Converting reference drawing from grid to ground

[Anonymous]

I was given a file that was done in grid but our files were done with a surface adjustment factor to ground. I have the adjustment factor however I would like some guidance on how to apply this factor to my reference drawing. Thanks for your assistance.

[Mike.M.Carlson · Accepted solution]

Hello,

If your "GRID" dwg has a lot of geometry, I would recommend attaching\scaling and\or rotating that as an XREF into your "GROUND" dwg.  If you have cogo points in the GRID dwg or need to convert a C3D surface to the ground file, I would use the Survey Data base\Transformation Tab to dial it in.  Both options require the following:

1. Base Control Point (usually given by the surveyor that is at the project centroid) to apply the Combined Ground Scale Factor and/or rotation.  You will need the N,E,Z both in GRID and GROUND for this point. 
2. Verify if there is a rotation as well.

Going from GRID to GROUND you will need a combined scale factor that is calculated by 1/0.99999xxxxx.  Again this is given by the surveyor. The resulting scale factor (1.0000xxxx) needs to be applied at the Base Control point (Ground location) after translating the GRID XREF into the GROUND coordinate system. 

Let me explain...Once you XREF the GRID dwg into the GROUND dwg, you will see the GRID XREF in wrong location.  That is ok, you're going to translate the GRID XREF (using the "Base Point" mentioned above as the move point from the GRID position to the Ground position). Once GRID XREF is translated to the GROUND XY system, you would then apply a rotation, if needed from the same base point.  Be careful when applying the scale factor so that you only apply the factors to X,Y direction.  Leave Z axis alone for this.

I hope this helps.

[ChicagoLooper]

 @Mike.M.Carlson you are spot on, as usual.

Here's another way to move from grid to ground. It uses a 'copy' of the existing grid, typically State Plane, and 'adjusts' it to be consistent with ground units. The adjustment merely takes the State Plane grid and scales it to ground.

To see how it's done, >>click here<< to watch the video.