3D Photogrammetric Survey of Alina’s Chapel, Oystermouth Castle

Posted on May 22, 2021 by Black Mountains Archaeology

We were recently asked by Taliesin Conservation to undertake a high resolution, metrically accurate 3D photogrammetric survey of Alina’s Chapel, Oystermouth Castle (SAMGm007) ahead of conservation work. The survey was undertaken with a camera equipped UAV (drone) and tied into the Ordnance Survey National Grid and Datum using an RTK GN55/ Glonass (GPS) Receiver.

Oystermouth Castle is located on a high carboniferous knoll overlooking the town and Swansea Bay. The castle dates to the 12^th century, probably built by William de Londres after Henry de Beaumont of Warwick’s conquest of Gower in 1107. The RCAHMW (2000, 249) note at least six phases of masonry development at Oystermouth (RCAHMW 2000, 245-272).

The castle most likely started as ringwork before being replaced by stone keep by Maurice de Londres (1138-41) (Period I).

John de Braose (1220-32) constructed the central block, a two-storeyed structure over a vaulted cellar set against the north wall of the keep (Period II).

Period III may post-date the Welsh attack on Gower in 1256. The northwest block and west range being added.

William de Braose II (1241-90) likely built the gatehouse and curtain walls, finished by the time Edward I visited the castle in 1284 (Period IV).

The chapel block (Period V) consists of the finest masonry in the castle and likely dates to the 14^thcentury. Before construction it was necessary to demolish part of east curtain wall. The chapel consisted of a basement, used as a kitchen, first floor apartment and second floor chapel lighted by five decorated windows. The largest eastern window divided by two chamfered mullions and cusped and interlaced tracery (RCAHMW 2000, 245-272). The roof of the chapel forming a crenelated parapet. The chapel may have been built by Alina de Braose (1327-31), daughter of William de Braose III and widow of John de Mowbray.

Period VI consisted of the construction of several ranges set against the southwest and east curtain walls. The east range being a kitchen of some kind with excavations in 2009 (Sherman 2012, 6) recovering stone and slate roof tiles and a shell midden containing large quantities of oyster, periwinkle, muscle, limpet whelk and pod razor shell all potentially dating to the 13^th/14^th centuries.

The survey generated a dense point cloud over 97 million points with a mean RMS error of 0.013m. Six GCPs were used and surveyed with an EMLID Reach GN55/ Glonass (GPS) Receiver and data logger with a sub-20mm error margin to OSGB36 (National Grid). The Ground Sampling Distance (GSD) achieved was a great 0.84cm/pixel.

You can view the 3D photogrammetric survey of Alina’s Chapel here. A high resolution still from the 3D model is below.

3D Photogrammetric Orthographic of Alina’s Chapel, Oystermouth Castle

With thanks to:

We are very grateful to Taliesin Conservation, Swansea Council and Cadw for help and support during the project.

References

Newman, J, 2001, The Buildings of Wales, Glamorgan. Second Edition. University of Wales Press.

RCAHMW, 2000, An Inventory of the Ancient Monuments in Glamorgan Vol III – Part lb Medieval Secular Monuments The Later Castle From 1217 to the Present. Aberystwyth.

Sherman, A, 2012, Recent archaeological works at Oystermouth Castle: Archaeological evaluation, community excavation, watching brief and window recording. GGAT Report 2012/071.