NAD27 coordinate system

[JamesHarrington]

Hello -

I have a set of points in a table with coordinates that are Connecticut State Plane NAD27 Feet. They get projected in the wrong location, about 125 feet to the southwest. When I transform the coordinates to WGS84, using the Project tool or Corpscon 6, they are in the right place. Something is not right with how ArcMap is projecting the NAD27 system. Any way to correct this?

[JoeBorgione]

What do you mean they are in the wrong place?

Am I correct in thinking you are adding the nad27 data to a nad83 data frame? If so, your complaint is that the projection on the fly feature of ArcMap isn't meeting your expectations: is that correct as well?

Personally, I'd chalk it up to the difference in datums and not worry about it; 125 feet?  What is the precision of the original data?  What are your precision needs for this data?  Seems to me you've resolved the issue by projecting it.

[JamesHarrington]

What I mean by '...in the wrong place' is exactly what I said, the points are 125 feet southwest of where they are in reality.

You are incorrect - I am adding the data to a NAD27 Data frame. The precision of the original data is 1 ft. I expect the precision to be within 3 feet.  We have field staff who will need to locate these points, and 125 feet is not acceptable. I think the data should be projected correctly in the first place without my having to go through a third party to correct it.

[JoeBorgione]

Okay, I see your point (all puns intended). Certainly didn't mean to burr you up;  perhaps using a tablet sized map or similar sized paper map to locate points to the precision needed isn't the way to go.  If you need to locate to a foot, a survey grade GPS is what I would deploy.

[MelitaKennedy · Accepted solution]

James,

Are you setting a transformation in ArcMap to convert to or from WGS84 (or NAD83)? ArcMap doesn't set any transformations by default. Try setting NAD_1927_To_WGS_1984_79_CONUS or whatever you used in the Project Tool.

Melita

[JamesHarrington]

Thank you - that worked amazingly perfect! Now I think I may have an issue if I add any data that is NAD83, but I think this entire set is NAD27. At least I know there is a quick soloution now, THANKYOU!!!

[JamesHarrington]

Update:

I added some data in NAD83 and it projected correctly even with this transformation, so it looks like all my problems are solved - thanks again!