shrug-l: Surveyors, AARRGGHH!!!

[Sykes, John]

I just received an AutoCAD file of a survey produced in the late 1980's.
Additional field work was done in 2004 and this revised survey is the CAD
file I have.

I assumed the survey work was done in State Plane Coordinates NAD83, but when
I created a projection file for this survey it ended up about 30 miles west
of the site when I let the file project on the fly!

So I went back and created a new projection file, this time establishing the
coordinates as State Plane Coordinates (SPC) NAD27.  When I imported the CAD
drawing I immediately saw that the CAD drawing was coming out southwest of
where it should be by about 50 ft.  I realized that the surveyor apparently
had taken a SPC NAD27 file and offset it by the correction factor from NAD27
to NAD83 without taking into account the difference in the offset that also
exists between the two projections (I have been told that this 30 mile offset
was added to the SPCs to make if obvious when the wrong projection was being
used).

The problem is that, if I reproject the SPC NAD27 file to SPC NAD83, it adds
the offset between the two datums back in again!!!  Short of getting the
surveyor to correct their file (not likely since the job was finished in
2004) how do I get this error corrected???

By the way, I tried telling the PRJ file that the coordinates were SPC NAD27
and the datum was NAD83, but that didn't work.  Also, I found that the
reprojection tool in the toolbox doesn't work for CAD files.

Of course, ultimately I'm trying to get this whole thing into FDEP Albers for
my map.

-- John

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