AutoCAD Civil 3D General Discussion

AutoCAD Civil 3D General Discussion

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*Expert Elite*
AllenJessup
Posts: 5,872
Registered: ‎05-21-2003
Message 1 of 3 (413 Views)
Accepted Solution

Point shift on Land Desktop (LDD) convert

413 Views, 2 Replies
10-05-2011 09:59 AM

I solved this one already but I’m going to post it in case it helps anyone in the future.

 

We had a small project done in 1992 and based on an arbitrary coordinate system. In 1996 we took off the control from that work and did a mile and a quarter of topo & right of way work and 7.4 miles of traverse. The traverse picked up existing monumentation in NAD27. Based on those monuments the drawing was transformed in to NAD27. This was a local system based on NAD27. We’re close to sea level and the Geoid so we don’t bother with scale factor.

 

About 7 years ago we occupied some of the control points with GPS and the project was transformed to a local system based on the NY-HARN. This was part of a project to bring all our lager jobs in to this system.

 

We’re looking at doing more work in the area so I needed to bring some of the points in to Civil 3D. All the points were in one drawing so I inserted that drawing in to a new drawing created from our template. When I tried to convert the Land point in to Civil 3D points. There was a dramatic shift in the coordinates.

 

It looked like you might expect from a drawing that had had a Base Point and/or North Rotation set in Land. We NEVER used BPNR but I checked anyway but found none was set. One thing I noticed was that he coordinates, after conversion, looked like what I’d find in one of our old arbitrary systems. I dug out the old drawing we started from and matched a traverse point exactly. Somehow the coordinates from that old job were following the points in to Civil 3D and being used in the conversion.

 

When I opened the project that had been transformed to the NAD83-HARN and listed the points in Land, the point coordinates were correct for the local NAD83 projection. I finally listed a point with an AutoCAD List and saw that the coordinates were listed as the old arbitrary system and the point maker coordinates were correct for NAD83. While this still looked like a BPNR situation, I confirmed that none was set in the Land drawing.

 

I solved the problem by deleting the points from the Land drawing and reinserting them from the Database. The Northing/Easting listed with an AutoCAD list command now matched the marker insertion point and the correct NAD83 Coordinates. I inserted that new Land drawing in to a Civil 3D drawing and the conversion executed correctly. It looks like that routine uses the coordinates listed in the point rather than the insertion point.

 

Hope this helps someone at some time.

 

Allen

 

 

Product Support
SethHall
Posts: 723
Registered: ‎02-08-2010
Message 2 of 3 (399 Views)

Re: Point shift on Land Desktop (LDD) convert

10-05-2011 11:54 AM in reply to: AllenJessup

Hi Allen-

 

This is great! Thanks so much for posting this... I am sure it will help someone out at some point in time.

 

Thanks again!!!



Seth Hall
Product Support
GCSO - CSS - FTS
Autodesk, Inc.


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*Expert Elite*
AllenJessup
Posts: 5,872
Registered: ‎05-21-2003
Message 3 of 3 (396 Views)

Re: Point shift on Land Desktop (LDD) convert

10-05-2011 12:03 PM in reply to: SethHall

Thanks Seth. I hope it does. It took quite a bit of head scratching to figure this out.

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