I’ve just received my copy of Yloande Hodson’s book “The Ordnance Survey Popular Edition One-Inch maps of England and Wales” from the Charles Close Society, probably the definitive work on the Fourth Edition maps.
A Quick look at the coordinates in the back show that my estimates for the Delamere origin are aout by a little bit. My estimates for the offset from the bottom left of the map were:
3640 and 46291 feet
Yloande states the values as
3690 and 46100
so I’m out by 50 feet East/West and 191 feet North/South
Hopefully these new values will reduce the alignment errors. Though since I’m seeing up to 600 feet N/S I’ve still got a bit of work to do.
I shall be checking my automatic cassini calculations for the corners of the maps against the printed lists to see if I can see any discrepancies that I can correct.
Further notes:
I’ve just run a quick test and my calculations for the bottom left hand corner of map 116 are definitely out!
I get
51?13’54″14959/0?24’40″69606 (-709110,-711380 cassini feet)
and Brian Adams gets
51?13’54″13/0?24’40″72 (-709110,-711380 cassini feet)
Clearly a difference in the Lat/Lng but not in the cassini coords.
Another look at the Y Hodson book I notice that the “Constructional Elements” section p.255 says the unit is a Foot (Ordnance Survey Foot of 01 which it then states as:
1 Foot of 01 = 0.3048007491 international Meter. Previously I was using 0.3048
Plugging this little gem in I now get
51?13’54″13165/0?24’40″72226 (-709110,-711380 cassini feet)
compared against
51?13’54″13000/0?24’40″72000 (-709110,-711380 cassini feet)
Woo Hoo!
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