Co-ordinate System [South African]

Hi,

Hartebeesthoek94 is the right projection, the co-ordinate system is Lo25 for the file, which I have posted.

Both Hartebeesthoek94 and Cape datums will have Co-ordinate systems from Lo17 till Lo 33.

We capture co-ordinates in one or the other datum and have to be able to convert captured datasets from Hartebeesthoek94 to Cape and vice versa. The X (South) co-ordinates in Hartebeesthoek94 projection will be always about 300m to the South in relation to Cape datum; there is difference of few meters only for  Y co-ordinates (East-West) .

I did not reply further about Codes, as I am not using them and can't provide any guarantee on their relevance.. On your request - I have tried to find them. The ones, which you have mentioned seem to be closest to what we are using. 

Also, I have tried all possible options from the Library before posting this query. 

Kind regards

Bronia

Hi again, I forgot to answer about co-ordinate values - they are correct in posted dgn file. It can be checked against grid values in models.

Przytula,

The official definitions for most coordinate systems in South Africa (EPSG:2046 to 2055) are defined with Y ordinate decreasing Northward and X ordinate decreasing Eastward. Yet, this seemed unnatural to some of our clients in South Africa that still wanted the up of the screen to be in the Northward direction (and right toward the East). MicroStation and most design software deal poorly to satisfy both conditions. It is possible to mimic some of this behavior by defining rotation to views, or making use of ACS to input coordinate differently but those remain adaptations that are not always satisfactory.
Some clients requested instead that we provide versions of South Africa coordinate systems but with the more usual convention of X ordinate increasing Eastward and Y ordinate increasing Northward by modifying the coordinate signs. This is the reason we provide two versions of Hartebeesthoek94 zones. For Lo25 these Geographic Coordinate Systems would be Harte1994.Lo25 for the official definition (Y decreasing Northward) and the version with more normal convention Harte1994.Lo25-A . I have opened the file you provided that initially made use of the later version (normal axis convention) and displayed with Bing Map (Background Map in View settings) and the model fit with ground features.
I have reprojected the file to the official definition with Y ordinate decreasing Northward and this result into model elements displayed upside down yet still be perfectly alligned with Bing Map ground features but with North being toward the bottom of the screen.
The important part is that in both cases the model fits with ground features. After that it is for you to decide if you prefer keeping official coordinate signs and configure a workable environment using view rotation or keep North to the bottom of the screen as you see fit or use inverted sign of coordinates.
Note that the same adaptation has been made for the zones using the CAPE datum. The official CAPE datum would be CAPE/GSB so the equivalent coordinate systems would be CAPE/GSB-Zn-25 and CAPE/GSB-Zn-25-A depending on the axis convention you retain. Note that the CAPE/GSB datum makes use of the SA.GSB grid shift file in NTv2 format. This grid file is not provided with Bentley Products since the property of the file is uncertain (it was [apparently built by ESRI South Africa probably for the South African government). You locate the SA.GSB file yourself and place a copy of it in the GeoCoordinateData/SouthAfrica/ directory of your software (may require administrator privileges).

Aiain