Deweys – New Twin Top

Deweys – Carn yr Hyrddod and Lan Ddu Fawr – New Twin Top

Along with Aled Williams I recently visited Carn yr Hyrddod (the northerly hill at SN 790 704) and Lan Ddu Fawr (the southerly hill at SN 787 699), with the northerly hill listed as a Dewey. 

Carn yr Hyrddod (SN 790 704)

As LIDAR gives these summits close in height we wanted to take a spread of data and therefore identified three positions to survey at each summit, with the hope that the Trimble GeoXH 6000 could split these tops.

Lan Ddu Fawr (SN 787 699) from the summit of Carn yr Hyrddod

 

The Trimble and LIDAR results appear below:

 

Carn yr Hyrddod:

Summit 1:  592.660m at SN 79069.4 70421.2

Summit 2:  592.729m at SN 79069.3 70421.8

Summit 3:  592.590m at SN 79068.0 70421.3

 

LIDAR gives:

1m DSM:  593.059m at SN 79067 70424

1m DTM:  592.780m at SN 79069 70424

 

 

Lan Ddu Fawr:

Summit 1:  592.724m at SN 78759.8 69974.5

Summit 2:  592.696m at SN 78762.7 69977.2

Summit 3:  592.662m at SN 78761.6 69977.0

 

LIDAR gives:

1m DSM:  593.010m at SN 78757 69975

1m DTM:  592.809m at SN 78761 69976 and SN 78762 69977

 

Both LIDAR and the Trimble have difficulty separating these summits, with 1m DSM giving Carn yr Hyrddod the higher by 5cm and 1m DTM giving Lan Ddu Fawr the higher by 3cm, with the Trimble even closer with only 5mm in favour of Carn yr Hyrddod.  All of these results are within the margin of uncertainty applicable to each method. 

As previously posted; upon Michael’s death his wife offered me co-authorship of the Dewey list.  Therefore, as these summits cannot be split they are now listed as a twin top in the Deweys. 

 

Myrddyn Phillips (May 2025)