DGN to GIS with Affine Processor

[ZachCrimmins]

I work in Colorado where it's common for project survey data to be delivered in truncated state plane coordinates. Truncated meaning the surveyors remove between 1 and 3 million feet from the N: & E: coordinates. If not adjusted for, CAD linework shows up somewhere in AZ generally. I have been trying to define a workflow to get project data lined up in ArcGIS and have been having a heck of a time. Our CADD is done in Bentley OpenRoads Designer primarily.

In CAD, I get my aerial background to consistently line up with the data by assigning the appropriate state plane system (ex. NAD_1983_HARN_StatePlane_Colorado_Central_FIPS_0502_Feet) and then applying an affine processor that defines a ground adjustment factor and horizontal and vertical offset as A0 and B0 values respectively. Example shown in 1. ORD GCS Setting.png. In this example the data was truncated by 2 million units X and 1 million Y with a GAF of 1.00048188. This works great for CAD! The issue is that when I export the data to a SHP, it goes with a .prj file that ArcGIS can't recognize (2.Topo.txt - changed to txt for upload, normally a .prj). I think ArcGIS can only recognize basic projections and not projections with affine modifiers.

So I need a way to define an affine transformation in ArcGIS, either to the basemap or data being brought in. I thought I could do with a .wld3. I found this article that shows a similar workflow to define a transformation with a raster but can't get my data to use it. World files for raster datasets—ArcGIS Pro | Documentation 

Is there a different way I might go about this or make this work? My goal is to not have steps in my workflow that people might do differently like choosing points in the CAD linework and connecting them to where they belong in GIS. I'd like for three people to be able to follow and get the same result and doing some sort of affine conversion based on survey data seems like the best way to do that.

Any help would be greatly appreciated. Also, I am new here so if there's a better place to post this inquiry please let me know.

[KyleGonterwitz]

I used to do something like this, my scripts for it are at https://github.com/KDOTGIS/pydot/tree/master/CoordinateDGN

IT was over 10 years ago, but this was at the time a way to edit the proj file in ArcGIS to adjust coordinates with a CAF, including the false northing and easting, with results equivalent to the Affine transformation in MicroStation.  Eventually Microstation became able to export a KMZ file which made this process unnecessary.