Thursday, 7 March 2019

Mapping Mountains – Trimble Surveys – Mynydd Twr


22.10.18  Pen Mynydd (SH 514 748) and Cae Mawr (SH 506 745)  

Cae Mawr (SH 506 745)

The small community of Penmynydd is the ancestral home of the Tudor’s and as its name implies it is the top of the mountain, this is figuratively speaking as although its upper lands give extensive views, these are of rolling agricultural lands and not ones of dramatic cliffs and crags.

Pen Mynydd was the first of a number of hills I hoped to visit and Trimble during the day as I made a sweep of the south-eastern corner of Ynys Môn.  The hill’s high point is recognised as being its triangulation pillar, or at least land beside it, as it is perched on a high concrete plinth which elevates its height above the ground.

I parked beside the access track leading to the high mast which is positioned adjacent to the field at the immediate south of the trig pillar.  From here it was only a matter of a minute or so in to this field.

As I entered the field the top of the trig hovered above the gorse hedge which makes up a part of the field boundary with the narrow road that heads from Penmynydd toward Rhoscefnhir.  Away to the south-east the higher Eryri peaks were enshrouded by cloud with the first direct light breaking through as a yellowed glow.

Tryfan from Pen Mynydd

I judged the highest natural land to be positioned a few metres from where the trig pillar is positioned, although the field is relatively flat and makes an arc away from this position and back toward the mast.  As a fence post was directly over the point I’d judged to be the highest I placed the Trimble on top of it, measured the offset between its internal antenna and the ground at its base and waited for the allotted data to be gathered and stored.

Gathering data at the summit of Pen Mynydd

During data collection I stood away from the equipment and watched as the sun broke through the cloud and also kept an eye on a small herd of cows that slowly munched their way through the morning’s grass close to the entrance in to the field.

The Trimble set-up position at the summit of Pen Mynydd

Once data were gathered and stored I exited the field and visited the trig, afterward I walked the short distance down the road to Parciau farm and spoke with Huw Roberts, who told me that the field was a part of Tyn Llan land and that Selwyn Hughes should be able to help me with confirming its name.

The Trig pillar at Pen Mynydd

I then drove back down the narrow lane to where it meets the B 5420 and parked just off the road and walked up the B road to an old gate which gives access to a field where the rubbled remains of a quarry are situated.  The high point of this field is at the top of the small quarry and is given an uppermost 105m contour ring on contemporary Ordnance Survey maps, as opposed to the 106m height given to the trig pillar.

I soon had the Trimble positioned on what I judged to be the highest natural rock beside a small mound of rubble and activated it to gather data once another small herd of inquisitive cows had paid their customary visit and a few minutes later ambled off.  As data were collected I sat a few metres away from the equipment content with my morning’s lot whilst bathed in welcome sunshine.

Another small heighted hill and another herd of friendly cows

Gathering data at the summit of Cae Mawr (SH 506 745)

Once the Trimble was packed away I wandered back to my car and drove the short distance to Tyn Llan where I met Selwyn’s daughter; Gwenno.  She had recently moved back to the family farm having lived and farmed near Harllech and she kindly gave me a number of field names for the land positioned around the trig pillar which she knew as the Golygon, which included the name of Top Cae Mawr for the field where I had gathered data from.

Gwenno Pugh

All that remained was a visit to Tom Thomas who farms from Dragon-wen and who was introduced to me by Gwenno as Tom Dragon.  It is Tom’s land where the second top I had just surveyed is positioned.  I met Tom beside the road next to his farm and we sauntered over to the fence adjacent to the field where I had just gathered data at the old quarry,  this field was named Bonc at the time of the Tithe, it is now known as Cae Mawr, and it is as its name implies; a large field.

Thanking Tom for his time I then checked the map for onward directions and headed north-westward toward my next hill.       



Survey Result:



Pen Mynydd 

Summit Height:  106.8m (converted to OSGM15, Trimble GeoXH 6000) (surveyed as higher than Cae Mawr [SH 50676 74554])

Summit Grid Reference:  SH 51454 74800 (Trimble GeoXH 6000)

Bwlch Height:  72.9m (LIDAR)

Bwlch Grid Reference:  SH 52054 76272 (LIDAR)

Drop:  33.9m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  31.76% (Trimble GeoXH 6000 summit and LIDAR bwlch)





Cae Mawr 

Summit Height:  106.8m (converted to OSGM15, Trimble GeoXH 6000) (surveyed as lower than Pen Mynydd [SH 51454 74800])

Summit Grid Reference:  SH 50676 74554 (Trimble GeoXH 6000)

Bwlch Height:  c 97m (interpolation)

Bwlch Grid Reference:  SH 50946 74626 (interpolation)

Drop:  c 10m (Trimble GeoXH 6000 summit and interpolated bwlch)

Dominance:  9.17% (Trimble GeoXH 6000 summit and interpolated bwlch)









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