Converting NAD83 to WGS84 ArcMap vs ArcPro

[MalcolmMeyer2]

Converting from NAD 83 Ohio SP South (NAD_1983_StatePlane_Ohio_South_FIPS_3402_Feet) to WGS84 creates different outputs in ArcMap compared to ArcPro. When opened in ArcPro the file appears to be the same (it must be doing a projection on the fly), but when examining the data further, either by exporting it out as GeoJSON or opening it in QGIS, the exported WGS84 file is shifted slightly northwest by approx 3ft. The same file exported using the same process in ArcMap does not shift.

I am using Feature Class to Feature Class, and the environment settings to change the projection.

In ArcMap it the default Geographic Transformation method if nothing is selected is NAD_1927_To_NAD_1983_NADCON. Using this transformation in ArcPro does not help.

The attached files are the result of the Features to JSON tool, run in ArcMap for the ArcMap converted file, and Pro for the Pro converted file, with GeoJSON checked, and in Pro, the Project to WGS84 unchecked. The difference is dramatic.

[Scott_Harris]

Hi Malcolm,

I tested with my own points in NAD_1983_StatePlane_Ohio_South_FIPS_3402_Feet in ArcMap 10.6 and Pro 2.2.4, but got the same output from the Feature Class to Feature Class tool in both programs.

Some questions:

1. In the tool, are you referencing the layers in the map or the feature classes on disk?
2. Can you provide a screenshot of the tool environments you are using?

[MalcolmMeyer2]

Hmm, thought I replied to this already. Anywway the problem is noted here - coordinate system - Transforming GCS_North_American_1983 to GCS_WGS_1984 using ArcGIS Desktop? - Geo... 

Specifically - "Transformation 2 for CSRS and ITRF00 for NAD83 (original) are the default transformations in Esri software now." However, ArcMap does not have a default transformation set. Setting this transformation to "None" in ArcGIS Pro seemed to fix the issue for me, at least at the moment.

[MattWilkie1]

Important note: I've encountered circumstances in which Arc Pro will ignore a None transformation and silently pick the first one in it's list of what it thinks is appropriate when the tool is run. The way to verify if a transformation is applied or not is to look at the geoprocessing history in the metadata. (Tip: it’s easier to use the History panel than metadata, because it does the parsing for you.)

Using arcpy and manually specifiying no transformation seems to be reliable.

[MalcolmMeyer2]

My ortho imagery already being hosted on the web was exported without any transformation being applied, so all my data needs to match that imagery, until I upload new imagery. Still, QGIS also does not apply a transformation automatically between NAD83 and WGS84, and I utilize that in my workflow as well. This means I will likely not be using the new default transformation in ArcGIS Pro.

[MalcolmMeyer2]

I would be curious to know if HAZUS applied a transformation when converting their data to WGS84. In this article from March of this year it does not get into the details of the conversion.

Hazus input datasets, including state inventory data, were converted from NAD83 to the World Geodetic System 1984 (WGS84) coordinate system in order to better support U.S. territories and long-term goals for international hazard modeling.

https://www.fema.gov/media-library-data/1523565115955-4ba53dd63d9deb53f0bfeabb9ff240ed/Hazus_Coordin... 

If so, it would make me feel more comfortable in using the ITRF00 transformation.

[Anthonyde_la_Sota1]

Malcolm, review this  Procedure to project from NAD 1983 State Plane feet to WGS 1984 Web Mercator Auxiliary Sphere (Los Angeles County, CA):

When using the PROJECT utility, make sure to select the Geographic Transformation necessary to convert data between two geographic coordinate systems or datums. Select the Geographic Transformation NAD_1983_to_WGS_1984_5 or a more recent NAD_1983_to_WGS_1984_#

1.  Map Projection of Source Feature Class:

• NAD_1983_StatePlane_California_V_FIPS_0405_Feet
  • WKID: 2229 Authority: EPSG
• Projection: Lambert_Conformal_Conic
• • False_Easting: 6561666.666666666
  • False_Northing: 1640416.666666667
  • Central_Meridian: -118.0
  • Standard_Parallel_1: 34.03333333333333
  • Standard_Parallel_2: 35.46666666666667
  • Latitude_Of_Origin: 33.5
  • Linear Unit: Foot_US (0.3048006096012192)
• Geographic Coordinate System: GCS_North_American_1983
• • Angular Unit: Degree (0.0174532925199433)
  • Prime Meridian: Greenwich (0.0)
• Datum: D_North_American_1983
• •  Spheroid: GRS_1980
  •    Semimajor Axis: 6378137.0
  •    Semiminor Axis: 6356752.314140356
  •    Inverse Flattening: 298.257222101

2.  Map Projection of Target Feature Class:

• WGS_1984_Web_Mercator_Auxiliary_Sphere
  • WKID: 3857 Authority: EPSG
• Projection: Mercator_Auxiliary_Sphere
• • False_Easting: 0.0
  • False_Northing: 0.0
  • Central_Meridian: 0.0
  • Standard_Parallel_1: 0.0
  • Auxiliary_Sphere_Type: 0.0
  • Linear Unit: Meter (1.0)
• Geographic Coordinate System: GCS_WGS_1984
• • Angular Unit: Degree (0.0174532925199433)
  • Prime Meridian: Greenwich (0.0)
• Datum: D_WGS_1984
• •  Spheroid: WGS_1984
  •    Semimajor Axis: 6378137.0
  •    Semiminor Axis: 6356752.314245179
  •    Inverse Flattening: 298.257223563

>> Geographic Transformation:   NAD_1983_to_WGS_1984_5

RESULTS

[MalcolmMeyer2]

My original problem and question is more of a practical one than a technical one. Yes it seems that the most accurate way to convert between NAD83 and WGS84 is to use the ITRF00 transformation, as ArcGIS Pro does by default. However, when ArcMap and QGIS do not have this applied by default when using projection on-the-fly, it makes things very confusing. Additionally, it appears that when uploading data to Mapbox in NAD83, no transformation is applied. I would be curious to know if the same is true for data in NAD83 uploaded to ArcGIS Online, or again for the HAZUS data conversion.

-- Update 12/27/18 - HAZUS confirmed that they use the IRTF00 Transformation.

Since the data I am working with is not survey grade, I am going to stick with what is practical, which seems for the time being to disable transformations in ArcGIS Pro for NAD83-WGS84 until the industry as a whole adopts a standard.

-- Update 3/5/19 - I have not found a way to disable the default transformation in Model Builder in Pro.

[MelitaKennedy]

Sorry, late reply. Try setting NAD_1983_To_WGS_1984_1 via the environment (or the Project Tool) instead. It's basically a null transformation.

[JonathanPhoenix1]

Hi Melita, 

Would you mind to further explain what you mean when you say NAD_1983_To_WGS_1984_1 is "basically a null transformation"?  I'm trying to better understand the WGS84 to NAD83 process and you may being getting at something I was trying to confirm.