Mapping Mountains – Trimble Surveys – Elenydd

 

22.10.20  Fron Ddu (SN 703 775) 

Fron Ddu (SN 703 775)

Having just visited and surveyed the summit of Castell Faen Grach (SN 726 775) it was only a short drive westward toward the next hill of the day; Fron Ddu.  This was the second of seven hills I hoped to visit during the day and all form a part of the land that extends westward from the parent hill of Pen y Garn to the coast and that has the Afon Rheidol bordering in the north and the Afon Ystwyth in the south.  The land above the Afon Rheidol is steep sided with the stream having created a small gorge with wooded sides immediately above, and this was on show as I drove the short distance to a lay-by from which I could have an easy ascent of Fron Ddu. 

Prior to visiting I had analysed this hill’s numerical data via LIDAR and this gives the summit position beside the triangulation pillar that adorns the high point of the hill.  LIDAR gives the summit height as 339.0m, which is over 0.8m lower than the 339.827m flush bracket height on the trig pillar; therefore I was expecting the trig to be placed on a plinth. 

LIDAR image of Fron Ddu

Many of the hills that I visited during the day are no more than high fields given over as pasture for sheep grazing, and because of this their profiles blend in to the landscape, merged with many other similar fields.  However, the trig pillar atop Fron Ddu distinguished it from a distance and especially so from the slopes of Pengegws (SN 702 755) which was my fourth hill of the day.  From here the trig could just be made out poking above the high point of the upper field of the hill and I spent a few minutes waiting for a flash of light to highlight a part of the hill framing it with Llyn Rhosrydd in the foreground. 

Having parked my car it was only a short distance back on the road to the bridleway that heads west on the northern flank of this hill.  I followed this through a gate with the bridleway now no more than a grassed vehicle track. 

The bridleway on the northern flank of the hill

Leaving the bridleway I made my way up a field toward a fence, it was good to be out on the hill wrapped up in my autumnal fleece, although I still braved wearing shorts for the day.  The higher tops to the south-east and east were bathed in morning clag with a stream of whitened grey cloud stretching across the sky, thankfully the hills I had chosen for the day were all under the cloud base with Pen Felin Wynt (SN 725 759) that has a map height of 372m, being the highest. 

Once over the fence the trig pillar was only a short distance away, and it was indeed positioned on a plinth which accentuated its height.  It was an easy task to assess the lay of land beside the trig and once I’d chosen the spot for Trimble placement I set it up atop my rucksack, which is used as an improvised tripod, measured the offset between its internal antenna and the ground at its base, waited for the 0.1m accuracy level to be attained before data should be logged and then stood back as the allotted data were gathered and stored. 

Gathering data at the summit of Fron Ddu

During data collection I scanned the land, picking out the hills I would visit later in the day.  As the equipment was placed close to the trig pillar I left it gather data for eight minutes, and then closed it down and packed it away. 

It was only a short distance to the bridleway and before heading back to the car I called at Penbwlch Crwys to make place-name enquiries, and although I had a lovely conversation with the young woman who answered the door, she could not help me with either a name for the hill or the upper field where the summit is situated.  Thanking her for her time I waved by goodbyes and sauntered the short distance on the road back to my awaiting car. 

 

Survey Result: 

 

Fron Ddu  

Summit Height:  339.1m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SN 70380 77561 (Trimble GeoXH 6000) 

Bwlch Height:  289.0m (LIDAR)

Bwlch Grid Reference:  SN 70757 76542 (LIDAR)

Drop:  50.0m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  14.75% (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

 

For further details please  consult the Trimble Survey Spreadsheet