Mapping Mountains – Trimble Surveys – Cefn yr Ystrad

06.06.23  Cefn y Brithdir (SO 120 043) 

LIDAR image of Cefn y Brithdir (SO 120 043)

I’m not sure what to say about this hill as we parked about 100 metres from its summit.

Cefn y Brithdir was my third Pedwar of the day and Mark’s fourth.  A minor road follows the course of its broad ridge, which is aligned north-west to south-east.  Prior to our visit I had read reports that the mountain road had recently been closed via a swing gate, which on recent visits by a number of hill baggers was locked, with fly tipping the probable reason for this.  Today, the swing gate was open and therefore we took full advantage and drove up as high as we could, eventually parking on the grass verge beside the minor road having turned around to face our route down which was ever northward.

Once out of the car Mark checked his GPS and declared that it was 83 metres to the top, just my kind of ascent!  I followed him as he strode out to conquer the summit of another Pedwar. 

LIDAR summit image of Cefn y Brithdir (SO 120 043)

Prior to visiting these hills,  I had analysed new Welsh LIDAR and noted the heights and ten figure grid references for each summit and bwlch on our mini bagging bonanza.  LIDAR gives the high point of Cefn y Brithdir about 100 metres from where its recognised summit is positioned.  However, LIDAR only gives this point as 9mm higher than the accepted summit position, with two points at the latter position of equal height and about 4 metres apart. 

Happy in the knowledge of having just conquered another Pedwar!

Once at the LIDAR summit we thought a point beside two upright telegraph poles to be slightly higher, therefore as Mark wandered off to the accepted summit position with car keys in hand I set the Trimble up to gather what proved to be the first of three summit data sets. 

Mark on his way to the accepted summit position

Gathering data at the first of three potential summit positions

The second data set was taken at the LIDAR summit position, which was beside or in a large outcrop of reed grass.  At this point Mark was already heading back to the car to laze in the front seat with a bite to eat as the proper business of hill bagging was still taking place, and that of course is the necessity to survey all potential summit positions. 

Gathering data at the second of three potential summit positions 

Once the second data set was taken I strolled over the more attractive accepted summit position which LIDAR gives as 9mm lower, and set about zeroing in to what I judged to be its high point.  This certainly looked higher and was by far the more attractive summit, although a visual comparison is never the best. 

Gathering data at the third of three potential summit positions

Once the third summit data set was taken I packed the equipment away and sauntered down the 100 metres or so back to the car and the patiently waiting Mark. 

 

Survey Result:

 

Cefn y Brithdir                          

Summit Height:  444.8m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SO 12037 04322 (Trimble GeoXH 6000)

Bwlch Height:  358.2m (LIDAR)

Bwlch Grid Reference:  SO 10819 06005 (LIDAR)

Drop:  86.5m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  19.46% (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

 

For further details please consult the Trimble Survey Spreadsheet