I need to align an unprojected CAD file in ArcMap. I know how to adjust the False Easting and Northing, but this CAD file also has a rotation issue. I already adjusted the Central Meridian from -76.0 to -80.0, which helped, but it's still off. My adjustments of the Central Meridian parameter have all been trial and error.

Is there a way to measure the angular adjustment needed for the Central Meridian? See picture below:

CAD Rotation Issue

  • Did you get any sort of information about how this CRS is connected to a known one? translation, rotation, scale? Also send me an email, mkennedy at esri dot com, and I'll send you some documents about this issue. – mkennedy Aug 12 '18 at 18:36
  • For NYC, the only CRS we use is NY State Plane Long Island Feet. The newer CAD files from our surveyors were done accordingly, but I'm digging through the archive. Luckily, everything so far has been in feet, so I don't have to worry about scale. The translations are all over the place, but nothing I can't quickly fix with the false easting/northing parameters. It's helpful to have a bunch of custom .prj files on hand to quickly "try on" with each new CAD file. This is the first one I've encountered with rotation issues. – Priscilla Aug 13 '18 at 2:14

By 'unprojected', I assume you mean the CAD file is in a local grid that is not a recognised CRS. As I understand it, you're trying to define a custom projection that will align the CAD data to a known CRS for use in ArcMap.

Looking at your data, you could try georeferencing instead. By identifying known points in the CAD layer with corresponding locations in the target CRS then ArcMap can derive a best fit transformation that will shift, rotate and scale the CAD data so it will be 'aligned'.

See ESRI documentation for further information:

Fundamentals of georeferencing ArcMap 10.3

or there's the archives:

Georeferencing CAD datasets ArcMap 10.2

  • I started out trying to use spatial adjustment methods, but I got quickly frustrated by the output world files. I have a huge stack of CAD files to process, which all have slightly different spatial adjustment needs. The world files only seem to be reusable if your data have EXACTLY the same adjustment needs. I found that making my own custom .prj files was easier when I only needed to adjust the translation parameters or false easting/northing. Rotation adds a whole new layer of complexity though. Perhaps for this one case, it might be easier to create a world file. – Priscilla Aug 13 '18 at 2:28

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