ArcMap-Projection

[ChuckTurlington]

Hello,

I am using ArcMap 10.4.1.

I am performing a projection from WGS84 to NAD83, NC, USFeet.  The projection dialog is shown in the attached screenshot.  The data I am trying to project did not initially have coordinates but I was able to perform a "calculate geometry" to establish the latitude and longitude in the attribute table of the data.  However, I am unclear why the projection does not appear valid, yet I am meeting the criteria, as far as I know.  Any suggestions are welcome, thanks in advance for your help.

[DanPatterson_Retired]

Chuck.. Melita is saying that you need to define the GRS80 as one of the NAD83 versions.  This help topic

http://desktop.arcgis.com/en/arcmap/latest/map/projections/north-american-datums.htm provides some background as do other links in the same area.

particularly

The GRS 1980 spheroid is almost identical to the World Geodetic System (WGS) 1984 spheroid. The WGS 1984 and NAD 1983 coordinate systems are both earth-centered. When originally published in 1986, NAD 1983 and WGS 1984 could be considered coincident. That is no longer true. WGS 1984 is tied to the International Terrestrial Reference Frame (ITRF). NAD 1983 is tied to the North American tectonic plate to minimize changes to coordinate values over time. This has caused NAD 1983 and WGS 1984 to drift apart. Generally, coordinates in WGS 1984 and NAD 1983 are around one to two meters apart. GPS data is actually reported in the WGS 1984 coordinate system. However, if any type of external control network is being used, such as the Continuously Operating Reference Stations (CORS) service, the GPS coordinates are relative to that coordinate system, not WGS 1984.

[ChuckTurlington]

Dan,

I find the "Project" tool in ArcToolbox, is being referred to as a transformation tool.  Is the term "projection" and "transformation" being used interchangeably here, or is there a method for just performing transformations?

[MelitaKennedy]

Misleading and overloaded terminology. I use "projection" as much as I can to mean converting between lattiude-longitude (referenced to a geographic coordinate system) and xy, 2D Cartesian coordinates referenced to a projected coordinate system. I use transformation or more liked a geographic/datum transformation to refer to when we're converting between two geographic coordinate systems like NAD83 and WGS84. The Project tool will also perform transformations if the input and output coordinate systems (geographic or projected) have different geographic coordinate systems. You don't need to perform them separately. 

Geographic/datum transformations, depending on the method type, either explicitly convert between the two ellipsoids as part of the algorithm, or it can be considered to be included into the method implicitly. An explicit method would include geocentric translation where you convert the latitude-longitude into 3D Cartesian, XYZ, using the input ellipsoid. offsets are applied to the XYZ values, then the XYZ values are converted back to latitude-longitude using the output ellipsoid. An implicit method would include any file-based method like NADCON/HARN or NTv2 where a grid file is used to calculate the offsets. The ellipsoid change is just included in the offsets.

Maybe look at a presentation like Introducing Coordinate Systems and Transformations. Start here and search using 'coordinate' (without quotes).

Melita

[DanPatterson_Retired]

Forgot this http://desktop.arcgis.com/en/arcmap/latest/map/projections/choosing-an-appropriate-transformation.ht...