CF 2021 Bearing adjustment source

[Ian Gillespie]

Does anyone else find this annoying: (from the LINZ CS Guidelines)


"The source used for adoptions should be the CSD that measured or calculated the information being adopted, rather than a CSD that merely adopted it from a previous CSD (r 75(2)). For instance, if a vector was measured on DP 1 and then adopted on DP 400000 the adoption on LT 600000 should be from DP 1. The same applies if a bearing correction of 1 min was applied to DP 1 by DP 400000. LT 600000 should show the source as DP 1 with a 1 min bearing correction."


I find it particularly annoying in two instances:


The second is where two different surveys have applied different corrections to an older survey at different locations. Instead of having to apply different corrections, list one of the corrections on the CSD and explain it all in the survey report isn’t it a lot simpler to show the source as the most recent plan showing that line?


The first is on non-primary parcel surveys with little or no survey information. Really, I don’t think we should re-apply bearing corrections to these sorts of plans. The bearings should be from the latest survey that defines lot boundaries.

[Brent George]

I understand that this is one of the things that the SG and plan examiners are now focusing on - after a period of variable interpretations.
(In other words - there will already be plenty of approved datasets with source bearings reported from the most recent plan etc.)

But there is also another problem with the bearing correction part - although not common:-
I have had at least two plans over the last 10 years where I reported a variable correction to one plan.  These were over large rural datasets where we re-observed series of the underlying traverses across the extent of the plan and came up with two different 'corrections'  over different sections of the plan.  I considered that as the old traverse had a good closure (and not a large dispersed Bowditch adjustment), and also that my work was solid, a variable bearing adjustment was justified.  It took some explaining in the report, but was accepted. 
The only issue was deciding which single bearing correction to report in Landonline (I think I chose the correction most used).

 

[Alex Liggett]

I don't find it annoying, but it's the way I was taught from early on, and I'm often skeptical of the methodology surveyors use to determine bearing corrections (so I frequently end up looking at their reports before deciding whether to run with their determination). For example I recently came across one where a surveyor had applied a 20" correction based on a re-measurement of one 40m long line, to a plan covering most of a suburb.

Ian, I don't quite follow the non-primary parcels example. If a previous surveyor has determined a correction to a plan, and you agree that the correction is justified, what's the problem with applying it?

[Ian Gillespie]

Yes you are right.