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RTK Streams with Reference Frame ITRF 2014 Unable to handle On-the-Fly Projection/Transformation in Field Maps

GeobilityCo

I've been using and helping others configure and utilize RTK corrections from various services in Idaho, Oregon, and Florida. A couple of the major RTK service providers have switched from NAD83(2011) to ITRF 2014 with a specific Epoch as their reference frame. This is a time-dependent reference frame that accounts for the shift in tectonic plates over time (as I understand it). That's truly amazing for improving the accuracy of located features. However, I work for local government, and small businesses and non-profits. They all need to use local projected coordinate systems that match county or state data. The method of transforming from ITRF 2014, according to National Geodetic Survey (NGS), to other reference frames is complex and requires that time be one of the variables needed in calculating the transformation. NGS provides a tool called Horizontal Time-Dependent Positioning (HTDP). However, the beauty of ArcGIS Field Maps and RTK was to collect high-accuracy locations without post-processing. There are no on-the-fly transformations available in Field Maps from ITRF 2014 to anything without it being locked to a specific epoch that isn't necessarily what the RTK provider uses. With the switch in the RTK providers reference frame, we could publish intermediate layers in ITRF 2014 to collect in so we don't have to transform on-the-fly at all. But, we are now going back to post processing data, in a way. Also, I don't know of how to apply a time-dependent transformation from ITRF 2014 within the ESRI ecosystem. I have to resort to custom python code to transform and project. I was getting within an inch or two when shooting known points as a control. Now, I'm nearly a foot off. Anyone else trying to figure this out or have a solution?

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JonathanLebowitz

Hi @GeobilityCo Time-dependent transformations are not currently supported in Esri products. If your project requires that level of accuracy, you will need to create a custom transformation to bring your data from ITRF 2014 at the collection epoch to NAD 83 (2011) at Epoch 2010.0. We have the ITRF 2014 To NAD83 2011 At Epoch 2010.0 FE/WKID 108379 transformation available out-of-the-box, which is based on the transformation parameters documented at https://epsg.org/transformation_8970/ITRF2014-to-NAD83-2011-1.html . Velocity parameters are also published there that can be used to create the custom Coordinate Frame transformation; the workflow for building the transformation is documented at https://epsg.org/coord-operation-method_1056/Time-dependent-Coordinate-Frame-rotation-geocen.html . Alternatively, can you configure your corrections service provider/GNSS receiver to provide coordinate values in GCS NAD 83 (2011)?

GeobilityCo

Thank you for the info @JonathanLebowitz. I'll see if I can figure out those velocity parameters. Just so I understand correctly, generating this custom transformation file will work for post-processing in ArcPy or ArcGIS Pro. Still not going to work for Field Maps, correct?

About my corrections service provider, I don't have the ability to change their reference frame. However, after reaching out to them, they indicated they are working on an upgrade that would allow us to append something to the end of our Mount Point (maybe a WKID or something) that specifies which reference system we would like to receive corrections in. That will help. It's 6 months to a year away though.

I did create a profile in ArcGIS Field Maps that treats the incoming corrections as if they were ITRF 2014 (epoch 2010) and the map coordinate system to our local projection. That is how I was able to get on-the-fly transformations to within 1 ft of known control points. After post-processing these with NGS Helmert and HDTP, we are back to within 1 inch (actually down to 0.6 inches) horizontal.

JonathanLebowitz

Hi @GeobilityCo There is not currently a way to create or upload/use custom transformations in ArcGIS Field Maps, only in ArcGIS Pro. What is the coordinate system of the feature layer? Is it different than the map coordinate system? Field Maps won't recognize to use the out-of-the-box ITRF 2014 To NAD83 2011 At Epoch 2010.0 FE/WKID 108379 transformation unless the input data is in ITRF 2014 Epoch 2010.0/WKID 9000. What is the reference epoch reported by the corrections service?

GeobilityCo

That's exactly what I encountered. From Earthscope:

All raw data streams use the ITRF2014 reference frame. For NOTA stations, the epoch date is 2026-03-30. For non-NOTA stations, positions in the stream are best estimates and do not include a precise epoch date.

We were using a NOTA station. So the epoch we need is 3/30/2026. I don't think there is a coordinate system in the ESRI software suite that uses that epoch for ITRF 2014. At this point, my plan is just to use ESRI's WKID 9000 for ITRF 2014 and then programmatically use a helmert transformation to transform the values from the ESRIGNSS metadata fields to create points to the 2010 epoch so that I can use standard project geoprocessing tools from there. Not sure if that will properly transform the elevation values though.

Any recommendations?

JonathanLebowitz

Which vertical coordinate system are your elevation values in? The ITRF 2014 To NAD83 2011 At Epoch 2010.0 FE transformation would only impact ellipsoidal heights. Orthometric heights would have to handled separately.

GeobilityCo

As I understand it, the ESRIGNSS_ALTITUDE field should contain ellipsoid height in ITRF 2014 (epoch 2026). Since I am programmatically creating the point features from the metadata fields, I can put that as the Z value. I would like to end up with pointZ being an orthometric height in NAVD88 USFT. However, if that is problematic, I can live with Z values in ellipsoidal height in whatever ESRI can produce, as long as I have a method to calculate a field to orthometric NAVD88 USFT.

Thanks so much for your help.

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