Vol. IX, No. 2

August, 1996

Pompeii in 1996

H. Eiteljorg, II

Fig. 1 - Mr. Hanna at the total station
in the Eumachia Building at Pompeii.
Fig. 2 - Hidden line drawing of portion of west
interior wall, Eumachia building. See Fig. 1,
at left, for a photograph of this wall.

The 1996 season at Pompeii was quite different from the 1995 season. Photogrammetry was not used, and the remains surveyed all were within reach of someone on the ground or on a ladder - with the help of our fishing pole and remote target. As a result, each day's survey data could be downloaded from the data collector, and there was no need to wait until a later time to turn the data points into parts of a computer model. That, in turn, encouraged us to transfer each day's survey data into the computer and to create the relevant portion of the model from that data before going back into the field. We couldn't have kept up with the data if we had surveyed all day, but we learned that data from four or five hours of surveying in the morning could generally be turned into parts of the model after about the same amount of time working with the computer in the afternoon.

The results of this way of working - spending the time from about 8 a.m. until noon or 1 p.m. in the field and the afternoon and early evening in the "office" making the model - were a small data backlog and a much greater sense of the pace of the work as themodel grew.

Our work was also helped by the survey aids that had been made before leaving for Pompeii. The acrylic plate used to position the prism - either the standard prism or the mini-prism - came in very handy. It was much easier to resurvey precise points that had been surveyed before and to be certain that the prism lay in the same position each time we returned. It was also easier to position a prism directly over the corner of a stone, even if the stone had been abraided.

The target that was made this year to attach to the fishing pole turned out to be even more valuable than we had expected. That target was simply a clear plastic ruler with reflecting tape on its back surface. A clamp to attach it to the fishing pole was included but could be completely removed. Both red and gray reflecting tape were used, and the tape was positioned so that the color changed at points 10 cm. and 20 cm. from the tip of the ruler, and the tape stopped at the 30 cm. mark. That made it possible to take two readings, neither of which was at the tip of the ruler but both of which lay on a line a known distance from the tip (10 cm., 20 cm., or 30 cm. from the tip). Those readings could be taken even if the instrument was quite a distance from the target.

Figs. 3 and 4 - The two survey aids at work in Pompeii. At left, in Fig. 3, the plate for holding the prism pole is shown. Mr. Hanna is holding the mini-prism on the corner of the step with the aid of the plate. At right, in Fig. 4, Mr. Hanna holds the reflecting tape target. Note that the right end is out of view, but the change of color of the reflecting tape at the 10 cm. mark is visible near Mr. Hanna's right thumb, as are the second change of color and the end of the tape, 30 cm. from the tip, near Mr. Hanna's left thumb.

From those two readings it was possible to construct the position of the tip of the ruler with the CAD system. That worked well, as I had thought it would, but another use for the ruler markings was just as valuable. We realized that, so long as the ruler was vertically oriented, we could read from any point along its edge, note the height from the tip of the ruler by reading through the telescope of the total station, and adjust the reading accordingly. That meant that when we were close enough to read the dimensions on the ruler with the telescope on the total station, we could take readings for locations that were not difficult to reach but were impossible to see. In particular, we were able to survey ground points that lay behind large building stones by simply adjusting the elevations of the surveyed points to account for how far off the ground the reading was taken - a distance we could read directly on the ruler/target.

The target worked well on the fishing pole as well, making it possible to take readings of points very far off the ground. Indeed, on one occasion, I was unable to see the points as I was maneuvering the fishing rod and target. My movements were guided either by Mr. Hanna or Project Director John J. Dobbins until the position of the reflecting tape was correct. Then the reading could be taken.

We did have a problem with our software this year. The process of sending data from the data recorder to the computer did not work correctly, though we were able to find a work-around. That was distressing, and we have not determined the nature of the problem. Part of the problem may be related to the use of Windows NT on a laptop, since the program cannot find the serial port when the computer is away from the office.

For other Newsletter articles concerning the applications of CAD modelling in archaeology and architectural history or Pompeii, consult the Subject index.

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