Mapping Mountains – Summit Relocations – Y Trichant

Cefn Llanbister (SO 116 733)

There has been a Summit Relocation to a hill that is listed in the Y Trichant, and which was initiated by LIDAR analysis and confirmed by a survey with the Trimble GeoXH 6000, both of which were conducted by Myrddyn Phillips, with the latter taking place on the 03.07.18 in warm and clear conditions.

Cefn Llanbister (SO 116 733)

The criteria for the list that this summit relocation applies to are:

Y Trichant – Welsh hills at or above 300m and below 400m in height with 30m minimum drop, with an accompanying sub list entitled the Sub-Trichant with the criteria for this sub category being all Welsh hills at or above 300m and below 400m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the Introduction to the list and its renaming appearing on Mapping Mountains on the 13^th May 2017.

The name of the hill is Cefn Llanbister and it is placed in the Beacon Hill group of hills, which are situated in the north-eastern part of Mid and West Wales (Region B, Sub-Region B1), and it is positioned with the Afon Ieithon (River Ithon) and the A 483 road to its west and the B 4356 road to its north, and has the small community of Llanbister at its base to the west of the summit.

As the summit of the hill is a part of open access land it can be approached from most directions with public footpaths accessing this land from the west and east, with the most convenient access to the hill via a track that leaves the B 4356 road just to the north of the summit.

When the original Welsh 300m P30 list was published on Geoff Crowder’s v-g.me website this hill was listed with a 373m summit height based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map, with an accompanying note stating 376m at SO GR117732 on 1986 1:50000 map.

Extract from the Ordnance Survey 1:25,000 Explorer map

Prior to LIDAR analysis and the subsequent survey with the Trimble GeoXH 6000 the listed height of this hill had been revised to 376m based on the spot height on the Ordnance Survey 1:50,000 Landranger map.

Extract from the Ordnance Survey 1:50,000 Landranger map

The summit height produced by the Trimble GeoXH 6000 survey is 377.5m (converted to OSGM15) at SO 11690 73303 and its position in relation to that previously given comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies to any listed hill whose summit meets the following criteria; where there are a number of potential summit positions within close proximity and the highest point is not where previously given, or a relocation of approximately 100 metres or more in distance from either the position of a map spot height or from where the summit of the hill was previously thought to exist, or when the summit of the hill is in a different field compared to where previously given, or when the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary that is judged to be a relatively recent man-made construct.  As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 Explorer map is being prioritised in favour of the 1:50,000 Landranger map for detailing these relocations.

The summit height produced by the Trimble GeoXH 6000 survey is 377.5m (converted to OSGM15) and is positioned at SO 11690 73303, this position is not given a spot height on contemporary Ordnance Survey maps and is approximately 100 metres east from where the 376m spot height appears on the Ordnance Survey 1:50,000 Landranger map and 450 metres north-west from where the 373m spot height appears on the Ordnance Survey 1:25,000 Explorer map.   

The Trimble GeoXH 6000 gathering data at the summit of Cefn Llanbister which confirmed the summit relocation of this hill

The full details for the hill are:

Group:  Beacon Hill

Name:  Cefn Llanbister

OS 1:50,000 map:  136, 148

Summit Height:  377.5m (converted OSGM15)

Summit Grid Reference (new position):  SO 11690 73303

Bwlch Height:  335.3m (converted to OSGM15)

Bwlch Grid Reference:  SO 12399 74601 

 

Drop:  42.2m (converted to OSGM15)

For details on the survey that relocated the summit position of this hill

Myrddyn Phillips (November 2018)

Mapping Mountains – Significant Height Revisions – Y Trichant

Cefn Llanbister (SO 116 733)

There has been a Significant Height Revision to a hill that is listed in the Y Trichant, and which was initiated by LIDAR analysis and followed by a survey with the Trimble GeoXH 6000 both of which were conducted by Myrddyn Phillips, with the latter taking place on the 03.07.18 in warm and clear conditions.

LIDAR image of Cefn Llanbister

The criteria for the list that this height revision applies to are:

Y Trichant – Welsh hills at or above 300m and below 400m in height with 30m minimum drop, with an accompanying sub list entitled the Sub-Trichant with the criteria for this sub category being all Welsh hills at or above 300m and below 400m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the Introduction to the list and its renaming appearing on Mapping Mountains on the 13^th May 2017.

The name of the hill is Cefn Llanbister and it is placed in the Beacon Hill group of hills, which are situated in the north-eastern part of Mid and West Wales (Region B, Sub-Region B1), and it is positioned with the Afon Ieithon (River Ithon) and the A 483 road to its west and the B 4356 road to its north, and has the small community of Llanbister at its base to the west of the summit.

As the summit of the hill is a part of open access land it can be approached from most directions with public footpaths accessing this land from the west and east, with the most convenient access to the hill via a track that leaves the B 4356 road just to the north of the summit.

When the original Welsh 300m P30 list was published on Geoff Crowder’s v-g.me website this hill was listed with a 373m summit height based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map, with an accompanying note stating 376m at SO GR117732 on 1986 1:50000 map.

Extract from the Ordnance Survey 1:25,000 Explorer map

Prior to LIDAR analysis and the subsequent survey with the Trimble GeoXH 6000 the listed height of this hill had been updated to 376m based on the spot height on the Ordnance Survey 1:50,000 Landranger map.

Extract from the Ordnance Survey 1:50,000 Landranger map

The 377.5m (converted to OSGM15) summit height produced by the Trimble GeoXH 6000 is not a dramatic increase from the 376m spot height, but does come 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.  As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 Explorer map is being prioritised in favour of the 1:50,000 Landranger map for detailing these revisions.

Therefore, this hill’s new summit height as surveyed with the Trimble GeoXH 6000 is 377.5m (converted to OSGM15) which is 1.5m higher than its updated height of 376m and 4.5m higher than its original listed height of 373m which appears on the Ordnance Survey 1:25,000 Explorer map.

The Trimble GeoXH 6000 gathering data at the summit of Cefn Llanbister which resulted in this hill's significant height revision

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Beacon Hill

Name:  Cefn Llanbister

OS 1:50,000 map:  136, 148

Summit Height (New height):  377.5m (converted OSGM15)

Summit Grid Reference:  SO 11690 73303

Bwlch Height:  335.3m (converted to OSGM15)

Bwlch Grid Reference:  SO 12399 74601

  

Drop:  42.2m (converted to OSGM15)

For details on the survey that significantly revised the summit height of this hill

Myrddyn Phillips (November 2018)

Mapping Mountains – Trimble Surveys – Beacon Hill

03.07.18  Cefn Llanbister (SO 116 733)

Cefn Llanbister (SO 116 733)

Cefn Llanbister is one of those hills that nestles in its place in the world, not making a dramatic fuss like higher hills, or wanting attention from the masses, it stands quietly with its summit a part of common land, visited by local dog walker’s and the occasional passing hill bagger.  It is not a hill that stands out, but it is one of many that is peaceful to visit and gives tranquil surrounds and contentment, and especially so on such a beautiful morning, where blue skies predominated and the early morning warmth was to be savoured, whereas what would become the mid afternoon heat would be soul sapping.

I approached from the village whose name the hill takes on and headed over a roughed field where cattle had marked the ground with gauged hoof prints amongst high summer grasses, this led to a still stream and an opposing grassed bank leading to a gate and a narrow lane in to the hills.

Leaving the lane a track headed east toward what now looked like holiday homes at Upper Caerfaelog, crops swayed in the morning light breeze, delicately being turned this way and that, I stopped beside a gate and luxuriated myself in the colour of green and blue with this delicate movement almost mesmeric.

Blues and greens of summer

Reaching Upper Caerfaelog a rusted tractor stood under a tree, abandoned and now a fixture planted in place and time.

Tractor outside Upper Caerfaelog

The track I was on is just one of many in Radnorshire that lead purposely but gently in to the county’s hills, these are wondrous to find and tell of a time long gone, but still there if necessity calls.

I continued following the track east, only diverging from it to bi-pass a herd of cattle, who inquisitively approached when I was on the their other side, their eyes bright, big and invitingly beautiful, they stood and looked my way, I did likewise, but at them.

The track led toward the critical bwlch adjoined to Cefn Llanbister which is placed off the common land in a forgotten field under a small tree.  As the Trimble slowly ebbed down to its 0.1m accuracy level before data should be logged I sat beside another tree in the sunshine and immersed myself in the wonders of life, where little stirred and no other person knew where I was, this I found a lovely feeling of abandonment, with little outside stress or pressure and where the it and the now were prerequisites to my immediate life.  I spent over 30 minutes in this field as the Trimble took about 20 minutes to attain its accuracy level and I then decided to gather a ten minute data set, and all of this time was one of quality.

Gathering data at the critical bwlch of Cefn Llanbister

Leaving the bwlch I re-joined my inward track which led up toward the continuation of the lane where I had earlier parked.  The lane led toward another track that swung left across the common land making up the summit of this hill.

I had LIDARed this hill the previous day and the ten figure grid reference produced for its summit led me to the hill’s high point, which was on a narrow green path amongst a mass of gorse. 

LIDAR image of Cefn Llanbister

I set the Trimble up and waited for another ten minute data set to be gathered and stored.  A breeze blew lightly during data collection, and I stood, without much care, looking, enjoying, and happy.

Gathering data at the summit of Cefn Llanbister

Once the allotted data were gathered I closed the Trimble down, packed it away and followed the green path to an earthen track back on to the lane, and then down to Llanbister where I stopped and chatted with a couple who were finishing building there new house, ten or so minutes later I walked the few metres to my car and thought what a lovely way to spend a morning, being undisturbed on a hill. 

Survey Result:

Cefn Llanbister

Summit Height:  377.5m (converted to OSGM15) (significant height revision)

Summit Grid Reference:  SO 11690 73303 (summit relocation confirmed)

Bwlch Height:  335.3m (converted to OSGM15)

Bwlch Grid Reference:  SO 12399 74601

Drop:  42.2m

Dominance:  11.17%

For further details please consult the Trimble Survey Spreadsheet