Pt. 637.1m (SO 267 322) - Uchaf reclassifed to 500m Sub-Uchaf
There has been a reclassification to the listing of Yr
Uchafion instigated from analysis of LIDAR data by Aled Williams and subsequently confirmed via a survey with the Trimble GeoXH 6000. Yr Uchafion is the draft title for a list of
the Welsh 500m P15s that takes in all hills in Wales at or above 500m that have
a minimum of 15m of drop, the list is a joint compilation with Aled
Williams. Details relating to this list
were published on the Mapping Mountains site in November 2015.
The hill is situated in the Mynyddoedd Duon (Black
Mountains) group of hills in the eastern part of the Parc Cenedlaethol Bannau
Brycheiniog (Brecon Beacons National Park) in the Region of South Wales (C-3)
and is situated on the most easterly of the main elongated ridges of this hill
range with Waun Fach (SO 215 299) being its Cardinal Hill, and it is positioned
above the small community of Capel-y-ffin to its south-west and the Olchon
Valley to its east and the Vale of Ewyas to its south. The hill can be accessed on good paths from these
two valleys or from its south-east or north-west via the Offa’s Dyke Path that
follows the ridge crest.
As an appropriate name for this hill is not in the
public domain it is being listed under the point (Pt. 637.1m) notation, and its
reclassification from an Uchaf to a 500m Sub-Uchaf is due to the analysis of LIDAR
data. LIDAR (Light Detection & Ranging) is
highly accurate height data that is now freely available for much of England
and Wales, and the hill was first analysed with
this data by Joseph Nuttall, independent of this, Aled also analysed LIDAR data
using a slightly different method and ascertained the details for this hill’s
reclassification.
If Pt. 637.1m does not
have the minimum of 15m of drop it would be taken out of the listing of Welsh
hills at or over 500m in height that has a minimum of 15m of drop, and has the
working title of Yr Uchafion, and if having between 14m and below 15m of drop
the hill would be classified as a 500m Sub-Uchaf.
Aled’s analysis of LIDAR data gives the hill the
following details:
Pt.
637.4m
Summit
Height: 637.4m (converted to OSGM15, and middle of three equivalent height points)
Summit
Grid Reference: SO 26696 32273
Bwlch
Height: 622.7m (converted to OSGM15)
Bwlch
Grid Reference: SO 26711 32628
Drop: 14.7m
As the stated philosophy for our co-authored lists
is to take the most accurate data available on any given day, and as Ordnance
Survey map data uses a 637m summit spot height attained from an aerial survey
that has a prescribed margin of uncertainty of +/- 3m applicable to it and as
the previously listed bwlch height is based on contour interpolation, it is viewed that LIDAR data is sufficient to reclassify this hill as it is quoted as having a prescribed margin of uncertainty of +/- 0.15m.
Therefore, the 637.4m LIDAR data produced for the summit position at SO 26696 32273 and the 622.7m LIDAR data produced for the bwlch position at SO 26711 32628 is insufficient for this hill to retain its Uchaf status, with the details from the Trimble GeoXH 6000 survey being 637.1m (converted to OSGM15) summit at SO 26709 32261 and also SO 26695 32273 and 622.5m (converted to OSGM15) bwlch at SO 26710 32627, and therefore with 14.5m of drop Pt. 637.1m is reclassified to a 500m Sub-Uchaf.
Therefore, the 637.4m LIDAR data produced for the summit position at SO 26696 32273 and the 622.7m LIDAR data produced for the bwlch position at SO 26711 32628 is insufficient for this hill to retain its Uchaf status, with the details from the Trimble GeoXH 6000 survey being 637.1m (converted to OSGM15) summit at SO 26709 32261 and also SO 26695 32273 and 622.5m (converted to OSGM15) bwlch at SO 26710 32627, and therefore with 14.5m of drop Pt. 637.1m is reclassified to a 500m Sub-Uchaf.
This now revises the total in Yr Uchafion which will be
updated accordingly and the hill is now listed as a 500m Sub-Uchaf.
The full details for the hill are:
Cardinal Hill: Waun
Fach
Summit Height: 637.1m
(converted to OSGM15)
Name: Pt. 637.1m
OS 1:50,000 map: 161
Summit Grid Reference:
SO
26709 32261
Drop: 14.5m (converted to OSGM15)
The reclassifications to Yr Uchafion / The Welsh 500m P15s
reported on Mapping Mountains are as follows:
UCHAF ADDITIONS
UCHAF RECLASSIFICATIONS
Pt. 637.1m (SO 267 322) Uchaf reclassified to 500m Sub-Uchaf with
14.5m of drop.
UCHAF DELETIONS
 |
| Pt. 637.1m (SO 267 322) is now reclassified from an Uchaf to a 500m Sub-Uchaf |
Myrddyn Phillips and Aled Williams (November 2016)
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