South Africa Civil 3D – Revit Link Shared Coordinates and Topography
South Africa has a coordinate system that is not consistent with the way in which software is programmed. x points South, y points West and z down into the ground. To get around this in Civil 3D, for instance, the South African Country Kit maps the x-axis to the y-axis and the convention in South Africa is to list the y ordinate before the x ordinate.
I did not have trouble opening an Infraworks model in Civil 3D (where the Civil 3D file is using the South African Definition). Here is Cape Town international. In the right view port the Infraworks model is superimposed on the Civil 3D online map image. They correlate using the WSG84 Lo19 coordinate system even through the Civil 3D model is using the South African Definition. The little white pentagon was drawn to represent a new building that is to be constructed in Revit. A line is drawn from the origin (survey beacon) to one of the corners of the pentagon to act as a visual reference when the coordinates are shared into Revit.
However, some of the latest BIM workflows between Civil 3D and Revit does not work for the South African coordinate definition. Specifically:
Here is the pentagon as seen in Revit before the Civil 3D coordinate system is shared in through an XML file.
When the coordinate system is shared in this is the result. The Pentagon is pointing South, instead of North.
Linking in a published topographical surface is can be seen that the pentagon is pointing North instead of South.
To try to fix this, the model is rotated through 180⁰ and change the Project Base Point, multiplying the northing and easting by negative 1.
The topography is now in the wrong position, but at least the pentagon is pointing south.
If the link is removed and then once again established, the following error is generated:
And a warning
After which the topography is placed at the “center to center option” (the center of the little circle)
Also, if the shared coordinate is once again inserted from the XML file, the transforms manually applied to the coordinate system is lost.
Clearly a change in the coordinate definition of South Africa would make many people’s lives easier, and software more readily accessible, but from many conversations with those in the Industry, this is a decision that will have to be driven by the powers that be.
In the meantime, test the tools to see if you can get them working. If you don’t, and until such a time that these tools work for the South African environment, preferably steer clear of using them professionally, and don’t write them into your BIM protocol. Instead default to the tried and tested methods south Africans already use. One can still import the topography, translate and rotate it within Revit and then update the link (it just will not link in automatically according tot he shared coordinate system).
If you need help coordinating BIM files, please contact Micrographics so we may be of assistance.