Northwestern shift in Collector when using SBAS with R2

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01-08-2018 05:13 AM
JohnSmith40
New Contributor III

Hello,

We have recently switched to collecting our GPS data using an R2 unit and Collector. Here in Florida we are lucky enough to have free RTK corrections through the Florida Permanent Reference Network. The vast majority of the time this correction service is up and running. However, sometimes it is down and we have to use SBAS to collect our data. I’ve noticed a consistent shift in a northwestern direction from our assets when collecting data using SBAS. I’m wondering what the proper location profile is for using SBAS?

So far I have tried the default location profile, as well as two additional location profiles (screenshots attached). All of these location profiles produce a similar result (northwestern shift of the data).

Any possible solutions would be greatly appreciated. Thank you for your time.

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4 Replies
by Anonymous User
Not applicable

John,

Are you using a basemap that uses the same projection as the coordinate system being used by the GPS?

Use high-accuracy GPS—Collector for ArcGIS | ArcGIS 

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JohnSmith40
New Contributor III

I am using the default Esri basemap, I believe. I only have the feature class I use to collect data published as a feature service.

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JayRiester1
New Contributor III

John,

Hi, by default your State or Private RTK/VRS is most likely using a NAD 83 2011 Datum. Double check with them to be 100% sure. SBAS/WAAS on the other hand uses a WGS84 Datum.

In the lower 48 states there is an "Approximate" 1 meter shift between these 2 Datums.  The "shift" should be consistent which is much easier to fix than if the GPS data was not in a consistent shifted direction.

So this is why you are seeing a shift when using these 2 Different Correction Sources with 2 different datums.  I use the term "Apples to Pineapples" when if comes to different datums. They sound similar but they are not the same.

There are derived from 2 different mathematical equations and starting references.

WGS84 is Lat/Long and HAE for its elevation on a global scale.  NAD83 datums are using Northern/Easting and MSL with a current Geoid for its Elevation.

See these articles for more information on WGS84 vs NAD 1983:

Recently posted to LinkedIn:

https://www.linkedin.com/pulse/wgs84-nad83-does-matter-david-carter/

Posted to Esri Blog August 2010:

https://blogs.esri.com/esri/arcgis/2010/08/12/wgs84-vs-nad83/

You can also prove this datum shift with your GPS unit on Known NGS Control.  I like to use the following NGS website to look up NGS Control Data Sheets as it has an interactive map: https://www.ngs.noaa.gov/NGSDataExplorer/

Thanks,

Jay

JohnSmith40
New Contributor III

Thanks for the great information Jay

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