Geocoordinate Systems, back to Placemarks does not work?

Question

Brief description: 
 MicroStation V8i SS2 and a DGN with local coordinates. xy aligned to buildings, GO close to buildings 
 
 I add 3 placemarks to connect datapoints with real world coordinates: 
 Cartesian system, EPSG:31467 
 Entering the coordinates, verify calculated long/lat values and place the placemarks 
 I select GCS "from placemarks" 
 
 Fine. 
 
 Now I change the GCS, "from library", select the same EPSG:31467 and OK 
 In the dialog, I choose "reproject". All Geometry is now rotated and moved. I select the ACS related to the GCS and assign it. 
 
 Fine. All input and output now is in real worls coordinats, easting and northing. If I activate "report ACS Position" I can see longitude and latitude. All at the correct positions and true north. Fine. 
 Now the problem: 
 If I want to go back to my original local coo system, it doesnt reproject. 
 
 I select "GCS from placemarks", they are still there. I OK that. 
 Dialog asks, I select "reproject". Progress bar shows processing. 
 
 But nothing changes anymore. I'M stuck with the real world coordionates. The elements dont rotate back, they are not moved back to the local coordinates. 
 A bug? WAD? Another way to go back? 
 Thanks, Bigean

Barry Bentley · Accepted Answer

Bigean, 
 The way the placemarks work is that the X,Y (cartesian) coordinates are determined by the position in the design file and Lat/Long (Geographic) coordinates from the value stored in the placemark. When you create a Geographic Coordinate System from placemarks, it essentially calculates a best fit Azimuthal Equal Area coordinate system that makes the Cartesian coordinates map to the Geographic coordinates in the placemarks. But when you reprojected to EPSG:31467, you changed the Cartesian coordinates of the placemarks, so the Cartesian inputs to the calculation are changed, therefore you are not going to get the same calculated coordinate system from the placemarks. IMO, Backing up a design file before reprojecting the contents is always a good idea. 
 Barry Bentley

Barry Bentley · Answer

One way to do this is to make a design file (say StructureGCS.dgn) with your "structure centric" GCS in it. When you want to put that GCS into another design file, attach StructureGCS.dgn coincidentally, and then when you assign a GCS, use the "From Reference" option (just to the right of the "From Placemarks" icon.) 
 HTH 
 Barry Bentley

Bigean · Answer

Unknown said: One way to do this is to make a design file (say StructureGCS.dgn) with your "structure centric" GCS in it. When you want to put that GCS into another design file, attach StructureGCS.dgn coincidentally, and then when you assign a GCS, use the "From Reference" option (just to the right of the "From Placemarks" icon.) 
 Hi Barry, 
 yes, that is the solution. 
 1. Before transforming a placemarked DGN into a world coo system, save that DGN as a future template for the local coo system 
 2. Going back from world to local coordinates requires to attach that template DGN as reference, method coincident, and then "set GCS from reference", choose "reproject yes", which transformes back. 
 In step 2 I also tried to "import from DGN" method, but that results into a bad accuracy for the backtransform. One should not use that method. 
 Thanks, Barry, I was able to understand why it didn't work and how to proceed another way. Great Knowledge that you have, I'm impressed. 
 Bigean