What is a trig?

General discussion about trigpoints, the TrigpointingUK website etc

What is a trig?

Postby Teasel » Mon Jun 02, 2014 12:56 pm

I've been tying myself up in knots about this for years now, and not come to any conclusion. The addition of the final OSGB36 stations makes it the right time to sort this out once and for all! How should we arrange the data in the T:UK database?

The essential definition, as far as T:UK is concerned, is that a trig is something which has a details page, and is what logs are stored against.

So, as things currently stand, although Stanwick Ch Twr has no fewer than nine entries on the OSGB36 database, it is a single loggable trig. This causes two main problems: firstly it makes it difficult to store even the simplest data about trigpoints. Is Stanwick a bolt, a flagstaff or a centre? Should I fundamentally change the site so that each trig has multiple types, multiple locations etc? That would be a lot of work and could lead to much confusion. The second, related problem is what should people log? As it stands, anyone visiting Stanwick is asked to enter a single condition, and gets a single credit for the log. Finding a roof bolt gets no more credit than a drive-by sighting of a flagpole. I suppose I could change the logging screen to prompt for conditions for each of the marks at a station. But that too would mean a fundamental change to the database structure and would potentially be difficult to achieve (especially on a tiny mobile phone screen) without confusing people.

The option of having one trig per record on the OSGB36 database is a non-starter. A visitor to Stanwick should not be presented with nine nearby trigs, six of which are marked as "destroyed" but are actually just earlier surveys of the surviving marks.

A third option would be to create a trig for every mark. ie Stanwick would become three trigs and a visitor to that station would enter up to three separate logs, on three separate trigpoint details pages, depending on what they found. If we went down this route, we could keep most of the existing code for logging etc, although I would want to add a box showing "other trigs in this station" to the trigpoint details page.

So, basically the main options are:
    Option 1 - ~25k trigs, one for each station
    Option 2 - ~33k trigs, one for each OSGB36 / PSD entry
    Option 3 - ~29k trigs, one for each {station, type} combination

The more I think about it, the more I'm coming around to option 3. But then just a few weeks ago, when looking at how to get the remaining OSGB36 stations in, I decided on option 1! Does anyone have any suggestions as to the best way forward?

Cheers,
Ian
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Re: What is a trig?

Postby agentmancuso » Mon Jun 02, 2014 7:37 pm

My opinion on this probably won't come as a surprise to anyone, but I'll restate it anyway, with my reasoning.

I think Option 1 outlined above is best i.e. trig=station, irrespective of number of marks, because:

1) In the OSGB36 dataset, the closest thing to a 'primary key' is the station number. Hence 'trig=station' is closest to OS's own conception of the network.
2) Some users have already expressed the view that non-pillar stations are less worthy than other OSGB36 stations; I fundamentally disagree with this view, but see no purpose in aggravating people further by making an equivalence between trigs and marks that has no basis in OS records.

Going with Option 1 would logically mean merging records where successive pillars of the same station have new FBs; so be it.

Surely now is the time to remove the handful of random benchmarks that still loiter on T:UK?
Likewise, the few Irish pillars listed should also vanish, unless plans are afoot to incorporate the whole Irish network.
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Re: What is a trig?

Postby peregrinus » Tue Jun 03, 2014 6:42 pm

From a practical point of view, option 3. That way we can log the mark (s) we find, when say a church tower has bolt vane and flagstaff. Otherwise if a station is defined by the bolt which isn't accessed, there is no way to log that the vane/flagstaff is present.
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Re: What is a trig?

Postby Teasel » Tue Jun 03, 2014 11:56 pm

Yes, if we are to have a separately loggable trig for each mark, then a prerequisite is to allow people to filter out the trigs they're not interested in from the search results. After that, it would presumably aggravate such people less if the stations were separated out into marks, despite it adding an extra 4k records into the database, as it would make the filtering more effective.

Is it safe to assume that everyone can agree on the same hierarchy of "worthiness"? That way I can allocate a single worthiness to each trigpoint, based on its physical type, then each user can have a single worthiness threshold, beneath which trigs are excluded. Perhaps the following...?

  1. Pillar
  2. FBM
  3. Active, Berntsen, Block, Bolt, etc etc
  4. Intersected Station
  5. User-added trigpoints awaiting admin approval
  6. Controversial trigpoints, eg BMs, Irish, replicas
  7. Deleted trigpoints

(with a default of 3? or 4?)

Or should some of the more substantial (aka "interesting"!) non-pillar marks, such as Curry Stools and Cannon be included in with the FBMs? So we'd have pillars, other substantial structures installed by the OS, marks hammered into pre-existing structures/bedrock, and pre-existing structures used only for intersections. Unless FBMs are to be included in the cull of BMs? (I'm not too happy with that, as I like FBMs and don't want to have to go to another site to log them. But then, I'm biassed!)
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Re: What is a trig?

Postby peregrinus » Wed Jun 04, 2014 5:58 pm

I'd thought in terms of filtering as per the app but your proposal looks sensible. 4 seems the right default for a new user, many will then change theirs to 3.

I too would like to see FBMs stay.
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Re: What is a trig?

Postby agentmancuso » Wed Jun 04, 2014 8:40 pm

Yes, that hierarchy looks sensible to me, and I agree that FBMs are worth keeping (v. precise horizontal positioning, unlike other BMs), and belong with Curry Stools and other sizeable objects.
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Re: What is a trig?

Postby Teasel » Fri Jun 06, 2014 8:04 pm

OK, I've added a rudimentary filter to the website, based on the hiearchy below. Details on the wiki. It's a bit basic right now, and needs a bit of polish. But hopefuly enough to avoid antagonising too many people by the addition of all the new OSGB36 stations / marks.

As for moving from listing stations to marks, I think the sequence should be:
  • Automatically create a new trig for each separate type of mark in a station
  • Add a box to the details page linking to other marks in the station
  • Identify and merge the occasions where the splitting has been over-enthusiastic
The last point is up for debate. For example, marks with type OLD TRIG are sometimes destroyed pillars which were deprecated by building a completely new pillar several metres away, and sometimes they remained and became a bolt. A better case could be made for merging an OLD TRIG with a BOLT into a single trig/mark, than could be made for merging an OLD TRIG with its nearby replacement PILLAR. But the argument that there's no value in creating two records when basically they just moved the pillar a few feet, also holds water.

We can worry about such edge cases later. But the idea is that TrigpointingUK should be a list of OS survey marks; whereas the OSGB spreadsheet is a list of observations, geographically grouped into stations.
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Re: What is a trig?

Postby ted » Sat Jun 07, 2014 11:37 am

I think that, from a bagger's point of view, a single 'tick' should correspond to
a trig station, not to each of its consituent marks. I don't have a strong argument
for this; subjectively it seems the better choice. But if the decision was to log
by mark instead of station I wouldn't be too upset :)

Ideally, it would be useful to distinguish individual mark conditions, so for example
an observation that the flagstaff on a church tower was present, also the remains
of a vane but the roof bolt was not checked. But I feel thats not an essential issue;
its one station in OS terms and should have a single trig record on TPUK.

Pragmatically, converting the database to record marks instead of stations would
create problems, not just for the administrators. Users of the site would need to review
their existing logs, splitting them where necessary and revising individual conditions.
It would be a chore which perhaps many wouldn't bother with. (To a lesser extent this
situation already exists with the separation of 'toppled' and 'moved' conditions - some
logs haven't been revised and give a misleading impression of the trig's condition).

Incidentally, it might be worth annoucing the creation of this Forum on the trigonomy mailing list.
That would probably lead to greater (and more diverse!) feedback on the marks/stations
discussion.


Regards
Ted
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Re: What is a trig?

Postby agentmancuso » Sat Jun 07, 2014 4:59 pm

Teasel wrote:... marks with type OLD TRIG are sometimes destroyed pillars which were deprecated by building a completely new pillar several metres away, and sometimes they remained and became a bolt. A better case could be made for merging an OLD TRIG with a BOLT into a single trig/mark, than could be made for merging an OLD TRIG with its nearby replacement PILLAR...


My understanding is that OLD TRIG refers to an older i.e. pre-OSGB36 survey station whose site was reused and resurveyed. No physical evidence of such earlier stations have been recorded AFAIK, presumably because the station was destroyed in the resurveying process.
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Re: What is a trig?

Postby edfielden » Sun Jun 22, 2014 5:41 pm

My understanding is that OLD TRIG refers to an older i.e. pre-OSGB36 survey station whose site was reused and resurveyed. No physical evidence of such earlier stations have been recorded AFAIK, presumably because the station was destroyed in the resurveying process.


I share this understanding, although in several situations the OLD TRIG can be several metres away from the newer OSGB36 mark(s).

I looked for a few 'OLD TRIGs' during my month in Shetland in Sep/Oct 2012. I saw first-hand at least one of these which I mentioned in my log - http://trigpointing.uk/trig/5957 - as being a small (6-inch square) stone block in the ground with a 'benchmark-arrow' type symbol engraved in the top. Some other OLD TRIG sites had small cairns built on top of them, although I didn't dismantle them to look for any evidence. Some OLD TRIG sites were sort of identifiable by having a slight dip in the ground at the correct spot, although again I did not dig around for evidence.

I'll need to give the question of marks/stations a little bit more consideration before I pick a side, although I will say that personally I would like to be able to log a status for each individual mark at a station... :)
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