RE: is there a way to export or create a datum so I can add that datum to V8i microstation

Frank Klein — Sun, 27 Jan 2019 10:26:25 GMT

Is it not possible to use an V8i NTV2 coordinate system and substitute the based *.GSB file. Seem to be a workaround. for Example:

...MicroStation V8i (SELECTseries4)\MicroStation\GeoCoordinateData\NewZealand\nzgd2kgrid0005.gsb overwrite it with the GDA2020.GSB and use the "newZealand" coordinate system. Just a Try.

RE: is there a way to export or create a datum so I can add that datum to V8i microstation

Alain Robert — Tue, 22 Jan 2019 14:13:07 GMT

It is possible to create custom datums and custom geographic coordinate systems in v8i SS3 and over, however to create these you need Bentley Map functionality. Once the user-defined coordinate systems are created then these can be used in any v8i SS3 and more Power Product.

In the case of the GDA2020 datum, it is quite easy to create. This datum is to be considered coincident to WGS84 over Australia (non transformation). The problem, however, is not defining this datum but rather a new version of GDA94 that will apply the correct transformation. The older GDA94 used to be considered coincident with WGS84 but after the various linear and non-linear movements of the Australian sub-continent it is not to be considered the case.

The most accurate transformation from GDA94 to GDA2020 relies on the application of a grid shift file in the NTv2 format. It is not possible to define a user-defined datum using this type of transformation. User-defined datum can only use simple transformations (Geocentric [3-parameter] or Coordinate Frame/Position Vector [7-parameter]). There exist such a 7-parameter transformation from GDA94 to GDA2020 and this particular transformation can be user-defined in v8i (with Bentley Map). Here are the parameters if this is the avenue you want to persue.

USE: 7PARAMETER
DELTA_X: 0.06155
DELTA_Y: -0.01087
DELTA_Z: -0.04019
ROT_X: -0.00394924
ROT_Y: -0.0327221
ROT_Z: -0.0328979
BWSCALE: -0.009994

To use the more accurate NTv2 based transformation CONNECT edition is necessary.