Mapping Mountains – Trimble Surveys – Stiperstones

 

06.10.25  Corndon (SO 305 969, previously Trimbled) and Lan Fawr (SO 297 967, previously Trimbled) 

Corndon (SO 305 969) on left and Lan Fawr (SO 297 967) on right

The passing of seasons is emphasised amongst the hills, with colour and temperature change.  When the greenness of summer subtly changes to those rusted autumnal colours and summer warmth giving way to chilled temperatures when extra layers of clothing give comfort.

It seemed the summer still lingered as I headed up the narrow road leading to the small community of Priest Weston, with greened grasing fields and iridescent blue sky heralding what would no doubt be a chilled evening ahead.

We had a plan, we being me and Abi.  Abi was soon leaving the mid Wales countryside for a job in inner city Manchester and having not seen one another for awhile we arranged to meet on the hill for a catch up.  As Abi finished work at 5.00pm meeting on a local hill was a necessity and Corndon was ideal, with the added bonus of Lan Fawr being close and on our planned route.  It also gave me an opportunity to start before Abi and gain height at a leisurely pace before the quickness of youth caught me up.

Although the weather bode well for our walk, the forecast gave high cloud to push in from the west as dusk darkened.  Therefore, the forecast stilled that enthusiasm for the prospect of a beautiful sunset.  But that wasn’t the priority, it was just good to be out on the hill with the prospect of seeing Abi and catching up with life and related stuff.

Corndon can be quickly ascended via its broad western flank following a fence line that is unrelenting in steepness.  This was our preferred route and I hoped that setting off at 5.00pm would give me a good 30 minutes start on Abi before she was expected to arrive and follow me up with Jake the dog.

I parked just off the narrow road at the start of the track that heads up to the bwlch between Corndon and Lan Fawr.  I’d used this route on a number of occasions and knew it could be a lung buster, with stops on route during the steep bit advisable. 

Corndon from the track

Walking up the track I peered up toward the fence line leading to the summit of Corndon, it seemed no one else was on the hill.  I always enjoy meeting people on the hill, but solitude gives quietness and time to reflect, both on life and also on surroundings.  There’s a quality to hill walking that is hard to define, it gives time for thought, and as I wandered up the track my mind did likewise, not concentrating on any particular thing but opening up to the beauty and simple things close by.  For me this on many occasions can be the radiance of colour, and late afternoon sunlight at this time of year can give a wealth of beauty, from enhanced greens and blues to those subtle grey hues as wisps of cloud gently enhance a deepening colored sky. 

Lan Fawr

By now I was at the gate leading toward the steep bit.  This consists of three sections; the first up open hill to the corner of woodland.  The second section is beside the forestry and the last is beyond the trees to the summit.  Reaching the end of each gives a point to aim for and that all wanted rest.  It also gave time to look back down to the rack and try and spot any sign of Abi and Jake the dog. 

The gate leading to the steep bit

As I neared the summit wisps of cloud slowly danced above the elongated landmass of Cefn Digoll.  Their colour delighted.  To the west the giants of Cadair Idris, the Aran and Berwyn were obscured by murk, so no dramatic sunset was going to be savoured, but as the sun disappeared behind high cloud tinges of golds interspersed amongst the customary whites and greys gave an appealing scene.

The view down the steep bit

 

Wisps of cloud above Cefn Digoll

By now a small figure had appeared beside the fence making their way up in my direction.  The next time I stopped and looked down I spotted they had a dog with them.  It was Abi, and our timing was perfect, as when I reached the trig point on the summit I just had enough time to put my fleece coat on, take a photo of the cairn and trig and make my way back to the top of the fence and there they were; Jake happily leading Abi up the last section toward the summit of Corndon. 

The summit of Corndon

Abi and Jake nearing the summit

It was good to see Abi and especially so on a hill.  One quick hug and lots of catch up and we were soon debating what path to follow for the descent.  Abi suggested the path leading south-eastward toward an ancient cairn that we could see off into the gathering dusk.  From the summit I usually follow a fence that at one time indicated the perimeter of the forestry that for many years obstructed the summit view.  Thankfully this section of forest has now been felled, this route led steeply down to the top of the track opposite the bulk of Lan Fawr, Abi’s suggested route arrived at the same spot, but was much gentler on the knees and proved ideal.  It also gave opportunity to remain high on the hill for another five to ten minutes.  By the time we accessed our onward route through a gate the sun had disappeared and the calming beauty of dusk quickly took the land. 

The last lingering sunlight

The route beyond the gate followed a wide green path leading us down to the continuation of our incoming track.  On our way we chatted about all manner of things.  Arriving at the track the gate leading to Lan Fawr was locked, which it has been on all my previous visits.  Abi decided to take Jake further down the track to find an easier way for him to cross, leaving me to clamber over the gate and slowly head up Lan Fawr. 

Moon rise

My walks usually take place in the morning, gaining height before the heat of the day.  Therefore, I am seldom on the hill at dusk.  However, being here at this moment was both novel and immensely rewarding, with the darkening silhouette of Lan Fawr ahead and glimmers of lights off in the distance my only companions.  It all felt rather mesmerising.

Nearing the top two friendly faces suddenly appeared looking back down on me.  Abi and Jake had beaten me to the summit having found where the perimeter fence ends giving them a direct route to the top.  We only lingered for a few minutes before reversing our inward routes, Abi came partly down the hill toward the gate before vanishing with Jake into the darkness heading back to the end of the fence, whilst I continued and waited for her on the track beside the gate.  Soon I heard the quiet rhythmic sound of gathering footsteps on the graveled track; these soon neared and out of the darkened dusk Abi and Jake reappeared.

All that remained was a contented walk back down the track to our awaiting cars.  Our eyes had by now become adjusted to the dark and although we had torches the descent on the track was ideal at this time of day, reaching my car at 7.40pm, saying bi bi to Abi and waving her off in to the darkness. 

 

Survey Result: 

 

Corndon  

Summit Height:  513.6m (converted to OSGM15, average of two previous Trimble GeoXH 6000 surveys)

Summit Grid Reference:  SO 30599 96922 (from previous Trimble GeoXH 6000 survey)

Bwlch Height:  310.5m (converted to OSGM15, from previous Trimble GeoXH 6000 survey)

Bwlch Grid Reference:  SO 32519 99517 (from previous Trimble GeoXH 6000 survey)

Drop:  203.0m

Dominance:  39.54%

 

 

Lan Fawr  

Summit Height:  426.1m (converted to OSGM15, from previous Trimble GeoXH 6000 survey)

Summit Grid Reference:  SO 29711 96759 (from previous Trimble GeoXH 6000 survey) 

Bwlch Height:  392.6m (LIDAR)

Bwlch Grid Reference:  SO 29966 96784 (LIDAR)

Drop:  33.5m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  7.86% (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

 

For details on the bwlch survey of Corndon

 

For details on the 1^st summit survey of Corndon and the survey of Lan Fawr

 

For details on the 2^nd visit to Lan Fawr

 

For details on the 2^nd summit survey of Corndon and the 3^rd visit to Lan Fawr

 

For further details please consult the Trimble Survey Spreadsheet

Mapping Mountains – Trimble Surveys – Carn yr Hyrddod

 

05.04.25  Lan Ddu Fawr (SN 787 699) and Carn yr Hyrddod (SN 790 704) 

Lan Ddu Fawr (SN 787 699) from the summit of Carn yr Hyrddod (SN 790 704)

Due to independent surveying and LIDAR analysis there are few important hill surveys that remain.  Lan Ddu Fawr and Carn yr Hyrddod are two of these hills.  They are placed in the open grasslands of the Elenydd, approximately 0.5km apart.  Both are topped by the remains of ancient cairns, with scattered rock at their summits.

Considering the wild surrounds of each hill, they are relatively easy to access, with the minor road leading toward the Llynnau Teifi to their south.  The paved section of this road turns to track and continues to Claerwen; one of the remotest farms in Wales.  The track continues from this farm around the northern section of the Claerwen Reservoir, before turning back to a paved road and its continuation east toward Rhayader Gwy. 

The Llynnau Teifi

Lan Ddu Fawr is given a 593m spot height on contemporary Ordnance Survey maps with a triangulation pillar perched in the remains of the ancient cairn which is now fashioned as a wind shelter.  With the flush bracket adjoined to the trig pillar recorded as 592.836m in height.  Whilst, Carn yr Hyrddod is given a 594m summit spot height, which is coloured beige on contemporary Ordnance Survey maps, this indicates an air height, the accuracy of which is not as good compared to that of the flush bracket height.

As current maps give Carn yr Hyrddod 1m higher, it is this hill that is prioritised for listing purposes.  Its classification can be viewed as important as it is listed as a Marilyn, Dewey, Dodd, a Welsh Highland P15 and a 500m Twmpau.  Confusingly the hill originally appeared in the Marilyn and Dewey listings as Waun Claerddu, which applies to land incorporating a large bog to the south-east of the summit of Lan Ddu Fawr.  To add confusion upon confusion the Marilyn list has recently changed its listed name to Lan Ddu Fawr, which applies to the lower map heighted hill and not the higher. 

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

These hills had been on our surveying radar for over a year as the higher map heighted hill is one of our named hills for our Groups within our Regions and Sub Regions.  Whilst, the lower hill is also close to Welsh Highland P15 status with LIDAR giving it 14.6m of drop.  Therefore, our plan was to survey each summit, gathering at least two - three data sets from different positions and also to survey the connecting bwlch between the hills.  The weather forecast for the day’s adventure gave clear blue skies, albeit with a brisk chilling easterly wind.

I met Aled at Dinas Mawddwy at 7.30am and proceeded to drive toward Aberystwyth and then the roads heading south before connecting with the narrow road leading to Llynnau Teifi.  We parked close to a cattle grid and fence that headed up toward our hills.  As I opened the car door, the wind hit me and I quickly changed from shorts to walking trousers.  Thankfully Aled had brought spare gloves which I needed as I had dispensed with my winter gear in favour of a thin pair that would only protect from a slight chill, and that easterly wind definitely needed extra protection as it was chilling to the bone.

From where we parked there are two options for a relatively easy route toward the first of our hills; Lan Ddu Fawr.  One is a wide shaly track rising steeply above the road; the other is a comfortably gradiented green vehicle track that headed up beyond the cattle grid and would in time follow the course of a fence.  I was in following Aled mode and he soon headed up the steep shaly section.  Beyond was open hillside and miles of it in every direction.  This is one of the appeals of the Elenydd and few places in Wales can compare. 

Heading to the hill

Our route soon joined the remains of a leet that contoured around grassed hummocks to our west.  Aled soon left me to bag a P10 sub.  He had a number of these on his planned route, which would leave me on the summit of Carn yr Hyrddod and take a circuitous route across the grass and bog toward Bryn Dafydd, before heading back to Trawsallt and continuing to Disgwylfa and eventually more sub hills before reaching the relative comfort of the paved road below.  This would leave me to survey the summits of Carn yr Hyrddod and Lan Ddu Fawr, via the connecting bwlch, surveying all necessary points on the way, before heading back on our inward route to meet Aled back at the car. 

Lan Ddu Fawr above Waun Claerddu

Aled soon bagged the P10 sub and rejoined me as the leet headed toward a forlorn looking gate.  Here we rested whilst I set the Trimble up on a gate post to attune it with satellite configuration.  From here we contoured around the upper part of Waun Claerddu before heading up the steep southerly slopes of Lan Ddu Fawr, which took us to its summit.  By now we were exposed to the wind and it whisked across the hill, so much so that unless hunkered down behind the wind shelter it proved difficult to communicate.  We spent ten minutes or so assessing the summit area and judging what points needed to be surveyed.  Having picked three candidates we headed off following a sheep track on the moor down toward the connecting bwlch. 

Leaving the summit of Lan Ddu Fawr and heading toward Carn yr Hyrddod

If not for the ten figure grid reference produced by LIDAR it would be difficult to pinpoint where the critical point of this bwlch lay, as it consists of much bog, which today was thankfully almost bone dry.  Writing this post on the 6^th April follows the driest month of March ever recorded in Wales and England, and the first few days of April have been the same.  This helped us during the walk as few places were boggy and that included the bwlch we were now walking through.  Remembering the LIDAR lay-out of this bwlch, Aled pointed toward its critical point as we headed through its stunningly wild surrounds toward the steepening slopes of Carn yr Hyrddod. 

The bwlch between the two hills

As we crested the upper ridge the wind hit us again.  At least the confines of the bwlch had given some respite from its chilled extremes.  This summit consists of a relatively modern cairn and beside it the jumbled remains of the ancient cairn.  We again assessed the lay of land and pinpointed three positions to survey.  At each summit we looked for large rocks that could be deemed as being part of the natural hill.  There is plenty of rock at each summit, but none that could be described as large enough to be a part of the natural hill and therefore surveys were taken to either grass or the ground at the base of the rock. 

Aled at the summit of Carn yr Hyrddod

As we made our way to the summit a figure appeared beside the wind shelter on Lan Ddu Fawr, by the time our summit assessment was complete he had joined us.  Kevin Nicholls had driven up from Cardiff and was part of the SOTA – Summits on the air community, and planned on setting up his gear back on the summit of Lan Ddu Fawr.  He then headed back toward this summit, and soon afterward Aled was off on his wild hill bagging trek.   I watched as he headed down toward a near bog before claiming height on a ridge leading toward the summit of Bryn Dafydd. 

Aled heads off in to the wilds of the Elenydd 

This left me to my surveying activities.  I knew what needed to be done and even though the wind was proving fierce I had faced similar conditions on a few hills before.  However, with six planned surveys on the two summits I knew that the wind would hinder me more so than the Trimble, as even writing the notes in my surveying notebook proved cumbersome and especially so when the wind was blowing my camera strap and Trimble bag back over my head! 

I soon found a suitable rock to place above the first point to survey and positioned the Trimble on top of it, wedging it in place with two smaller rocks.  This proved an ideal solution to the wind and would be employed on the remaining summit surveys.  Having taken a measurement offset from the equipment’s internal antenna to the ground at its base, I waited patiently for the 0.1m accuracy level to be attained before data should be logged, and once achieved I activated it to gather data. 

Gathering data at the summit of Carn yr Hyrddod

During data collection I stood a safe distance away from the equipment so as not to hinder satellite reception, scribbled all necessary detail in my survey notebook, whose pages were flapping about in the wind.  Once five minutes of data were collected and stored I turned the equipment off, took a series of photographs and repeated the process at two further points.  Progress was being made.

Leaving the summit of Carn yr Hyrddod I headed back down to the sheltered confines of the connecting bwlch.  Using the Trimble as a hand-held device I zeroed in to the ten figure grid reference produced by LIDAR analysis.  The DTM and DSM model give the critical bwlch approximately 5 metres apart.  I favoured using the DTM model as the critical point, and this led me to a small channel amongst copious amounts of rather beautifully coloured grass tussocks. 

Gathering data at the connecting bwlch between the two hills

Wanting a rest from the buffeting wind I decided to take two data sets, both from the same position, with the Trimble placed on top of my rucksack, with its base firmly wedged in the bottom of the channel.  After the first data set was complete I re-positioned the rucksack over the same point but with the Trimble now facing a different direction and set it to gather another five minute data set, during which I sat and looked at some extraordinary purple coloured bog enjoying lichen encrusted bulbous beauty that covered the edge of a near peat hag.  This and looking up toward the summit of Carn yr Hyrddod occupied the next few minutes.  Sometimes surveying can take you to some out of the way places, that in their own right are extraordinarily peaceful and have a tranquility all their own, and this connecting bwlch was one of those places.

Once the second bwlch survey was complete I packed the equipment away and headed around any bog and joined the ridge leading to the summit of Lan Ddu Fawr.  Nearing the top I looked east toward the ridge connecting with Trawsallt and spotted a small figure heading toward its summit.  It was Aled.  He had made good progress and I thought that he’d probably get back to the car before me as I still had three data sets to gather atop Lan Ddu Fawr. 

Aled on his way to Trawsallt

When I arrived back at the wind shelter Kevin Nicholls was hunkered down with his aerials already set up and transmitting, talking to friends in various parts of the country.  I said hi and explained that I wanted to take a series of data sets and would be doing so on the far side of the wind shelter for around 25 minutes.  He indicated that he would remain where he was whilst I did my stuff. 

Kevin Nicholls hunkered own with his SOTA equipment in place

I soon had the first position set up, again using a rock to place the Trimble on and two others to wedge it in place.  Once the measurement offset was taken I retreated as it collected another data set.  Once complete I headed back around the cairn to tell Kevin that the first was now complete and two more were to be taken.

This routine of using a rock to slightly elevate the Trimble and give it a solid platform and to protect it from any wind disturbance with two wedged rocks, proved ideal and soon the second data set was complete.  Before moving the Trimble to the last position I again headed off to tell Kevin that only one remained to take. 

Carn yr Hyrddod from Lan Ddu Fawr

The third position was going to be the most difficult to get a good data set from as Aled and I had decided that one needed to be taken at the entrance to the wind shelter.  This meant that even with its slight elevation on its rock the Trimble was faced with higher rock immediately above on three sides.  This is not conducive to either attaining the 0.1m accuracy level before data should be logged, let alone attaining a good data set, we will have to wait and see what the processed data gives. 

Gathering data at the summit of Lan Ddu Fawr

As the last data set was nearing completion Kevin was packing up his gear and therefore a quick bit of wind driven conversation later and we decided to head down the hill together.  All that remained was to take a few photos of the last of the eight survey positions taken during the day, pack the equipment away, get my rucksack on and join Kevin as we headed down the hill.

Our route took us back to the gate where on the ascent I had taken a data set to attune the Trimble to the local satellite reception.  From here we opted to follow Kevin’s inward route, walking on a good quad bike track beside the fence line.  We took our time on our outward walk with lots of good conversation. 

Kevin Nicholls

By the time we arrived back at the two awaiting cars, Aled was already there, flat on his back resting in the sun.  He’d made good time on his route around the hills.  Before leaving we chatted with Kevin for quite sometime about the various hills he’d transmitted from and those he hoped to visit.  It had been an excellent day on the hill, with all plans fulfilled.  It should be an interesting survey result! 

 

Postscript: 

The processed Trimble result could not split the heghts of these hills and therefore they are now listed as a twin top in the Deweys and 500m Twmpau lists.  However, for convenience the data given below uses Carn yr Hyrddod as the prioritised hill.  Please click here for more information relating to the Dewey twin top announcement. 

 

Survey Result: 

 

Lan Ddu Fawr (significant name change for the Deweys)

Summit Height:  592.7m (converted to OSGM15) (summit relocation based on twin top for the Deweys) (summit relocation based on twin top for the 500m Twmpau)

Summit Grid Reference:  SN 78759 69974

Bwlch Height:  578.1m (converted to OSGM15, average of two surveys)

Bwlch Grid Reference:  SN 78931 70288

Drop:  14.6m

Dominance:  2.47%

 

 

Carn yr Hyrddod (significant name change for the Deweys)

Summit Height:  592.7m (converted to OSGM15, Trimble GeoXH 6000) (summit relocation based on twin top for the Deweys) (summit relocation based on twin top for the 500m Twmpau)

Summit Grid Reference:  SN 79069 70421 (Trimble GeoXH 6000)

Bwlch Height:  424.8m (LIDAR)

Bwlch Grid Reference:  SN 79547 66955 (LIDAR)

Drop:  168.0m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  28.34% (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

 

For further details please consult the Trimble Survey Spreadsheet

Mapping Mountains – Trimble Surveys – Drygarn Fawr

16.09.23  Mynydd Trawsnant (SN 824 485) 

The summit area of Mynydd Trawsnant (SN 824 485)

Mynydd Trawsnant appears in a number of hill lists, including the Welsh Highlands – Uchafion Cymru, the Deweys and the 500m Twmpau.  Its summit position in these lists has recently been relocated due to LIDAR analysis conducted by Aled Williams. 

LIDAR summit image of Mynydd Trawsnant

Mynydd Trawsnant is one of many hills is this area that have been swamped by conifer plantation which forms a part of the extensive Tywi Forest.  However, recent visits to its relocated summit reported the forestry in this section felled with newly planted trees already in situ.  Because of this it was an ideal time to visit and gather Trimble data to compare to that of LIDAR.

I had visited its previously listed summit position once before when the barrier at the start of the forest track leading toward its summit was open, not wanting to pass on this invitation I drove up the track and parked close to its then recognised high point.  Before visiting the summit I heard the approaching sound of a forestry lorry and therefore quickly hid behind a tree.  Logging was in progress and not wanting to linger I quickly scampered up the forest ride to what was then considered its high point and just as quickly scampered back down before driving down the forest track to the minor paved road at its end.

Today, along with Aled, we wanted to gather data from the LIDAR high point.  Ideally another data set should be gathered from the old summit position, but again recent visits indicated this was still submerged in conifers.

It’s a long drive south close the eastern shore of Llyn Brianne to where the forest track heads up toward the summit of Mynydd Trawsnant.  Approaching the track we saw that the barrier was open giving access up the hill.  Driving toward the hill we had seen a number of notices relating to a race that was taking place and the arrows indicating the way ahead for the runners pointed up the same track, we wondered whether the barrier was open to give access to the runners and any support vehicles following the race. 

Parked and ready to tackle the relocated summit of Mynydd Trawsnant

Having driven up the track we parked as close to the summit as we could and set off walking at 8.55am as the first flecks of forecast rain began to push northward.  This would herald damp and misty conditions for the continuation of the walk Aled had planned.  However, for me I only had one summit to visit and this was ever so close to where we had parked. 

Setting off up the forest ride between the mature conifers and old summit position on the left and the felled forestry and new summit position on the right

A forest ride between the felled section and the remaining mature tees gave good access and relatively easy underfoot conditions over and close to the old summit position toward the slightly higher LIDAR summit which was ahead of us and to our right.  This as with many felled forested ground looked like an assault course, but thankfully none of it was difficult, although I did manage to almost sit in a water course as I slipped and fell. 

Typical felled forestry land made even more bleak by the grey overhead conditions and incoming rain

The Trimble was used as a hand-help GPS unit to zero in to the co-ordinates ascertained from LIDAR analysis.  When there we debated where the survey equipment should be set up and opted to align it with a patch of grass that was solid and stable.  As the Trimble collected data I sat on a tree stump and scribbled all necessary detail in my survey note book. 

Gathering data at the summit area of Mynydd Trawsnant

Once the equipment was packed away we reversed our inward route, but this time avoiding the water course and aiming for the corner of forest as it butts up against the open hill to its north.  This gave a semblance of what these hills were like before the infestation of conifers.  The open hillside was expansive, albeit with the customary thick and rough Elenydd summer grassland in evidence. 

Heading back to the forest track

Once back at the car I waved Aled off, who was continuing south wanting to visit two subs in the forest before breaking out of the conifers to visit Garn Wen, which is listed as a Dewey and lastly a Pedwar overlooking Llanwrtyd, where we had arranged for me to pick him up in the early afternoon. 

Aled heading off farther in to the forest for what proved a wet and misty few hours

I then set off driving back down the forest track, stopping once to speak with a man who was standing outside his vehicle setting up a small food and drink station for the runners in the race.  He told me there were 21 runners, although the number was originally higher with a number having recently pulled out.

Once out of the forest and back on the minor paved road close to Llyn Brianne I stopped and changed as the rain fell.  It looked a particularly murky scene with grey predominating with mist enclosing many near summits.  It took 55 minutes to drive from here to Llanwrtyd, stopping once to chat with a farmer.

Once at Llanwrtyd I found the car park we had arranged to meet at, read a book, sheltered from the rain and once this stopped walked in to town to find that Caffi Sosban served an all-day breakfast, which once Aled had completed his walk we visited and ate.  An excellent way to end a walk!      

 

Survey Result:

 

Mynydd Trawsnant                   

Summit Height:  516.6m (LIDAR)

Summit Grid Reference:  SN 82452 48564 (LIDAR) (summit relocation –Deweys) (summit relocation – 500m Twmpau and Welsh Highlands – Uchafion Cymru)

Bwlch Height:  378.3m (LIDAR)

Bwlch Grid Reference:  SN 82781 50423 (LIDAR)

Drop:  138.3m (LIDAR)

Dominance:  26.77% (LIDAR)

 

 

For further details please consult the Trimble Survey Spreadsheet