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Regardless of what you've read, heard or are told by others, 'plain vanilla Acad' cannot save a your drawing with a georeference. This is because plain vanilla Acad doesn't have the capability to georefeference the dwg like Civil 3D or Map 3D. This, however, doesn't necessarily mean you can't 'fake-out' Global Mapper into thinking you are, indeed, using a 'known datum.'
If both of the following conditions are present in your Cad dwg:
1.Your x and y coordinate values coincide (or are identical) to a projected coordinate system that uses either feet or meters (as opposed to a geographic-coordinate-system-which-use-degrees) such as State Plane or UTM, then you can do it. If your drawing x's and y's are NOT coincidental, then it means your drawing's line work has been arbitrarily a) positioned, b) rotated and c) scaled in modelspace, and in cases such as these, you can't do it. Just because you can open the dwg or dxf in GM doesn't mean GM will magically provide a georeference.
2.You configure or assign the correct State Plane or UTM Zone to Global Mapper when opening the dwg or dxf in GM. For example when opening a dwg/dxf that is NOT georeferenced in Acad, the GM configuration looks like this:
Glo Map configuration=>then Projection from panel on left.
If you are trying to establish a georeference to an un-referenced dwg, then you cannot simply force Global Mapper create a georeference for you because your dwg didn't provide the geospatial parameters which GM needs to do so.
2-This is the dxf in Vanilla Acad.
3-This is dxf 'opened' in GM. (Imagery added usnig GM.)
In 2 and 3 above, you can see the coordinates of that the blue point in vanilla Acad has transferred over to Global Mapper. If the coordinates in Acad were NOT correct, then they wouldn't be correct in GM either. The blue point is NOT arbitrary, it has been placed at those coordinates on purpose. On purpose=coordinate geometry 'know-how.'
NOTE: Earlier, in the configuration=>projection dialog of GM, the appropriate State Plane and Zone, which happens to be Texas State Plane, Central zone, was established. (Again, knowing the correct St Pln and zone='know-how.' ) If it wasn't established in GM then the Cad line work wouldn't be correct because GM would've positioned the line work arbitrarily.
The key to this entire exercise is the Blue Point, or some other reference point, MUST have Coordinates that coincide, or are equal to State Plane, so that Global Mapper will treat those x and y numbers as State Plane. By treating those x/y's as State Plane you have effectively 'faked out' GM into thinking your drawing is georef'd even though your program, vanilla Acad, doesn't have the capability to GeoRef in the first place.
If you cannot get the blue dot accurately placed in Vanilla Cad, or you don't know how to place it even though you have the coordinates, then, sorry, you are stuck with a non-georef'd dwg.
Chicagolooper