Page 173 - Green - Maritime Archaeology: A Technical Handbook. 2nd ed

152 Maritime Archaeology: A Technical Handbook, Second Edition
measurements were made to all of the other points (17), then the second point was selected and measurements were again made to all remaining unmeasured points (16), and so on, until all measurements were completed.
These data were then transferred from the record matrix to an Excel spreadsheet and saved in a csv format so that these data could be imported directly into Site Surveyor. This method was slightly faster than using these data input interface in Site Surveyor where the interpoint measurements require the 18 points to be set up and then the 162 measurements entered in Site Surveyor graphically, which is time-consuming.
These data were processed in Site Surveyor with the base of the tower acting as the coordinate system. Point 1 was the origin, point 3 was the X- axis, and point 7 the Y-axis. By fixing these three points it was possible to nominate the coordinate system. Thus point 3 was given X equal to the dis- tance from 1 to 2, Y = 0, and Z = 0. Point 7 was given Y equal to the dis- tance from 1 to 7, X = 0, and Z = 0. The program was then run and the residuals examined. It was noted that one measurement (3 to -7 = 3.826) had a residual of 0.995, almost certainly a misreading of 2.826. Ignoring this measurement and a second poor quality measurement, the adjustment gave an average residual (AR) of 0.004 m and RMS residual of 0.006 m. Tran- scribing and processing data took about 30 minutes.
4. Site Surveyor Under Water (Interpoint Survey)
The underwater survey was conducted in the same way as on land, with a pro forma recording sheet and the same tape measures. The tower was erected and then the survey was carried out taking 86 minutes (the shorter time probably reflects the fact that under water it was easier to measure to the high points on the tower than on land where a ladder was required).
The same processing procedure was used, however, the results produced more errors. All measurements with residuals greater or equal to 0.100 m were ignored (15 measurements), the largest outlier 3 to 4 = 3.00 had a residual of 1.998 m, obviously a misreading of the distance 1 m. The other errors were inexplicable and were due to either transcription or measure- ment errors. Presumably, the number of errors reflects the difficulty in recording under water compared with on land. The resulting adjustment gave AR = 0.006 m and RMS = 0.008 m. Transcribing and processing data took about 30 minutes.
5. Site Surveyor Under Water (Control Point Survey)
In this situation, five control points were established a few meters away from the base of the tower and the intercontrol point measurements were