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When using SBAS with the ESRI default coordinate system of WGS 1984 Web Mercator Auxiliary Sphere in Field Maps, which geoid should be used in TMM?

Will that have any affect on the horizontal positions? 

Thanks for any help.

When using SBAS with the ESRI default coordinate system of WGS 1984 Web Mercator Auxiliary Sphere in Field Maps, which geoid should be used in TMM?

Will that have any affect on the horizontal positions? 

Thanks for any help.

Hi Paul. Technically, GEOID18 (CONUS) as an implementation of the NAVD88 vertical datum is only supposed to be used with NAD 1983 (2011) as the horizontal datum. If you use it with WGS84 as the horizontal datum, your Z values will be incorrect by the difference in height between the two reference ellipsoids (GRS80 vs WGS84) at that location...which in some cases could be a bigger source of error than the inheritent limitations of SBAS as a correction source. Probably what I'd do in this case is configure TMM to output "Auto" which will be NAD 1983 (2011) and then pick the GEOID18 (CONUS) option for orthometric heights. Then in Field Maps, I'd setup a location profile and set the incoming GNSS as GCS NAD 1983 2011 (EPSG:6318) and the map coordinate system as WGS84 Web Merc Aux Sphere (EPSG:3857)...with the first transformation selected from the list (using the ITRF08 parameters). That would at least give you correct Z values within the limitations of SBAS accuracy.

https://geospatial.trimble.com/en/resources/blog/best-practice-for-using-trimble-gnss-receivers-with-esri-arcgis-field-maps

When using SBAS with the ESRI default coordinate system of WGS 1984 Web Mercator Auxiliary Sphere in Field Maps, which geoid should be used in TMM?

Will that have any affect on the horizontal positions? 

Thanks for any help.

@Jamie Maxwell - thank you.

@Matthew Morris:

Thank you.

I stepped through the settings in the TMM Configuration page but there must be some differences. Is that what you mean:

GNSS correction source = Auto (SBAS in our case)

Output = Select from list

GNSS output = NAD83(2011) (EPOCH:2010)

Geoid = GEOID18(Conus)

Field Maps Location Profile:

I am curious - is there not a setting for the geoid of the input source (SBAS in my case)? Would that be something like EGM96 or ITRF2014? Especially when the source could be RTX or SBAS?

Hi Paul. Technically, GEOID18 (CONUS) as an implementation of the NAVD88 vertical datum is only supposed to be used with NAD 1983 (2011) as the horizontal datum. If you use it with WGS84 as the horizontal datum, your Z values will be incorrect by the difference in height between the two reference ellipsoids (GRS80 vs WGS84) at that location...which in some cases could be a bigger source of error than the inheritent limitations of SBAS as a correction source. Probably what I'd do in this case is configure TMM to output "Auto" which will be NAD 1983 (2011) and then pick the GEOID18 (CONUS) option for orthometric heights. Then in Field Maps, I'd setup a location profile and set the incoming GNSS as GCS NAD 1983 2011 (EPSG:6318) and the map coordinate system as WGS84 Web Merc Aux Sphere (EPSG:3857)...with the first transformation selected from the list (using the ITRF08 parameters). That would at least give you correct Z values within the limitations of SBAS accuracy.

https://geospatial.trimble.com/en/resources/blog/best-practice-for-using-trimble-gnss-receivers-with-esri-arcgis-field-maps

When using SBAS with the ESRI default coordinate system of WGS 1984 Web Mercator Auxiliary Sphere in Field Maps, which geoid should be used in TMM?

Will that have any affect on the horizontal positions? 

Thanks for any help.