Converting NAD27 XY values to to NAD83 XY Values

Question

Hi,

I have XY value tabel having with NAD 27 Zone 6, I want convert this vales to NAD 83 Zone 6.

Thanks,
GM

MelitaKennedy · Answer

I have a project that gave me a table of xy values in NAD27, Pennsylvania State Plane (Foot). They would like the coordinates converted to NAD83, PA State Plane (Foot). I need some one to check this for the correct steps.

This is the process that I did:

Open an MXD file and set the projection to NAD27, PA State plane (foot)
Bring in the table from Catalog
Right click on the table, then Display XY data, and set the the appropriate x and y fields.
Export the data to change it from and event to a shapefile/feature class in NAD27

Open an MXD file that is set to NAD83, PA State plane (foot)
Import the previously created shapefile.
Export the shapefile ensuring that the projection for the export is the same as the data frame (NAD83) and NOT the source (NAD27).
Create two fields in the attribute table for new x and y values
Calculate the geometry of these field using the appropriate data.

These values are now in the NAD83, PA state plane (foot) but they are slightly different than another check that I have (from the client).

Can anyone point me in a different direction or confirm my method? Thanks

I think this thread should be moved to the general Desktop queue because you're not using ArcObjects. If you agree, I'll move it.

Anyway, the order looks good although I have two comments. Make sure that the geographic (datum) transformation is set to convert between NAD 1927 and NAD 1983. Open data frame properties, Coordinate System tab, and click the Transformations button. In the top box, make sure NAD 1927 is selected. The middle pull-down should list NAD 1983. The transformation pull-down should have NAD_1927_To_NAD_1983_NADCON.

If the values are still off (how much?), ask the client if they really want a more recent re-adjustment than NAD 1983 (1986 aka the original). It's possible they want something like NAD 1983 HARN, or later.

The 2nd comment is that you don't need to use two documents. Once you have the shapefile/feature class, change the data frame's coordinate system to the coordinate system you want to use and export the data the same way.

Melita

EricOliver · Answer

I have a project that gave me a table of xy values in NAD27, Pennsylvania State Plane (Foot). They would like the coordinates converted to NAD83, PA State Plane (Foot). I need some one to check this for the correct steps.

This is the process that I did:

Open an MXD file and set the projection to NAD27, PA State plane (foot)
Bring in the table from Catalog
Right click on the table, then Display XY data, and set the the appropriate x and y fields.
Export the data to change it from and event to a shapefile/feature class in NAD27

Open an MXD file that is set to NAD83, PA State plane (foot)
Import the previously created shapefile.
Export the shapefile ensuring that the projection for the export is the same as the data frame (NAD83) and NOT the source (NAD27).
Create two fields in the attribute table for new x and y values
Calculate the geometry of these field using the appropriate data.

These values are now in the NAD83, PA state plane (foot) but they are slightly different than another check that I have (from the client).

Can anyone point me in a different direction or confirm my method? Thanks

MelitaKennedy · Answer

Hi,

I have XY value tabel having with NAD 27 Zone 6, I want convert this vales to NAD 83 Zone 6.

Thanks,
GM

You'll want to look at IGeometry2:ProjectEx. By Zone 6, do you mean a state plane zone? Possibly in California or Alaska? Here are some snippets. The first creates a projected coordinate system based on NAD27. Private Sub CreateProjectedReferenceSystem()
    ' Set up the SpatialReferenceEnvironment.
    ' SpatialReferenceEnvironment is a singleton object and needs to use the Activator class.
    
    Dim t As Type = Type.GetTypeFromProgID("esriGeometry.SpatialReferenceEnvironment")
    Dim obj As System.Object = Activator.CreateInstance(t)
    Dim srFact As ESRI.ArcGIS.Geometry.ISpatialReferenceFactory = obj
    
    ' Use the enumeration to create an instance of the predefined object.
    
    Dim projectedCS As IProjectedCoordinateSystem = srFact.CreateProjectedCoordinateSystem(esriSRProjCSType.esriSRProjCS_NAD1927SPCS_CAVI) ' California 6
End Sub

The enumeration for NAD83 California 6 is esriSRProjCS_NAD1983SPCS_CAVI. You'll also want to look at

Understanding geotransformations

which has a link to code on how to create an existing transformation. If the data is in California, you'll want to use esriSRGeoTransformation_NAD_1927_TO_NAD_1983_NADCON.

Melita