Estimating the Reliability of Digital Data Acquisition in Cultural Astronomy

Abstract

Digital tools are increasingly used in cultural astronomy, so that it is now more important than ever to assess their precision and reliability, and to identify what uncertainties they may introduce. The present work aims to address these issues by comparing a dataset of orientations of Roman cities in the Iberian Peninsula measured in situ with measurements of the same structures obtained through different digital tools. By this, it is possible to estimate the errors that using these techniques introduce and to establish precision limits to data in future work. The results of this preliminary study are then implemented in an archaeoastronomical research project in North Africa, where some on-site measurements had been made in previous fieldwork campaigns by members of the group prior to the current political unrest that now prevents work at some sites in the region. In these instances, Google Earth Pro (2017) and HeyWhatsThat (Kosowsky 2012) have been key tools that have allowed us to complete a survey stretching from present-day Morocco to Libya, as well as to extract a preliminary outline of orientation trends in Roman Africa.

Astronomy in Roman Urbanism: A Statistical Analysis of the Orientation of Roman Towns in the Iberian Peninsula

“…The adequate precision of this tool has been estimated in a previous study. 31 Measurements with HeyWhatsThat are indicated with an asterisk in Table 1, and we introduced a B (blocked) in the altitude columns when resolution of the terrain model did not allow to drawing the horizon properly. Attending to an astronomical quantity (in this case the corresponding geocentric declination of these orientations, which is independent of the geographic coordinates and the local topography) becomes virtually imperative owing to the astronomical nature of this analysis.…”

Establishing a New Order: The Orientation of Roman Towns Built in the Age of Augustus

“…The digital images were normally obtained through the repository Google Earth (GE) and the DTM were accessed via the web application www.heywhatsthat.com (HWT). The accuracy of such measurements depended a lot on a number of considerations (Rodríguez-Antón et al 2017) and the error estimates on declinations for such measurements had to be determined individually. In general the error estimate was nearly ±1½º although on occasions it could be larger.…”

Astronomical Alignments of Paleo-Christian Basilicas in Romania

“…For cross check we have also used Google Earth to measure azimuths following the same approach. Google Earth provides an average error of 1˚ [11]. The error of the digital compass on the smartphone is higher and equal to approximately 2.8˚ [12].…”

“…Out of ten sites, five have horizons with an elevation greater than 1˚ in the direction of the alignment: Adamclisi (3.69˚), Capidava, (2.61˚), Halmyris (1.51˚), Niculițel (2.59˚), and Troemsis (1.5˚). Heywhatsthat provides higher errors for close horizons but lower for distant ones mainly due to the low spatial resolution which triggers loss of information and accuracy for close targets [11]. The mean error of the tool is of 0.5˚.…”