In reading the NSW DTI revised Survey and Drafting for Mine Survey Plans draft version and recently gazetted Survey and Drafting Directions (NSW Coal & Metalliferous amendments 16/5/2014) there is a continual reference to "Class" of survey. There is also similar references to survey "Class" in the Qld Recognised Standard 10 which may or may not be a coincidence?
Anybody aware of how this reference to survey "Class" has become so incorrectly entrenched in both Qld & NSW mining and drafting legislation as quite frankly the use of "Class" does not serve the intent and/or purpose of the documents. Was this a case of one state following the other or did they both get it wrong independently?
For example all "Class B" implies is 2nd Order or less, 5th order (or less) can also meet "Class B" standards. In effect the reference/requirements should not be to "Class" but Order and where say "Class B" is specified then this should have been "Order 2", which by definition then requires a "Class B" survey or better
Standard 10 requires a Control Survey that should achieve a standard of accuracy as prescribed in ICSM, SP1 to Class D (u/g) / Class B (Surface) or better.
SP1 Class B or D is achieved by assessing whether the semi major axis of each relative standard error ellipse, is equal or less than the allowable semi major axis using the formulae r=c(d+0.2), where Class B, C=15, Class D, C=50 and d=distance in km.
So Class is a test on the control survey relative standard error ellipses. Any relative ellipses in a control survey that fail this test, would mean this control survey would not meet the standard of accuracy of a Class B or D control survey.
Yes survey "Class" is verified by analysis of a semi-major relative error ellipses based on a minimally constrained adjustment but at this point has no connection to datum so is an indication of internal fit only.
For this reason this term "standard of accuracy" used in relation to "Class" is a little misleading as "Class" is an internal relationship (determined from network design, survey methods, equipment, techniques etc) of the strength of the network but without connection to datum then accuracy of the station coordinates are not known at this point.
Order on the other hand is determined by a similar error ellipse analysis but based on connection to a known datum.
For example if our required "Class B" survey was then connected to Order 0 (Class 2A) marks then the best Class/Order that can be achieved is Class B, Order 2 eventhough the "accuracy" of the resulting coordinates are probably better than second order, the controlling factor in this example is the Class, being B
Connect this same Class B network to Order 5 control (or worse) then the best we can claim is Order 5 (or worse) even though the survey is to Class B the accuracy of the control is relative to the controlling marks. A similar scenario would also occur if the fully constrained adjustment error ellipse result indicated a poor quality Order, still Class B but poor quality coords yet meets the requirements of the legislation being Class B.
In both examples we still have the same survey Class but the resulting accuracy of the coordinates would be quite different and I believe this is why the legislation is not adequate in this regard, Class by itself does not control accuracy.
3.1 Mine coordinate system
All surface and underground surveys made and carried out in accordance with this standard shall
have a known and documented relationship to the MGA94.
All mine surveys and plans shall originate from the Mine Control Network. The connection of the
Mine Control Network to the state grid should be to Class B standards of accuracy as defined in
I cant fault your argument Kerry, as the connection from the state grid SHOULD be to Class B standards. It would be better if they used the word "shall" ?
Yes "shall" be to Class B standards would mandate the Class but still not control the Order. For this particular Class then words along the lines "Shall be to second order" would then mandate as a minimum Class B AND connection to at least second order control or better (typically including at least one first order mark).
Also the other thing that all this legislation will need to address in due course is the fact that SP1 version 2 (October 2013) supersedes the previous version 1.7 hence the move from Class & Order to Uncertainity. From what I understand (most?) state departments will now only publish Positional Uncertainties anyway.