Mapping Mountains – Trimble Surveys – Mynydd Hiraethog

18.09.19  Foel Gasyth (SJ 022 622, only bwlch surveyed)

The bwlch of Foel Gasyth is positioned approximately 1km southward from its summit.  The 5m contouring on the OS Maps website and a digitised inspection in a Google car suggested that there are two points that vie for the critical point of this bwlch.  The first is adjacent to B4501 road as it makes its way north-eastward toward the town of Dinbych (Denbigh) and the second is in an adjacent field.  I hoped to survey both.

LIDAR summit image of Foel Gasyth (SJ 022 622)

It was just past midday when I pulled my car up adjacent to a gate close to the high point of this part of the B road.  The conditions remained becalmed with in the main blue sky, although a bank of high milky cloud was pushing in from the north.  Except for a rogue lorry and an occasional vintage car the B road remained quiet, as did the surrounds, which for the purpose of my visit was ideal.

The Trimble set-up position at the first option for the bwlch of Foel Gasyth

After a quick inspection of the lay of the land at this point of the road I repositioned my car aligning its roof with the high point of the road.  And once the Trimble was in place on the car roof I measured the offset between its internal antenna and the ground at its base, clambered on top of the surveying steps, created the file in the equipment and waited for the 0.1m accuracy level to be attained before data should be logged, and once attained press ‘Log’ and walked a short distance away so as not to interfere with satellite reception.  The Trimble happily beeped away gathering its individual datum points whilst I scribbled all necessary detail in my note book, took a few photos and once the allotted data were gathered and stored, clambered back on to the surveying steps and pressed ‘Done’.

Gathering data at the first option for the bwlch of Foel Gasyth

I then repositioned my car around the corner of the near cross roads on the widest part of a minor road and walked back to the gate where I originally parked.  The gate gave easy access in to the adjacent field where map contouring implies that a second option for the critical point of this bwlch is positioned.

The interpolated ten figure grid reference led me toward the area of the bwlch, I then assessed the lay of land and chose the spot for Trimble placement.  During data collection a few sheep inquisitively approached before heading back across the wide expanse of the field.

Gathering data at the bwlch of Foel Gasyth

Again, all remained quiet as the Trimble gathered its allotted data; it was as if the whole land was asleep, in a slumber dulled by the sun.  Once five minutes of data were gathered and stored I closed the Trimble down, packed it away and made my exit from the field back to my awaiting car.  Next stop the bwlch of Moel Yta. 

Survey Result:

Foel Gasyth

Summit Height:  377.6m (LIDAR)

Summit Grid Reference:  SJ 02245 62236 (LIDAR)

Bwlch Height:  282.2m (converted to OSGM15, Trimble GeoXH 6000)

Bwlch Grid Reference:  SJ 02055 61204 (Trimble GeoXH 6000)

Drop:  95.4m (LIDAR summit and Trimble GeoXH 6000 bwlch)

Dominance:  25.26% (LIDAR summit and Trimble GeoXH 6000 bwlch)

  

For further details please consult the Trimble Survey Spreadsheet