an idea. It grew out of the confluence of various events: my experience with AutoCAD as an aid to work on the older propylon (the predecessor to the Propylaea on the Acropolis), Dr. Tasos Tanoulas' and my friendship (we had known each other for more than a decade by then), Maria Ioannidou's technical interest in both the Propylaea and CAD as well as her position as engineer for the Propylaea work, my complete confidence in Tasos' skills and experience as a student of the structure, and Tasos' confidence in my skills with AutoCAD. (Note that all of us who worked on this project became friends in the course of the work; therefore, the use of first names after the introduction of individuals with proper full names will be the norm in this short history. Indeed, I called Maria Ioannidou Mary, not Maria, so her name may occur in either form here.)
The first steps in the direction of the project were taken by sending to Maria a laptop PC with AutoCAD and getting her started in learning to use the program. Since her husband was an architect, this seemed an especially good way to begin. In addition, her position as engineer made her the person in Athens with the larger direct role to play.
As the plans coalesced, we determined to make a formal proposal to the Samuel H. Kress Foundation, at least in part because the Kress Foundation had been instrumental in helping Tasos and me get to know one another better by sponsoring him as a Kress Lecturer for the Archaeological Institute of America. As was so often the case, Susan C. Jones, my valued colleague for fourteen years at CSA, was very helpful in the preparation of the grant. Indeed, Susan's help throughout was generally unsung but truly critical.
An important piece of the puzzle was the publication by Tasos, Maria, and A. Moraitou of the volume entitled Study for the Restoration of the Propylaea (Vol. I) in 1994. I do not know when I first realized it, but the drawings of two of the walls of the NW wing of the Propylaea in that volume included explicit x-, y-, and z-coordinates for each corner of each block that survived well enough to be measured. That level of documentation made it possible to consider modeling the building — stone-by-stone — with relative ease and speed.
On March 15, 2000, I paid a visit to the Kress offices and met with Ms. Lisa Ackerman, then Vice President and Chief Administrative Officer of the Foundation, to discuss the ideas of the project. After some refining, a proposal was submitted later that spring and approved in June. It had been read and refined by myself, the CSA board, Tasos, and Maria. A copy version of the proposal may be found in this PDF version of the proposal. The proposal emphasized not only the ground-breaking nature of the project based on the core use of digital technology but also the level of international cooperation and the ultimate creation of a public resource on the web for the data derived from the work.
The proposal envisioned a young architect working in Athens more or less full-time and using the information from the survey work already done by the Propylaea crew. It also envisioned Maria as the primary responsible person in Athens, with Tasos needing to play only a more limited role. However, before the project could get started, there were shifts in the committee in charge of work on the Acropolis, and Maria ultimately became the Chairwoman of the Committee for the Restoration of the Acropolis Monuments and Director of the Acropolis Restoration Service. This left her with virtually no time for work on the project. Fortunately, Tasos indicated that he was more than willing to take up a larger part of the work as a result, but his time was still limited, and his main focus had to remain on the restoration work on the building.
Fortunately, Tasos had met Chrysanthos Kanellopoulos and introduced us. Chrys is an archaeologist with considerable expertise both as a field archaeologist and as a user of digital technologies, and he was then working with computer colleagues on various archaeological projects. Chrys' dual experience in the field and at the computer were precious. Given Maria's effective departure from the project and the changes that entailed, it seemed more efficient and probably conducive to higher quality results if we contracted with Chrys and his colleagues to do the modeling rather than trying to find and train a young architect. A carefully specified work agreement was reached, and Chrys and his colleagues were able to create a model of the SE anta of the central structure of the Propylaea in rather short order. They were able to use various sources of information, specifically scans of engineering-style drawings of the individual blocks that had been removed from the wall, drawings of the wall surfaces, and Tasos' occasional help as well. Chrys scanned the drawings, and we used the need to make the scans as a natural lead-in to an experiment on scanning requirements. (The results were published in the CSA Newsletter, "Scanning Drawings for Preservation and Display - What Resolution?" XIII.3; Winter, 2001; and in a follow-up article, "Scanning Propylaea Drawings," XIV.1; Spring, 2002.) Chrys' archaeological sensitivities were often critical in this work since he recognized issues that would have been missed entirely by computer specialists without archaeological experience. On the rare occasion when we had a difference about the CAD work, our views were informed by the archaeological issues, not just computer questions, making discussions fruitful and productive.
The CAD work was excellent. As I said in the report to the Kress Foundation (March, 2001) on this work: ". . . this is one of those typically complex Periclean walls that present problems of geometry. The anta leans out (to the east) and also inclines toward the center of the building, to the north. The wall diminishes in thickness as it rises. Nevertheless, the top and bottom surfaces of all blocks are (or were originally) horizontal. As a result none of the blocks is a simple geometric shape; each must be individual modeled. Dealing with them was not easy, but I have been very impressed with the results, and the experience of Mr. Kanellopoulos and his team with AutoCAD means that they have operated much more as collaborators than as employees, making the results, I believe, even better than they might otherwise have been."
The same team worked on the column of the east facade of the central structure, and that model is also included in the data files of the project.
The full team did not, however, continue; the CAD modelers working with Chrys were very frustrated by the demands of the work. They "were frustrated by the requirements and academic approach of this work. The documentation needs of the scholarly processes were incomprehensible to them. As a result, they were unwilling to continue." I must take some of the blame for this since it was I who tried to explain the documentation needs. However, I believe that most of the problem was simply that our needs were far more burdensome than those of commercial customers who were prepared to pay for their services.
Chrys continued to work with another CAD expert and eventually worked on two other parts of the project on his own. He used Tasos' drawings and notes to produce a model of the roof of the NW wing based upon Tasos' reconstruction. That work resulted in a joint paper presented to the CAA (Computer Applications and Quantitative Methods in Archaeology) meetings on Crete in 2003; though we were co-authors, the base CAD work was all Chrys' work. He also used Tasos' drawings to try to make a model of the Ionic capital of one of the columns of the central passageway. This effort, however, was not successful, and Tasos was very disappointed.
At that point we turned our attention to the NW wing of the Propylaea, the so-called Pinakotheka. This was the wing for which Tasos had provided such impressive drawings in the publication mentioned above.
It was possible to make fully three-dimensional (surface) models of the two walls that had been fully documented in the book (and, in the process, to find specific factual errors resulting from the need to measure, record, and copy by hand). In fact, that modeling work was automated before the project had formally begun and was then refined as a part of the project work. (See "Using a Spreadsheet to Speed AutoCAD® Data Entry," XIII.1; Spring, 2000; and "A Spreadsheet as a CAD Aid – Again," XIV.2; Fall, 2001.)
A sidelight of considerable importance here. I had clearly not explained to Tasos and Maria the nature of 3D CAD and the need for survey data that would provide all three coordinates (x, y, and z) of any point to be used in a model. At the same time, I had mistakenly assumed that the kind of survey work evident in the drawings of the NW wing referred to above was universal in the building. As it turned out, however, most walls had been surveyed only as elevation views of the walls in question. As a result, there was generally no dimension for the depth of a point within the wall. That is, the elevation of a corner of a block would be measured, as would the distance along the face of the wall on a horizontal axis. What was not routinely measured was the extent to which a given point protruded from or was sunk into the "normal" surface of the wall, the third dimension. This was the case because there was no perceived need for the third dimension when dealing with walls that appeared to be stable and in no danger of collapse. The two walls included in the publication with all three coordinates had suffered from damage and were in some danger; only because of that were they surveyed with all three coordinates.
The critical misunderstanding about the nature of the extant survey data had a dramatic effect on the project. Rather than being a relatively simple modeling effort, it ultimately had to become a survey project. That is, it was necessary to survey walls in order to model them; necessary to obtain all three coordinates of each point of interest. This was not the plan or expectation, but it became the reality.
To summarize the results of this misunderstanding, we had to determine how to survey and then to carry out the survey work — to mm. precision in keeping with Acropolis standards — on the walls of the Propylaea, finding and obtaining all three coordinates of all points of interest. While that may seem a relatively trivial problem, it is most decidedly not when the requirements include both such precision and blocks that have suffered over the centuries. Delays in obtaining permission to do this unanticipated work, coupled with the difficulties of having various members of the team working in different places with differing primary responsibilities, made progress toward solving the survey problems all the more erratic. CSA Newsletter articles discuss the attempted solutions and the problems encountered, and this is not the place to repeat the information. See the list of project publications for various articles on this problem, starting with "Surveying the Northwest Wing of the Propylaea -- A Pilot Project," XVI.1; Spring, 2003.
The most obvious potential solutions were both technological — the use of a total station surveying instrument (alone, without hand-held targets) and the use of desktop photogrammetry (as opposed to stereo photogrammetry, which requires surveyed targets distributed in the field of view as well as simultaneous photographs from a precisely measured distance apart). Neither was effective for, in retrospect, simple and obvious reasons. However, the use of the total station brought into the project another person whose participation has been of great help and who, like the others involved, has become a friend as a result of the collaboration: Manolis Kapokakis. Manolis is more than an experienced and skilled surveyor. He is also a thoughtful and practical problem-solver willing to look "outside the box" for solutions and to think broadly about possible new approaches.
A total station, which can survey points at a distance and (only for newer versions of the instruments) without a target placed in position at the aim point, cannot survey a point that no longer exists, a point eroded away by time and weather. There is nothing to aim at, nothing for the infrared, distance-determining beam to reflect from. Since virtually all corners of blocks in a building like the Propylaea have suffered from such erosion, using the total station effectively required some form of target at any point to be surveyed. That is, a target had to be positioned by someone standing near the aim point, holding the target in the place where the corner once was. Using a total station without hand-positioned targets could not provide the level of precision required. (While it might have been possible to calculate corner points with carefully-gathered other data, using a total station without a target also assumes that fine discriminations can be made while looking through the telescope at the blocks on the wall. However, such visual discriminations via the telescope are simply not fine enough, as we learned in time.)
Photogrammetry also came up short. In the case of photogrammetry it should have been possible to locate points that would permit the interpolation of eroded corners. The problem lay with finding points that could be identified in multiple photographs, and the whole theory of photogrammetry (either stereo photogrammetry or desktop photogrammetry, though the user of stereo photographs does not see separate images but a merged stereo image) is based upon finding the point to be surveyed in multiple images. Since there was not a sharp shadow or blemish near every corner, there was often nothing to permit the computer operator to pick a specific point to be surveyed in one photograph and then find the same point in another photograph to complete the measurement.
These experiments left us with no alternative but to find a way to hold targets at the points to be surveyed, that is, to put a person up on some supporting platform next to the wall so that the person could place a target in position and hold it while a total station operator on the ground took a reading of the target. A so-called man-lift, operated by various personnel on the Acropolis for work on the buildings and graciously made available to us, was used to help in the effort to survey in this way in October of 2003. It was brought into the NW wing and positioned in various places so that a person could be lifted to reach various points along the vertical path of the machine's lifting platform.
The man-lift worked very well, making it possible for us to provide a well-positioned target and to survey that target from the ground. Details may be found in CSA Newsletter articles, and it is worth noting here that the design of the target was very important. The design shown in "A Final Survey Experiment on the NW Wing of the Propylaea," XVI.3; Winter, 2004; has many important details. As good as the experiments were, the man-lift had significant drawbacks. It was not steady as it got higher, and it could not be positioned safely in corners. (The machine had outriggers to prevent tipping, and we over-rode some safety devices when getting close to corners, but not all the safety devices could be over-ridden. In addition, of course, over-riding the safety devices carried certain risks that would have been more worrisome for use beyond the initial, short-term experiment.) I should mention here the participation of David Scahill in the experiments with the man-lift. David worked on the project relatively briefly, but his contribution was important.
Although the man-lift showed that a standard survey process would work, there seemed no reasonable way to position a person at every location where a target needed to be held. In addition, it was sometimes difficult for the person on the lift to position himself and the lift platform such that the total station operator could have a clear line-of-sight to the target to see it and take a reading; the higher the lift, the more difficult that problem became. (The seeming obvious solution, a ladder, presented various problems. The key difficulty was that using a ladder would require virtually constant movement of the ladder and that, in turn, would have required a Propylaea workman, perhaps more than one, to be assisting us at all times we were working, an impossible disruption of the work on the building.) That led us to try another — new and still expensive — technological approach, a 3D scanner. As we now know, a 3D scanner faces the same problem as the unaided total station plus another. That is, a 3D scanner cannot survey eroded corners either (but it can potentially gather many points that can be used to define the missing corner), but, more problematic, it surveys only the points that happen to fall on the grid intersections determined by the machine calibration, not by the real world at which it has been aimed. That is, the points actually surveyed are chosen by the machine via a simple grid unrelated to the real world. As a result, it might or might not actually survey the points most needed for this work. It should produce excellent results for some kinds of blocks but not for the cut-stone, marble masonry of the Acropolis in the Classical period. If the needed corners – or points that can be used to interpolate the positions of the corners – are not "hit" by the scanning beam, the data are of limited value. As a consequence, the results were not adequate for the precision required on the Acropolis. (Although our experiments were not successful for this project, the effort was one that needed to be made. We are very grateful to Michaelis Lefantzis, an archaeologist then working on the Stoa of Eumenes on the South Slope of the Acropolis, and his colleagues in that work, Vassilis Pagounis and various employees of Tension S.A. Without their aid, this experiment could not have been carried out.)
At that point the project moved into a very low gear indeed. We found that there were blocks from the north wall of the central structure that could be modeled, and a young graduate student, Apostolis Kassios, was hired to do that modeling. He had considerable experience with making models of buildings from Thera/Santorini, and he did an excellent job with the blocks from the north wall. (I failed to provide Apostolis with the same specifications document that I had provided to Chrys and his colleagues; so there were some differences in approach that resulted.)
While that modeling was being done, I was trying to find a way to deal with the problem that I might call "the archaeologist on the wall" issue. We needed to find a reliable, inexpensive way to get someone up on something secure next to walls so that targets could be positioned for surveying. (Another seemingly obvious possibility — scaffolding — could not be used in this building by a crew whose aims were unrelated to the major reconstruction being undertaken. In addition, traditional scaffolding would present so many support pieces in the field of view that it would be virtually impossible for a total station to have an unobstructed view of the points intended for survey.)
Some of my early experiments were potentially useful, but most of the earliest ones were sadly unproductive. Of particular note, my attempts to figure out a way to use PVC piping to construct some kind of simple tower that could support either a person or, as a last resort, some form of stereo photogrammetry gear, were laughable and sometimes dangerous. During this time I also engaged the services of a small engineering firm, Chatten Associates, in nearby West Conshohocken, PA, to assist. They designed a kind of portable target holder on a stick that never quite seemed ready for real use. A designer recommended by them provided some smaller, practical ideas but nothing that added up to a useful product.
I got close to a design that entailed a post that could be pushed up to the wall and attached to a kind of large, soft clamp that would hold it to the wall without risk of damage to the masonry. It was to hold stereo-photogrammetric equipment. It seemed good enough that a description was sent to Maria and Tasos. At that point, thankfully, I happened upon a work site where a kind of portable scaffolding was in use. It seemed to offer promise, and I followed up, finding that the scaffolding was made in Scranton, PA., by the Alum-A-Pole company, which has been very generous and helpful in assisting us as we developed the use of their system for our decidedly non-standard application.
The scaffolding has been fully described in CSA Newsletter articles, beginning with "An Apparatus to Aid in Surveying High Walls," XX.3; Winter, 2008. It was tested and various problems were encountered, most of them revolving around the difficulty of raising the scaffold post from lying on the the ground to its final vertical position. Given the length required for using it in Athens (as long as 42 feet), considerable force was required to raise it.
Although I had first seen the scaffold in use in the fall of 2006, it took more than a year to get from a possible problem solution to a real one and to arrange an acceptable time to try the resulting solution. In December, 2007, it was put to work in Athens. (The experiment required shipping the equipment from the U.S — after packaging it in somewhat unorthodox fashion — and arranging its delivery to the Acropolis, paying the surprisingly high duty assessed, and then having it hoisted onto the Acropolis by a crane.)
The test was short and simple, and it was a success. However, the test was meant only as that, a test, and further development was required. Additional work was needed because the method for raising the posts had proved imperfect and because a more generic version of the set-up seemed to be in order. Manolis noted that, if the scaffolding could be raised without a rope going over the wall, the system would be more flexible, working on covered as well as open walls. (This was one of those occasions when Manolis' practical approach to our problems was evident and important. The value of designing a system that could be used under a roof or ceiling as well as for an unencumbered wall was clear to all — after Manolis' comments.)
Further work in the U.S. yielded a fully-refined design for a simple machine to raise the post that was well-tested, stable, inexpensive to build, and simple. (Once again, there were some comic moments — and a few slightly dangerous ones — with less successful approaches in the interim.) It was easily constructed from simple 2x4 lumber, plywood, rope, pulleys, a commercial winch, and chain. I set out for Athens, according to plan, in October of 2008. The work plan called for constructing two of the machines for raising the posts previously sent to Athens, putting the entire system to work, and making measurements.
Unfortunately, just prior to my departure from the U.S., Tasos informed me that the Acropolis workmen required to assist with the project (men from his work crew) would not be able to assist because of pressing work on the Acropolis. I went anyway, with the hope that a more explicit plan could be arranged and that a return trip in the spring could follow. I also thought that it might be possible to prepare more thoroughly for buying the necessary materials by finding vendors in Athens in person. (Attempts to obtain materials over the internet had not been productive, and a wider range of items than we could even locate over the internet was required.)
It was clear to me during the time in Athens that something had changed, though it seemed atmospheric rather than factual. Only after my return to the U.S. did I learn that Tasos had determined that data gathered by the project and at the project's expense in the future would necessarily be considered the property of the Greek government and could only be made available to people as the Ministry of Culture might from time to time determine. Attempts to modify that change were unavailing; so the project could not continue according to the terms of the original proposal, with data being made available on a website without restrictions. As a result, active work on the CSA Propylaea Project stopped, though generating the various documents now available continued. Unused funds from the Samuel H. Kress Foundation have been returned with our gratitude and our regret for being unable to complete the project. (In fairness, it must be said that, given the need for surveying and the costs entailed, a complete CAD model could almost certainly not have been created with the funds remaining.)
This short history of the project is one of the documents that comprise the results of the work.
A good many lessons were learned in the course of the project.
Although the survey work was not anticipated when the project began, the various experiments we conducted, especially those involving one or another technology, were very valuable. They are not applicable to an extremely broad range of structures, but they are certainly applicable to buildings made of carefully cut stone where the dimensions of individual blocks truly matter and where precision surveying/documentation is required. The CSA Newsletter articles about the survey work, especially the articles comparing various methodologies, should stand as an important product of the project.
In particular, the scaffolding system that was created — a combination of a commercial system and the machine for lifting it into place — should be useful to many scholars in the future, whether working on cut-stone structures such as the Propylaea or simply needing a close look at a wall.
The work on the roof of the NW wing also stands as a useful product. As a CAD model, it permits users to understand much more fully the way the ancient roof must have worked. This, of course, was primarily the work of Tasos Tanoulas prior to the beginning of the project.
The other CAD models are also valuable, though their incomplete nature reduces their utility.
Not discussed in the history of the project was the use of a relational database to aid in the construction of the CAD model of the NW wing. A CSA Newsletter article; "From Field Data to CAD Model: Modeling the NW wing of the Propylaea," XVII.1; Spring, 2004; has been written about this. In addition, both "Parametric Modeling in AutoCAD® -- Almost" XVII.3; Winter, 2005; and "Using Old Data in New Ways," XXII.3; January, 2010; deal with the issue. The use of the database was extremely important both as an aid to the CAD processes and as a way to preserve both the data from which everything descended and the processes that lead from the data to the CAD model. That is, the database is a kind of data-and-process source that should let anyone reconstruct the work that led to the CAD models.
The use of the database is, however, only one part of a larger story that I believe we have been trying to tell. Digital data present scholars with the opportunity to repurpose data in many ways, never needing to type or otherwise copy information for a new purpose. Taking advantage of that capability, however, requires that scholars be conversant with more kinds of digital technologies than is likely in today's world. Making that point to scholars has not been a stated purpose of the project, but it is a point that the project will continue to emphasize via the CSA Newsletter and other venues.
Although the expected range of project data has not been created, the website nonetheless shows how effectively the data from a project can be shared. Files can be made available; images can be served at various resolutions, and raw data can also be exposed to inspection. These were the aims of the project, albeit with less actual data available than expected. Nevertheless, the data available should illustrate the ways this level of data sharing can work.
There were certainly negative lessons as well.
The changes in the project plan were unavoidable in the sense that, given the basic misunderstandings about survey needs, there was simply no opportunity to accomplish the original goals without doing a great deal of unanticipated survey work. That, in turn, meant that we needed permissions that had not been expected and that we needed a far greater level of cooperation from a far wider group of officials than had been expected. These things do not lead to lessons learned, but they inform our discussion. They also explain why, once the new needs for surveying had been encountered, obtaining permissions tended to be unusually difficult and time-consuming.
I have many regrets, and I will try to keep them brief.
I should have learned modern Greek well. Having never spent more than two-and-a-half weeks in Greece at a stretch, my comfort level with modern Greek is very low. Had I known the project would go on for so long, . . . . Since Tasos and Maria and everyone else with whom I worked closely spoke better English than I could ever have learned Greek, I had little obvious need. Nevertheless, I should have made a more sincere effort, if nothing else, as a demonstration. (I had actually learned more Greek than my colleagues knew but was reluctant to use it in conversation with them where it would have served only to embarrass me.)
I should have found some ways to overcome the physical distance between us, with my colleagues living and working in Athens while I was so far away. That physical distance too often led to a kind of psychological distance as well. In the earlier days in particular, email was completely unreliable for my colleagues, and telephoning was always somewhat problematic because of the time differences. (Indeed, I always called Manolis on weekdays, not including Fridays, at 11:00 pm, his time, because it was a good time for me, 7 hours behind, and a time when he was always at work alone and therefore able to talk at length and without interruption.) Getting together without an agenda simply did not happen, and that meant that keeping things on an even keel was not simple. There were occasions when people were simply not on the same wave-length, and those occasions were hard even to recognize, much less to deal with when we were not together.
Given the change in the project aims and work requirements, I probably should have planned more regular trips to Athens just to get together. Instead, I felt that any trip, to justify the cost, had to have specific goals.
I suspect that I should have done more to keep people in Athens abreast of the work going on here at the Bryn Mawr office and at my home nearby, particularly when I was trying to work out the surveying equipment. Since I got no questions from my colleagues, I assumed that they were too busy to worry and did not want to be bothered with regular reports. Meanwhile, they had no way to know of all the time spent seeking a suitable survey process or that, for some years, my most common last thought before sleep at night and first one in the morning was about the current attempt to find a useful survey device. As a natural result, they saw my work as irregular and inconsistent, and I saw them as interested only when needing to answer an email or finalize a plan.
To be clear, I do not think I should have rushed the work. The various attempts to solve the survey problems were not, in my view, soluble with a push to reach a solution on deadline. Absent some sort of unlimited budget for ridiculously hi-tech devices, I do not believe we could have found better solutions or found the solutions we did find much more quickly. (I say that with some confidence because of the attempt to use professional engineers to assist — to no avail.)
Finally, there were at times frustrations, with my colleagues apparently feeling left out of the decision-making process. While I understand the frustrations, I am reluctant to take all the blame here. By and large, I was the only one trying to make plans or to suggest ways to move the project forward. I do not believe I ever summarily rejected anyone else's proposals for work on the project. Nor do I believe I obliged others to work on the project in ways that they did not approve.
One technical lesson should be mentioned. The versions of AutoCAD used for this work did not permit what is called parametric modeling, that is, creating a model based upon stored operations and dimensions such that any dimension or operation can be changed and the modeling process repeated with the changes made. As a result, when using AutoCAD to model something very complex, something likely to require changes, it is worthwhile to save versions of a model separately, one version for one set of procedures and another version for the next set and so on. This permits the model-maker to return to any step in the process and to start again from that point. While I understood the need, I did not insist upon the use of such a system. To the best of my knowledge, it only damaged work one time, but that was one time too many.
It must also be said that the specifications for data files were never as full and complete as they should have been. Working, as we were, in uncharted waters, we did not anticipate clearly the various issues that could — and did — complicate dealing with the data. For instance, the CAD modelers often used cross-referenced files, something I will not permit for reasons discussed in various other venues. However, I had not made it clear in advance that such files should not be used. As a result, I was obliged to spend a great deal of time re-working the files. As the use of technologies like these becomes more common, such specifications must be developed and applied more rigorously.