Coed Bryn Twr (SH 539 400)
There has been a Significant Height Revision to a hill that is listed in The Welsh P15s, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips.
LIDAR image of Coed Bryn Twr (SH 539 400) |
The criteria for the list that this height revision applies
to are:
The Welsh
P15s – Welsh hills with 15m
minimum drop, irrespective of their height, with an accompanying sub list entitled the Welsh Sub-P15s,
with the criteria for this sub category being all Welsh hills with 14m or more
and below 15m of drop. The list is authored by Myrddyn Phillips, with the
Introduction to the list appearing on Mapping Mountains on the 10th
May 2019.
The Welsh P15s by Myrddyn Phillips |
The name the hill is listed by is Coed Bryn Twr,
and it is adjoined to the Moel Hebog group of hills, which are situated in the north-western part of
North Wales (Region A, Sub-Region A1), and
it is positioned with a minor road and the A487 road to its north and the A497
road to its south, and has the town of Porthmadog towards the east south-east.
When the listing that became known as The Welsh P15s was being compiled, this
hill was included in the main P15 list with an estimated c 19m of drop, based
on the 66m summit spot height that appeared on the Ordnance Survey Vector Map
Local hosted on the Geograph website and which was entitled the Interactive
Coverage Map and an estimated c 47m bwlch height, based on interpolation of 10m
contouring between 40m – 50m.
Extract from the Ordnance Survey 1:25,000 Explorer map |
However, it was not until LIDAR became available
that the details for this hill could be accurately re-assessed. The LIDAR (Light Detection & Ranging)
technique produced highly accurate height data that is now freely available for
much of England and Wales.
LIDAR summit image of Coed Bryn Twr (SH 539 400) |
The summit height produced by LIDAR analysis is 63.7m
and when compared to detail on the Ordnance Survey Vector Map Local hosted on
the Geograph website and which was entitled the Interactive Coverage Map, this
comes within the parameters of the Significant Height Revisions used within
this page heading, these parameters are:
The term Significant Height Revisions applies to
any listed hill whose interpolated height and Ordnance Survey or Harvey map
summit spot height has a 2m or more discrepancy when compared to the survey
result produced by the Trimble GeoXH 6000 or analysis of data produced via
LIDAR, also included are hills whose summit map data is missing an uppermost
ring contour when compared to the data produced by the Trimble or by LIDAR
analysis.
Therefore, the new listed summit height of this
hill is 63.7m and this was derived from LIDAR analysis. This is 2.3m lower than the 66m spot height
that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph
website and which was entitled the Interactive Coverage.
The full details for the hill are:
Group: Moel Hebog
Name: Coed Bryn Twr
OS 1:50,000 map: 124
Summit Height (New Height): 63.7m (LIDAR)
Summit Grid Reference: SH 53944 40079 (LIDAR)
Bwlch Height: 46.3m (LIDAR)
Bwlch Grid Reference: SN 53944 40155 (LIDAR)
Drop: 17.4m (LIDAR)
Myrddyn Phillips (August
2024)
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