In late 2016 it was discovered that project survey data was being transformed when coordinate systems were not being used uniformly throughout a Civil 3D project. This transformation occurs when the coordinate system selected for a LandXML import differs from the coordinate system assignment for a survey database. The transformation also occurs when data from a survey database is inserted into a dwg file that has a coordinate system assignment different from the survey database. For more information on the issue and what can be done to identify and resolve the issue refer the following C3DKB topics:
The WisDOT Methods Development Unit and Surveying and Mapping Section has coordinated with Autodesk to identify the source of the unintended transformations. The source of the unintended transformations depends on the coordinate systems that are selected.
Issue #1
Civil 3D is shipped with a coordinate system category called "USA, Wisconsin". This category of coordinate systems includes two series of Wisconsin County coordinate systems. Examples:
Figure 1: Original Civil 3D prepackaged coordinate systems used HPGN datum (NAD 83/1991)
Figure 2: Autodesk later introduced coordinate systems that use state-specific HARN datums (NAD 83/1991)
While these two systems have different datum assignments (HPGN vs HARN/WI), the two datums are equivalent, both based on NAD83(1991), and only differ by name. However, it was discovered that the transformation definitions into and out of these two datums are not equivalent in Civil 3D. In the example above, the transformation definition into and out of the "Wisconsin Ashland, US FT (or use HARN/WI.AshlandWI-F)" is based on a series of grid files for every state. Civil 3D processes the grid files in an order defined by the transformation definition. Since the grid files overlap, and the Wisconsin grid file is near the bottom of the list, the transformations often occur based on another states grid file. Therefore, this transformation definition is not correct. For the "Wisconsin County Systems: Ashland County, US Foot" example, the transformation definition is correctly defined by a single grid file specific to Wisconsin.
Issue #2
In 2016, WisDOT deployed its own set of coordinate systems in Civil 3D. These systems are organized in categories that begin with "WisDOT". Within these categories, there are two county systems, "WCCS" and "WisCRS". Each of these coordinate systems, regardless of which "WisDOT" category they fall into, are defined by the Civil 3D NAD83 datum. The NAD83 datum in Civil 3D is based on the 1986 adjustment year.
Figure 3: In 2016, WisDOT introduced coordinate systems using the Civil 3D NAD83 datum (NAD 83/1986)
Since the coordinate systems located in the "USA, Wisconsin" category use Civil 3D datums based on the 1991 adjustment year of NAD 83 and the coordinate systems that WisDOT provided in the "WisDOT..." categories are based on the 1986 adjustment year of NAD 83, a transformation occurs when moving data between these systems.
Introduction
