Trig Point Elevation

[SqueakyBoots]

Can anyone tell me at which point the on a pillar trig point the elevation is referenced? Is it at the top of the pillar where the theodolite is attached or at the benchmark plate, or somewhere completely different?

[ted]

Can anyone tell me at which point the on a pillar trig point the elevation is referenced? Is it at the top of the pillar where the theodolite is attached or at the benchmark plate, or somewhere completely different?

My informal understanding is that the reference is to the top of the arrow on the Flush Bracket (benchplate).

http://www.ordnancesurvey.co.uk/gps/leg ... n-stations states
Flush Brackets "This is the point to where, if levelling has taken place, the height above the datum will be referred."
but then somewhat confusingly, goes on to say
"Shows the height above Ordnance Datum in metres, referred either to the flush bracket or the top of the pillar."
I would assume that the top of the pillar is only used as a reference in the (exceptional) cases where a pillar never
had a bracket.


Regards
Ted

[peregrinus]

http://www.ordnancesurvey.co.uk/gps/leg ... n-stations states
Flush Brackets "This is the point to where, if levelling has taken place, the height above the datum will be referred."
but then somewhat confusingly, goes on to say
"Shows the height above Ordnance Datum in metres, referred either to the flush bracket or the top of the pillar."
I would assume that the top of the pillar is only used as a reference in the (exceptional) cases where a pillar never
had a bracket.

I'm sure I've seen something like "levelled to top of pillar" in the OS comments against some of the pillars which don't have FBs. The OS seemed to go through a brief phase of omitting FBs (and/or in a particular area) then went back to including them.