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]

Calculate geometry, will just use the geometry and calculate X, Y coordinates... It knows nothing about datums.

Since Geographic Coordinates have a limited range of possible values, it just does the job.  Where that is located on earth physically depends on the datum.  So if your longitude and latitudes were given a WGS84 datum, then those same longitudes would be on a different location on earth if they were assigned an NAD27 datum.

In other words, the units are not the only important thing... the datum to which the values are referenced are also important.

When you go from Geographic to Projected coordinates, you have the datum issues as well as the unit issue... in your case... feet.

So know your coordinate units... know your datum for their values... and know what transformation to use if the datum is to change during the projection process.

The quickest way to get between locations on earth (instantaneously) is to simply change the datum  

[ChuckTurlington]

Dan,

My purpose for doing the transformation and projection from WGS84 to NAD83 is to get an export of the points so I can re-import into cad.  I am using the more superior ArcMap coordinate tools to perform the transformation/projection prior to importing into cad.  If I just change the GCS without explicitly transforming/projecting, my data will still reside as a WGS84 format, and will not give me what I need for a cad import.  Should I be transforming the data, and then due a projection as a stepwise approach or is there a better way than what I tried with the projection tool (assuming transformation is done in background).

[DanPatterson_Retired]

you can do the transformation as a one-step as long as the transformation is offered during the projection.

[ChuckTurlington]

Was that the problem with my attempt; the transformation was not available in the projection I was trying to do ?

[DanPatterson_Retired · Accepted solution]

I suspect so Chuck... sometimes it is best to follow the logical steps rather than make assumptions of things appearing as they should/might be expected.

You may be to the point that producing a Model or a script tool to automate the steps may be prudent... especially if things are going to be repetitive.

[MelitaKennedy]

Based on the attached picture, try deleting one of the two transformations. You're converting from WGS84 to NAD83. The first transformation converts from NAD83 to WGS84, while the 2nd converts from WGS84 to NAD83. Either one on its own is okay, together, they don't make up a valid path.

Melita

[ChuckTurlington]

Melita,

Thanks for your response, I really appreciate your thoughts on the subject and moral support most of all. Because I closed the online chain, I was unable to respond there, so will try this email, hope it is received.

I found that your suggestion does not resolve the problem, after tying it, I get the same error message. However, I think my earlier assumption may be the snag; assuming the software is making the transformation automatically with the projection. The explanation for the error appears at the right hand pane (see below screen shot), and is suggesting I should project from GCS_GRS_1980 to NAD_83_UTM_Zone_22N. However, the error still persists even with that workflow. I have had better luck with going from the GCS to GRS80 and then to state plane as a projection, but there was still a yellow shield error symbol. I think it is best to do the transformation explicitly first from WGS84GCS to GRS80, then project to NC Nad83 US Feet. Per our earlier conversations, I believe the vertical datum would be treated with a similar approach.

If you have any other suggestions or think I am off base, do not hesitate to let me know I am wrong. Thanks again for your help.

Regards,

Chuck Turlington

CAD Designer

[MelitaKennedy]

I  must not have read the thread thoroughly. I'm sorry, Chuck! If you have data with a GCS of "GRS_1980", that means it wasn't fully defined as GRS_1980 is an ellipsoid, not a geodetic datum nor geographic coordinate system. We don't have any transformations to/from GRS 1980 so you really need to redefine is as one of the NAD 1983 realizations, if you know which one it is.

Melita

[ChuckTurlington]

Melita,

My understanding is the geographic coordinate system is based on a 3d ellipsoid (correct me if I am wrong), that uses latitude and longitude.  My thought of using the GRS80 was to Transform the WGS84 ellipsoid GCS to another ellipsoid that is used as a reference for North America, GRS80.   Then perform a Projection from GRS80 to State Plane (NC) NAD83 US Feet.  I think you are saying I cannot go from WGS84 to a generic GRS80 unless it is associated with a defined coordinate reference system such as NAD83.  However, I am concerned that NAD83 is only a projected, grid type CRS and will not align well if I am starting with the WGS84 GCS.  However, I am assuming that the Projection option under the data management tools will not perform a transformation but only the projection.  If I need both transformation and then a projection, I assume I need to manually make those selections to perform each step separately.  If my understanding above is not correct, please inform.