Archaeological survey using GPS at RCAHMS

Archaeological survey using GPS at RCAHMS

The Royal Commission on the Ancient and Historical Monuments of Scotland (RCAHMS) undertakes an archaeological recording and mapping programme across the whole of Scotland, targeting areas on a strategic basis. The aim is to add to and improve the quality of the information held within the National Monuments Record of Scotland (NMRS), and to provide the Ordnance Survey with selected="selected" new or improved archaeological depiction for base-scale mapping. Survey data is checked="checked" and edited before being transferred to the publicly accessible NMRS geographical information system. This resource is used by archaeologists involved in planning applications, research students and the general public. The data may also provide the basis for RCAHMS publication maps or illustrations.

Prior to the implementation of GPS at RCAHMS in 1997 mapping was carried out using total stations, with local map detail surveyed to position our divorced surveys on the National Grid. GPS not only presented many obvious advantages in terms of field practice but also allowed our work to be fitted directly to the National Grid - removing the inaccuracies which occur when fitting to map detail.

In order to use GPS, however, an expensive, time consuming and resource intensive control network had to be undertaken in each survey area. Observations from a trig station network were taken to fix our reference station and to compute the transformation parameters to convert from WGS84 to OSGB36®. This transformation could then be applied to all kinematic work. Unfortunately, any errors in trig coords would adversely affect the quality of results.

The Ordnance Survey National GPS Network will allow RCAHMS to make huge time and resource savings in controlling its GPS field survey. The active network will be used to establish the EtrS89 coordinates of a local reference station. Kinematic surveys will then be processed against this position, and the results transformed using the online coordinate converter to obtain OSGB36 coordinates accurately and consistently without actually occupying any Ordnance Survey control stations.