Here, cadastral survey work is to a local Geodetic Datum from which there is derived a cartesian system Map Grid which is based on the Gauss-Kruger Transverse Mercator projection:
- Latitude of Origin = 17deg17' south.
- Central Meridian 178deg45' east.
- Scale factor at Origin = 0.99985.
- False Northing = 4,000km.
- False Easting = 2,000km
- Ellipsoid of reference is WGS72 where a = 6,378,135m and 1/f = 298.26.
In the same source that the above information comes from, it goes on to give transformation parameters from WGS84 to the local Geodetic Datum:
- dX = +35.173m
- dY = -136.571m
- dZ = +36.964m
- Scale = +1.537 X 10^6
- Rx = -1.37 arc seconds
- Ry = +0.842 arc seconds
- Rz = +4.718 arc seconds
We (engineers, not surveyors, so apologies in advance for lack of understanding) work with both the local Map Grid and WGS84, the latter more commonly for maritime work. My question that hopefully someone can assist with relates to recent Civil3D transformation that we have done from the local Map Grid to WGS84. The outcome of that Civil3D procedure for say a building layout is that it appears to yield a rotation of around 1 degree. Is there something in the above parameters that suggests that this rotated outcome is correct?
Grid North and Geodetic North only match at the Central Meridian, Longitude 178d45' E.
What Longitude are you working at?
James
Thanks. It is 177d23'E. (I think I can visualise what you are referring to). Perhaps I should also state more correctly that the Civil3D transformation was from the local Map Grid to WGS84 UTM 60K.
Another edit, error in subject title (WGS82) WGS84.
Also note that WGS84 and its predecessors are not fixed to a tectonic plate as is our NAD83. Thus there is a coordinate drift of some magnitude over the years as well as the refinements in the updated definitions. In the central US it is a couple cm/year.
Thanks. I'm still battling with this, leaning towards it being a Civil3D issue. But one good thing is that I have delved into Civil3D's survey functionality - first impression is that it does everything a surveyor would want, in spite of it apparently getting a bad wrap.
