Bitstring <[email hidden]>, from the
wonderful person Roger <[email hidden]> said
Quoted message said:The message <[email hidden]>
from GSV Three Minds in a Can <[email hidden]> contains these words:
Quoted message said:I'm trying to check the NASA height survey data against known UK points,
and I've come up with a major error against OS trig point on Brown Knoll
"N53.362989, W001.875700, 236.0,Brown Knoll Mh pil pub s2782 K
Stevens"
Quoted message said:Mh means the height was read from a map (236.0m) .. something must be
wrong since the height data at that lat/lon is ~540m. Does anyone have a
map (or MM, or Tracklogs, or whatever) that they can use to see what is
incorrect .. the position of the trig pillar, or the height given??
Quoted message said:If my OS grid conversion worked right, that's SK08271 85161, more or
less (but I'm sure several of you can find it in the dark in a blizzard
anyway). I'm guessing someone typed a '2' instead of a '5' on the
height, since it makes no sense the trig pillar would not be at the top
of the hill.
Brown Knoll was about there on the 1" with a height of 1866 feet.
Funnily enough that height translates into metres as 568.8 so no change
there. :-)
Even 536m (1759 feet) would be a distant prospect. The nearest the 1750
foot contour comes to the trig point is about 300m.
I guess it was just a complete [censored] then. Anyway, thanks for the
info. NASA believe it is 568m, so I guess the OS got that one right. 8>.
Actually I'm fairly impressed with the NASA SRTM dataset .. apart from
the annoying voids (mostly small) and the odd rogue point (-230m or
whatever) it actually matches pretty well. I've tried all 6495 trig
points I could find position and height data for, and the worst error is
only 80m
(Swinden .. N54.04636 W2.03760 .. anyone know it?) with an average error
of ~5m. Given the NASA data is on 90*45m grid, losing an 80m lump in
there isn't too bad (although it's quite possible that it's the trig
point heights or positions which are wrong). It does have a tendency to
slightly reduce peaks, and fill in valleys, but you'd expect that with a
coarse grid.
Now if I can just find some similar trig pillar position/height info for
Eire and N. Ireland. 8>.
--
GSV Three Minds in a Can
Outgoing Msgs are Turing Tested,and indistinguishable from human typing.
