Volumes of history: volume calculation from 3D sections at the Tell Leilan City Gates excavation

What is the degree of approximation that we can accept in a work related to volumetric data from an excavation? Answering this is not easy because, until laser scanners decrease in price, we will continue to have to interpolate data to obtain surface and volume measurements. As a result, we need to fix a standard for the digital survey of surfaces that will be processed in 3 D managing environments in order to help surveyors gather the data needed for IT operations and to encourage excavators to document their fieldwork with more precision. An Electronic Total Station survey allows enough precision, if we take care to fit our surveyed points grid to the different slopes of the stratigraphic units, increasing the number of points where the surface is discontinuous and decreasing it where the ground flattens. Using a surveyed point grid variable from 120 to 5 points/sqm. (i.e. from 1 point each 10 cm to 1 each 50 cm) according to the sloping of the soil, ensures that the final digital surfaces will be of a high quality. Recently I surveyed the entire excavation of the Garamantian site of Fehwet, Libya (ca. 100 sqm.) by total station using such a standard and am working on the digital reconstruction of the stratigraphic units with good results. But what if there is no chance to respect this standard? In this paper we will describe our experience in the rescue excavation of the City Gate complex in Tell Leilan, Syria where, due to logistical problems, (the distance of the city gates from the main focus of the project, the acropolis, and the inability of the surveyor to be in both places at once) we could not survey the surfaces of the stratigraphic units, but instead surveyed the sections enclosing the excavated area.