Mapping Mountains – Trimble Surveys – Yr Eifl

03.10.18  Cae Doctor (SH 304 399)  

The summit of Cae Doctor (SH 304 399)

This hill was the last of seven visited during the day with each summit being Trimbled, and as a marginal P30 and its bwlch not LIDARed, the summit and bwlch needed Trimbling. 

The summit of this hill comprises two glazing fields that are separated by an old and high field boundary incorporating a stone wall, gorse hedge and fence.  If time permitted I wanted to take a data set from each side of this boundary, but as the high ground of each field was visually similar, one data set was deemed sufficient if also bwlch data were gathered.

Leaving the car we followed a track that soon brought us to the boundary hedge, and deciding to survey the eastern side Aled walked the periphery of the field boundary and stopped where he judged the natural summit of the hill to be situated, within a couple of metres this matched the grid coordinates produced by LIDAR.

I placed the Trimble on top of a fence post to give it elevation above its immediate surrounds and with the assistance of Aled measured the offset between its internal antenna and the ground below and once the 0.1m accuracy level was attained pressed ‘Log’ and we each then stood either side of the equipment and a few metres away from it.

Gathering data at the summit of Cae Doctor

During data collection two vehicles appeared on the hillside opposite, the higher one belonged to the local gamekeeper, whilst the lower vehicle was dropping feed off for livestock and turned out to be the local farmer, we found this out after the Trimble had gathered its allotted data and was packed away, as when we walked toward the gate giving access to our inward track we were met by the local farmer, who seeing us in the field had driven up the track to find out what two people were doing standing in her field for ten minutes or so about 50 metres apart.  It was time for an explanation.

The Trimble set-up position at the summit of Cae Doctor

The local farmer is Awen Roberts and she proved more than helpful as once the Trimble and its function and our interest in upland place-name research was explained she told us that the field where we had been standing is known as Cae Doctor, and the adjacent field on the other side of the boundary hedge is known as Cae Myllt, and she then gave permission for the other high field to be surveyed.

Having thanked Awen we walked in to the other high field, found its natural high point and again I positioned the Trimble on an adjacent fence post and waited for the allotted data to be gathered and stored.  All that remained was to visit and gather a data set from the bwlch.

Gathering data at the summit of Cae Myllt

The bwlch for this hill lies in a long valley that is steep sided with a public footpath leading us to where contour interpolation places its critical point.  Again the Trimble was placed on top of a fence post to give it elevation and the offset measured, and once the allotted data were gathered we walked back up to the awaiting car and I then drove the short distance to Nefyn. 

Heading toward the bwlch

The first data set in the area of the bwlch

The reason for doing so is that the Ordnance Survey Interactive Coverage Map hosted on the Geograph website gives a 37m spot height at a road junction that could be the position of this hill’s critical bwlch, although we had dismissed this from our on-site visit to the valley as ground beyond where the Trimble had gathered data seemed to descend toward this road junction.  However, being a completest I wanted this last data set as a comparison with the previous one.

The second data set in the area of the bwlch

Once this last data set was stored I joined Aled in the car and drove back to pick his car up.  Once home Aled analysed LIDAR and determined the height and position of this hill’s bwlch, and when coupled with the Trimble summit data the hill retains its P30 status and increases its known drop value, and these values are given below.

  

Survey Result:

Cae Doctor (significant name change)

Summit Height:  67.0m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 30425 39978 (Trimble GeoXH 6000)

Bwlch Height:  35.8m (LIDAR)

Bwlch Grid Reference:  SH 30747 40107 (LIDAR)

Drop:  31.2m (Trimble GeoXH 6000 summit and LIDAR bwlch) (30-99m Sub-Twmpau reclassified to 30-99m Twmpau)

Dominance:  46.59% (Trimble GeoXH 6000 summit and LIDAR bwlch)

For further details please consult the Trimble Survey Spreadsheet