shrug-l: Surveyors, AARRGGHH!!!

[Tripp Corbin]

John,
I agree with Tim. The quickest and easiest solution is to spatially adjust the CAD file. IF you are running 9.2 then you must use the Georeferencing toolbar. If you are using 9.1 or earlier then you use the Spatial Adjust toolbar..
 
Tripp Corbin, MCP, CFM, GISP
Associate Vice President, GIS/Mapping
ESRI Authorized Instructor
Keck & Wood, Inc.
www.keckwood.com
(678) 417-4013
(678) 417-8785 fax
 
Keck & Wood, Inc offers instructor led and virtual training for ESRI's ArcGIS & ArcView software.
Please visit www.keckwood.com for more information including a schedule of upcoming classes.

________________________________

From: shrug-l-bounces at lists.dep.state.fl.us on behalf of Tim Spivey
Sent: Thu 7/19/2007 2:39 PM
To: shrug-l at lists.dep.state.fl.us
Subject: RE: shrug-l: Surveyors, AARRGGHH!!!


John -
If you have an ArcEditor license, I would do a Spatial Adjustment if you know where the CAD file should fall on the ground and have good reference points.
I don't even bother with projections for the CAD surveys we get, just the Spatial Adjustment tools.
The tools may be available at the ArcMap level, I'm not sure.
 
Tim

________________________________

From: shrug-l-bounces at lists.dep.state.fl.us [mailto:shrug-l-bounces at lists.dep.state.fl.us] On Behalf Of Sykes, John
Sent: Thursday, July 19, 2007 2:26 PM
To: shrug-L at lists.dep.state.fl.us
Subject: shrug-l: Surveyors, AARRGGHH!!!



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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