In 4.3 of the Surveyor Generalís Directions to check the coordinate accuracy of the GNSS observations against the SCIMS coordinates, dsistances between the survey marks are used to determine discrepancies with coordinates. For traverses this is fine since errors are greater for long traverse lines. However errors in GNSS observations are not dependant on the distance between the survey marks but rather the distance between the rover and the CORS station. As such it would make more sense to calculate the ppm component using the distance between the CORS site and the survey mark rather than between survey marks.
Also in 4.3 of the Surveyor Generalís Directions it is advised that Permanent Marks should be used in preference to State Survey Marks due to superior stability. While it is true that PMs are less likely to be disturbed than SSMs, PMs can be covered with dirt and water which makes it difficult to pinpoint the centre of the mark, thus weakening the recommendation of PMs over SSMs.
With 6.1 of SGD, using another CORS site is a good check. However it should be noted that the other CORS site needs to have similar physical characteristics such as similar distance from the rover, otherwise differing results will appear. Although differences will occur the measurements should still achieve the required accuracy.
In an ideal world the author would recommend that the minimum accuracy to be achieved is changed such that the ppm component would be calculated between the CORS site and a survey mark. This would ensure that distance-dependent errors that occur due to the rover and CORS site being far apart would be factored into the accuracy check of the coordinates for the rover. However due to the heritage of the geodetic control survey network which comprises older observation techniques and inferior precisions, the adjusted coordinate set that makes up the SCIMS database are distorted. This distortion is noticeable over the distances spanned in the CORSnet-NSW network using RTK GPS techniques. So a surveyor adhering to a SCIMS coordinate will notice a difference in the field using a CORSnet-NSW derived RTK solution. A site transformation therefore "scales" these observations to fit with local control. It could be argued that this is a degradation of a good solution, however most survey operations should fit locally and this technique allows this to occur.
CORS networks will continue to become a widely used tool as they eliminate the surveyorís responsibility for the reference station and are easy to connect to. Regulations will need to be reviewed in the future as technology evolves and new techniques are implemented. A review of regulations and the assumptions used to write regulations would also be necessary if the dynamic datum proposed by Johnston and Morgan (2010) is adopted to investigate the effect that such a datum would have on surveying practices and their compliance with the regulations.
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