29.08.15
Winllan Hill (SJ 217 214)
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| Winllan Hill (SJ 217 214) |
Having waxed lyrical on
yesterday evening’s walk to Winllan Hill I re-visited its summit this morning
and took a further five data sets as yesterday’s data, when processed, showed
the Estimated Accuracies to be 0.5-1m: 57.49% and the Standard Deviation to be
0.9m. The detail within this data set is
probably the worst the Trimble has produced during the last 21 months. Perhaps the large overhanging tree at the
summit obstructed satellite coverage to a greater degree than I had imagined,
or perhaps it was getting too late and the Trimble just needed to go to bed?
As the afternoon’s
forecast was for heavy localised showers I wanted a relatively early start and
by 9.30am I was back on top of the hill.
On our previous evening’s walk Mark and I had ascended this hill from
the west, this morning I parked in a pull-in spot and walked up the paved road /
track that leads to Plas Onn and approached this hill from the north.
I knew exactly what I
wanted to do and had come well prepared with every available piece of surveying
equipment that I possess. My aim was to
gather a number of data sets and to do so in a variety of ways; this at least
would give a comprehensive comparison between styles and the heights
produced. At the very least this would
give an opportunity for the average of all data sets to be taken as the height
for this hill.
When I arrived at the
summit I stored the majority of gear beside the base of the large overhanging
tree and headed down to where the 216m spot height on current Ordnance Survey
maps appears on the ground. This is
situated at or near to a ringed and grassed natural embankment which resembles
the remains of an earthen embankment that one would usually associate with an
ancient hill fort, but there is no map evidence that one ever existed on this
hill.
Once this point had been
identified I set the Trimble up and as it gathered its five minutes of data I
assembled my old measuring staff. Once
the data set was complete I closed the Trimble down and left it in situ and
proceeded to take a reading at a 4½ ft height level from
the land between where the Trimble was placed and where the high point of the
hill is situated under the large tree.
By aligning the fixed spirit level on my measuring staff with the base
of the Trimble I then turned 180° and took a reading
toward the high point of the hill. Once
re-positioned at this point it meant that this ground was approximately at the
same height as the position of the Trimble, I then took readings to the summit
with the conclusion being that the summit of the hill is approximately 9ft 2″ higher
than where the Trimble was placed, which was at or near to where the 216m spot
height appears on the ground.
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| The 1st of the morning's data sets - gathering data from near to where the 216m spot height appears on the ground |
I then took a second five
minute data set with the Trimble from the same spot, and once complete I
repeated the measurement with my old staff but started from the position of the
Trimble, this meant a greater horizontal distance for the first 4½
ft vertical height measure, by doing this I would have a comparison of
measurements taken with the old staff.
This second measure gave a vertical height gain between the Trimble
position and the summit of approximately 8ft 10″ with the average of the
two measurements with the old staff being 9ft.
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| The 2nd of the morning's data sets - with the Trimble just evident on the top of the grassy mound to the right and the much higher summit of the hill on the left |
I now wanted to try and
get another data set from the high point, whereas the Trimble was set up on top
of my rucksack the previous evening with a 0.43m measurement offset recorded, I
now positioned the Trimble on the improvised Tupperware tripod which elevated
its internal antenna by 0.18m above the ground.
During this data
collection I stood behind the large tree out of view of the Trimble and only
went out into the field to encourage sheep to graze in another part of the
field, as they were slowly encroaching westward toward where the Trimble was
now gathering data.
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| The 3rd of the morning's data sets - with the Trimble at the summit set up on its improvised Tupperware tripod |
Once this third
morning’s data set was complete I switched the equipment off and grabbed my
measuring staff as this time I wanted a data set with the Trimble positioned 4½
ft below the summit of the hill which would probably give it a greater chance
of achieving a good data set. I proceeded
to take readings at a 4½ ft height level until I had aligned the spirit level with
the high point of the hill, I then positioned the Trimble on top of my rucksack
and measured a 0.42m offset.
By now the sky towards
The Wrekin away to the east was breaking out into heavy showers, thankfully
these were forming behind Cefn Digoll (the Long Moutnain) and were pushed
northward into Shropshire, but as I started to sort out the gear for the fifth
and last of the morning’s data sets I noticed a large grey patch of sky forming
in the Dyffryn Meifod and as this was closer to Winllan Hill, I did not want to
linger.
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| To the east showers were breaking out over The Wrekin |
As the Trimble gathered
data positioned 4½ ft below the summit and 0.42m above the ground on top of my
rucksack I assembled the tripod and fixed the external antenna to its top. I haven’t used this tripod for a number of
months, as it is always more convenient to use the Trimble operating with its
internal antenna, but necessity dictated that a variety of surveying methods
would give a comprehensive coverage in determining the height of this hill.
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| The 4th of the morning's data sets - with the Trimble positioned 4½ ft below the summit and on top of my rucksack |
Once the fourth morning’s
data set was completed I assembled the tripod and Trimble over the high point
of the hill and set it to gather data.
The Trimble always looks good when on its tripod and the external
antenna was now positioned above the fence which runs east – west adjacent to
the high point of Winllan Hill. However,
the large tree was overhanging the position of the tripod so it’ll be
interesting to compare this data set with the others.
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| The Trimble connected to its external antenna at the summit of Winllan Hill |
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| The 5th and last of the morning's data sets - with the Trimble attached to its external antenna and positioned on its tripod |
As I closed the Trimble
down after it had stored the last of its data the showers that had started to
appear were still being pushed down into Shropshire away to my east, and
patches of sunshine were now breaking out around me. Once all my gear had been checked and packed
away I retraced my steps back down the hill and headed home.
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| The view south-west from the summit of Winllan Hill |
Survey Result:
Winllan Hill
Summit Height: 220.3m (average of six surveys and converted to OSGM15) (significant height revision)
Summit Grid Reference: SJ 21709 21460 (summit relocation confirmed)
For further details please
consult the Trimble survey spreadsheet click {here}
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