Mapping Mountains – Trimble Surveys – Cymoedd Gwent

25.08.18  Mynydd Ton (SS 949 940)  

Mynydd Ton has a convoluted history for summit placement as it was originally given to where its 535m map heighted trig pillar is situated; its summit position was then moved to an ancient cairn where a 1,769.3ft (539m) surface height is given on the series of Ordnance Survey Six-Inch maps, this latter position was surveyed using the Trimble GeoXH 6000 in July 2016 as being 534.2m in height, therefore dependent upon the flush bracket accuracy the ground at the base of the trig pillar will be higher, therefore the summit was relocated back to that of the triangulation pillar.  Today we hoped to gather data from ground beside the trig pillar and compare this against the data previously taken from beside the ancient cairn.

As Mark, Aled and I set off up the gravelled track that leaves the road junction between the A4061 and the A4107, the distinctive profile of Corn Du and Pen y Fan were silhouetted against a foreground of sparkling white wind turbines as the terraced rows of houses in Cwmparc stood bolt upright in the valley below.

The distinctive profile of Corn Du and Pen y Fan in the background with the regimented houses of Cwmparc in the valley below

Gaining height on the wide track the roads below meandered around adjacent hillsides, with the mast and wind turbines on Werfa to our west being a distinctive landmark, by now the sun was relatively low in the sky casting delicate and appealing colour on the land.

Meandering roads and wind turbines atop Werfa

Looking out toward Werfa

Leaving the track we followed a path toward the conifer plantation that swamps the eastern part of this hill, adjacent to this the path followed the forest’s perimeter fence toward a wide forest break that heads east toward the summit of the hill.  The last time I was here an abandoned 4x4 vehicle added unfortunate novelty to the scene, thankfully this has now gone but some of its remains are still scattered across the grassland of the wide forest break.

Our first port of call was the trig pillar which is relatively easy to find amongst the trees as an avenue has been cut leading to its secluded grove, and almost Narnia like it nestles in its small clearing where once open hillside would have given extensive views.

Entering the avenue of conifers leading to the secluded grove where the trig pillar is situated

The trig pillar in its secluded grove

We assessed the land at the base of the trig pillar and once the position of the high point was determined I placed the Trimble on top of the trig and took a measurement offset to the summit, we now waited for it to slowly ebb  down toward its 0.1m accuracy level.  A five minute data set was gathered from the summit and we then left through the enclosed avenue of cultivated conifers to the open forest break.

Gathering data at the summit of Mynydd Ton

As data had previously been gathered from beside the ancient cairn we opted for a second data set in the wide forest break close to the perimeter fence, we had assessed this land when heading toward the trig pillar and judged it to be slightly higher than that beside the ancient cairn.  Having walked back on the forest break from close to the trig pillar we also thought this to be close in height to that beside the trig.

Beside the ancient cairn

Therefore as Mark and Aled stood beside the perimeter fence watching the sun slowly sink in the western sky I positioned the Trimble atop its improvised tripod of my rucksack and gathered the last data set of the day.

The Trimble set-up position and the last data set of the day

Once the Trimble was packed away I joined Mark and Aled and stood and admired the scene of setting sun with the view as far as the hills of south-west England rising above the Bristol Channel.

Looking out toward the hill's of south-west England

Watching the sun set behind Werfa

To our west the mast and wind turbines on Werfa gave dimension to the hill and added detail to a scene of delicate colour that slowly unfolded from the oranged hues of a sinking sun to the pinks and mauves when light tranquilly disappears.

A myriad of colour as the sun slowly disappeared behind Werfa

It had been another enjoyable day on the hill in good company with all our bagging needs met, but it had also been a long day as after a quick stop in Brecon for chips it meant a late night for all of us, with Aled heading back to Porthmadog from Caersws where his car was parked, and Mark heading home to Mold after having a quick cup of coffee when we arrived back at my home in Welshpool.   

Survey Result:

Mynydd Ton

Summit Height:  534.4m (converted to OSGM15) (significant height revision)

Summit Grid Reference:  SS 94931 94059 (summit relocation confirmed)

Bwlch Height:  443.1m (converted to OSGM15, previously Trimbled)

Bwlch Grid Reference:  SS 93953 94456

Drop:  91.3m

Dominance:  17.08%

For details on the survey of land beside the ancient cairn on Mynydd Ton

For further details please consult the Trimble Survey Spreadsheet

Mapping Mountains – Summit Relocations – Yr Uchafion and 500m Twmpau

Mynydd Ton (SS 949 940)

There has been a Summit Relocation initiated by a survey with the Trimble GeoXH 6000  to the listings of Yr Uchafion and the 500m Twmpau, with the survey that resulted in this summit relocation being conducted on the 23^rd July 2016 in good, clear and sheltered conditions.

The two lists that this summit relocation affects are:

Yr Uchafion, this is the working title for a list that takes in all hills in Wales at and above 500m in height that have a minimum 15m of drop.  This list is co-authored by Myrddyn Phillips and Aled Williams.

500m Twmpau (thirty welsh metre prominences and upward), with the criteria being all Welsh hills at or above 500m and below 600m in height that have a minimum 30m of drop.  This list is authored by Myrddyn Phillips.


The survey was conducted in the range of hills known as the Y Cymoedd, these are the hills associated with the south Wales valleys.  The hill is situated between Cwm Ogwr Fawr to its west and the Rhondda Fawr valley to its east and is positioned above the towns of Treorci (Treorchy) and Treherbert to its north and Nant-y-moel, Price Town and Ogmore Vale to its south-west.

Access to the hill is relatively easy as a track leaves the A 4061 near to its high point and continues south-eastward to the north-western edge of a large conifer plantation, a path continues south-eastward adjacent to the forest boundary gaining the access point to a wide forest break which is relatively near the summit of this hill.

The name of the hill is Mynydd Ton and prior to the survey with the Trimble GeoXH 6000 the height of the hill was listed as 539m at SS 94796 93958 which is beside an ancient cairn.  This height was based on a 1,769.3ft surface height given on the Ordnance Survey Six-Inch map published in 1885.  The 539m figure was a relatively new addition to this hill’s listed height as its summit position was originally listed as ground beside its map heighted 535m triangulation pillar situated at SS 94931 94058.

The highest ground at the base of and beside the ancient cairn was surveyed with the Trimble GeoXH 6000 as being 534.2m (converted to OSGM15) high.  The processed data gave Estimated Accuracies of 5-15cm: 99.41%, with the Standard Deviation being 0.0m, and the margin of uncertainty given for the height placement of the Trimble was 0.1m.  All of the above signify that the data set was good and accurate to within the parameters of the equipment.

I had previously visited this hill in February 2003 and judged ground approximately one minute walk away from the trig pillar to be slightly higher than ground at the base of the trig pillar, and as the flush bracket adjoined to the trig pillar is given a height of 535.335m in the OS Trig Database it means that ground at its base is approximately 535m high.  This figure is dependent upon the accuracy of the flush bracket height which is given as 3^rd order.   Therefore the ground at the base of or near to the triangulation pillar is likely to be higher than that beside the ancient cairn.

Therefore the position of the relocated summit is at SS 94931 94058 and consists of ground at the base of, or near to the triangulation pillar.  This re-located summit position is at the hill’s originally listed summit and is given a 535m height on current Ordnance Survey maps and it is approximately 175 metres north-eastward from the previously listed summit position.

The full details for the hill are:

Cardinal Hill:  Werfa

Summit Height:  534.4m (converted to OSGM15)

Name:  Mynydd Ton

OS 1:50,000 map:  170

Summit Grid Reference (New Position):  SS 94931 94059 

      

Drop:  91.3m (converted to OSGM15)

The Trimble GeoXH 6000 gathering data beside the ancient cairn on Mynydd Ton, with the relocated position of the summit approximately 175 metres to the north-east and to the right of the forest break in the centre background of this photograph

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

For details on the 2nd survey of this hill

Myrddyn Phillips and Aled Williams (August 2016)

Mapping Mountains – Significant Height Revisions – Yr Uchafion and 500m Twmpau

Mynydd Ton (SS 949 940)

There has been a Significant Height Revision initiated by a survey conducted with the Trimble GeoXH 6000 to a hill listed in the Yr Uchafion and the 500m Twmpau (thirty welsh metre prominences and upward), with the survey that resulted in this height revision being conducted on the 23^rd July 2016.

The criteria for the listings that this height revision affects are:

Yr Uchafion - All Welsh hills at or above 500m in height that have 15m minimum drop.  The list is co-authored by Myrddyn Phillips and Aled Williams

500m Twmpau - All Welsh hills at or above 500m and below 600m in height with 30m minimum drop.  The list is authored by Myrddyn Phillips. 

The name of the hill is Mynydd Ton and it is situated in the Y Cymoedd range of hills in south Wales, and the survey was conducted on a warm and sunny afternoon in good, clear conditions.  The Y Cymoedd are an extensive group of hills and comprise the area of the south Wales valleys.

Mynydd Ton is situated between Cwm Ogwr Fawr to its west and the Rhondda Fawr valley to its east and is positioned above the towns of Treorci (Treorchy) and Treherbert to its north and Nant-y-moel, Price Town and Ogmore Vale to its south-west, and the hill can be easily accessed from a track that leaves the A 4061 near to its high point and continues south-eastward to the north-western edge of a large conifer plantation, a path continues gaining the access point to a wide forest break which is relatively near the summit of the hill.

Prior to the survey with the Trimble GeoXH 6000 the height of the hill was listed as 539m at SS 94796 93958 with this position being beside an ancient cairn.  This height was based on a 1,769.3ft surface height given on the Ordnance Survey Six-Inch map published in 1885.  The 539m height was a relatively new addition to this hill’s listed height as its summit position was originally listed as ground beside its map heighted 535m triangulation pillar situated at SS 94931 94058.

The highest ground at the base of and beside the ancient cairn was surveyed with the Trimble GeoXH 6000 as being 534.2m (converted to OSGM15) high.  This data set gave Estimated Accuracies of 5-15cm: 99.41% and a Standard Deviation of 0.0m with a margin of uncertainty for the height placement of the Trimble of 0.1m.

On my previous visit to this hill in February 2003 I judged ground approximately one minute's walk from the trig pillar to be slightly higher than ground at its base, and as the flush bracket adjoined to the trig pillar is given a height of 535.335m in the OS Trig Database it means that ground at its base is approximately 535m high.  This figure is dependent upon the accuracy of the flush bracket height which is given as 3^rd order.   Therefore the ground at the base of or near to the triangulation pillar is likely to be higher than that beside the ancient cairn; this is dependent upon the accuracy of the flush bracket height and the accuracy of the Trimble GeoXH 6000 survey.

The 534.2m (converted to OSGM15) height produced by the Trimble GeoXH 6000 is 4.8m lower than the previously listed height of 539m, which was based on the 1,769.3ft surface height on the 1885 Ordnance Survey Six-Inch map and therefore comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revision applies to any listed hill whose Ordnance Survey summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble.  As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 map is being prioritised in favour of the 1:50,000 for detailing these revisions.

The summit of this hill is easily identified and consists of ground at or near to the triangulation pillar, and therefore this hill’s new summit height is based on the 535m map height adjoined to the trig pillar, as the 534.2m (converted to OSGM15) result produced by the Trimble GeoXH 6000 for ground beside the ancient cairn at SS 94791 93954 is 4.8m lower than the hill’s previously listed height of 539m which appears as a 1,769.3ft imperial height on the Ordnance Survey Six-Inch map.

The full details for the hill are:

Cardinal Hill:  Werfa

Summit Height (New Height):  534.4m (converted to OSGM15)

Name:  Mynydd Ton

OS 1:50,000 map:  170

Summit Grid Reference:  SS 94931 94059 

 

Drop:  91.3m (converted to OSGM15)

The Trimble GeoXH 6000 gathering data beside the ancient cairn at the old summit position of Mynydd Ton which resulted in this hill's significant height revision

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

For details on the second survey of this hill

Myrddyn Phillips and Aled Williams (August 2016)

Mapping Mountains – Trimble Surveys – Y Cymoedd

23.07.16  Mynydd Ton (SS 949 940 [SS 947 939, position Trimbled])    

Mynydd Ton (SS 949 940)

I’d visited Mynydd Ton once before in February 2003 when I followed the track leaving the A 4061 toward a forest break that gave relatively easy access toward where the 535m map heighted trig pillar was situated.  On that day I found ground about a minute away from the trig to be slightly higher, happy with my efforts I retraced my inward route back to my car.  Since my visit a number of Ordnance Survey maps have become available online, including the series of old Six-Inch maps and I believe it was Mick Moore who found a 1,769ft (539m) height on one of these maps that is adjoined to an ancient cairn which is approximately 175 metres south-west from where the trig pillar is positioned.  Therefore I wanted to re-visit the hill and the relatively newly discovered map high point.

As I left my car in a large lay-by near to the high point of the A 4061 the sun was out and young children were happily waiting next to an ice cream van as sheep also queued for any odd piece of food thrown their way.

The view north-east from the lay-by

A track leaves this road and heads up toward the forested summit area of Mynydd Ton, as I walked toward it two trail bikes were going through the gate and sped off across the hill’s northern flank, ahead was a car chugging its way up the track.  As I gained height there were other cars parked high on the track with a number of people flying model aircraft, I said my ‘hello’s’ and continued on the track to where it enters the forestry, I then turned right (southward) and followed a path beside the large conifer plantation to where a wide forest break gives access toward the map high point of the hill. 

Seemingly abandoned in the forest break was a four by four vehicle with its front windscreen partly smashed and its front end also badly damaged, I took a few photographs of it and continued down the forest break wanting to see if I could find the trig pillar that I’d previously visited, deciding that I’d had enough tree bashing for the day from my recent visit to Mynydd Ystradffernol, I back-tracked and headed in to another small forest break where the ancient cairn is situated and where the 1,769ft (539m) Six-Inch map heighted summit is positioned.

The abandoned four by four in the forest break

The cairn has been re-modelled and sits atop an ancient mound, past exploration found a central cist although this seems no longer in evidence.  I positioned the Trimble atop my rucksack deciding that the ground immediately beside the base of the cairn was slightly higher than the solid ground in the centre of it, and left it slowly ebbing down to its 0.1m accuracy level before data should be logged.  During this process I stood beside the trees and waited patiently, looking out past the re-modelled cairn and ancient mound to bright sunshine and the opposing conifers as they stared back at me.  I checked the equipment’s downward progress and once the accuracy level was attained I pressed ‘Log’ and retreated to the periphery of the trees and waited for five minutes of data to be collected.

Gathering data beside the ancient cairn on Mynydd Ton

The Trimble set-up position beside the ancient cairn on Mynydd Ton

As I packed the Trimble away I looked back at the mound and cairn and wondered if I would ever re-visit.  I then headed down the hill and visited the connecting bwlch which was just above where I had parked my car.  I’d examined this area via a Google car the previous evening and knew that a stone wall positioned on the south-eastward side of the road would give the Trimble elevation above its immediate surrounds.

Once at the top of the road which constitutes the area of the bwlch I judged the ground at the base of the wall to be the point of the critical bwlch and measured a 1.23m offset between the Trimble’s internal antenna and the ground at its base and set it to gather another five minute data set.  When it had collected its all-important data I walked the few metres down the road to my car and drove a kilometre westward toward my last hill of the day.

Gathering data at the critical bwlch of Mynydd Ton

  

Survey Result:

Mynydd Ton

Summit Height:  534.2m (converted to OSGM15) (significant height revision and summit relocated to its previously listed position; 534.4m at SS 94931 94059)  534.4m (converted to OSGM15, from subsequent Trimble survey)

Summit Grid Reference:  SS 94791 93954 (based on Trimble survey with the summit now relocated to SS 94931 94059)  SS 94931 94059 (from subsequent Trimble survey)

Bwlch Height:  443.1m (converted to OSGM15)

Bwlch Grid Reference:  SS 93953 94456

Drop:  91.1m (based on Trimble survey, 91.3m based on summit relocation and Subhump status confirmed)  91.3m (from subsequent Trimble survey)

Dominance:  17.08%



For details on the second summit survey of Mynydd Ton

For further details please consult the Trimble survey spreadsheet.