TrigpointingUK

Hi,

I'm trying to clarify my understanding of the different types of mark for OS ground stations trigs.

Can anyone confirm the following or, alternatively, offer a counter example please.


Thanks
Ted


1. Considering blocks under OSGB36 there are only BLOCKS (implicitly on the surface)
and BURIED BLOCKS. There is no mark type named SURFACE BLOCK in OSGB36.
References to 'Surface Block' in OSGB36 only exist as comments, typically referring to the
conversion of a pillar. Both types of block comprised a metallic object set in concrete (see item 4 below).

2. The mark type of SURFACE BLOCK subsequently appeared for passive stations.

3. OSGB36 Blocks and Buried Blocks were rarely, if ever, adapted as passive station surface blocks.

4. For OSGB36 BLOCK and BURIED BLOCKS the appearance does not critically
determine the mark type. So the metallic object could be a bolt, a rod (usually circular but
sometimes square in cross-section; also threaded or unthreaded) perhaps even resembling a rivet.


Then on to bolts and rivets (again considering only ground stations not roof stations)...

5. OSGB36 marks described as BOLTS were always placed in natural rock

6. OSGB36 marks described as RIVETS were always placed on man-made material,
(for example a kerb stone or drain surround).

Ted,

yes 'Surface Block' is the Passive Station Database equivalent of OSGB36 'Block'; the former option is used because originally only Blocks that were reused as Passives were included in the T:UK database.

I believe that Blocks with large bolts are generally earlier than those with rods/rivets, but have no evidence to hand.

I can think of OS rivets place in natural materials i.e. boulders, but they're all BMs rather than OSGB36 stations.

Hi Bernie,

Thanks for your reply.

Theres an OS page at http://www.ordnancesurvey.co.uk/gps/leg ... n-stations
which is relevant to this discussion. But it is of limited use when trying to understand the difference between
types of mark.

yes 'Surface Block' is the Passive Station Database equivalent of OSGB36 'Block'; the former option is used
because originally only Blocks that were reused as Passives were included in the T:UK database.

I somehow thought the Passive Station surface blocks were all new rather than, in some cases, adaptations of OSGB36 blocks.
Do you have an example of the latter, please.

Pedantically, I think that the term 'Surface Block' should not be used for OSGB36 stations. So for example,
http://trigpointing.uk/trig/14627 should be reclassified in T:UK as a 'Block'.

On the definition of a rivet, a minor improvement would be to say that it is placed on a pre-existing base whereas for a block,
the base was constructed by the OS


Any further feedback would be welcome. I'd like to update the wiki page concerning station and mark types but want to try
and get my throughts (reasonably) correct beforehand.


Regards
Ted (Trig Geek )

Ted,

I entirely agree that 'Block' would be better than 'Surface Block'; both categories were in existence for a short while, and I think the decision to move them all to SB was based on minimum keystrokes at the time. Maybe Ian can relabel the whole lot at once?

For an example of OSGB36 Block re-used as a Passive Station Surface Block see TP0065 Auldhouse just along the road from me. Originally NS77/T404 computed 1954, later recycled as Passive Station C1NS6250.

agentmancuso wrote:
I can think of OS rivets place in natural materials i.e. boulders, but they're all BMs rather than OSGB36 stations.

Druim Breac is a Passive rivet on a natural boulder http://trigpointing.uk/trig/20

and another ... http://trigpointing.uk/trig/111

Thanks Rob and Bernie.

As regards OSGB36 (i.e. pre-passive stations albeit with a small overlap)
I found an example of a rivet in natural rock: http://trigpointing.uk/trig/12963

So much for that theory


Ted