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Collector for ArcGIS - High Accuracy Receiver and Default Location Profile

Question asked by NorthBay on Aug 1, 2018

Background Understanding;

Our AGOL Feature Layer is in NAD83 Zone 17 CSRS (epsg:2958) as well as our correction service (NTRIP) is provided using a Trimble R2. I am assuming that Collector and all AGOL webmaps are in the SRS Web Mercator (epsg:3857)

We also know datum Transformations introduce error.

In Canada, certain Datum Transformation regarding NAD83 Zone 17 CSRS (epsg:2958) are unavailable in Collector (as I understand it, due to IP rights of some organization) so that leaves me using a Default Location Profile in Collector. So what is exactly happening? Is the value of having the high-accurate GNSS connected diminished?

My Question(s);

My end goal is to build a SQL point database with the GIS accuracy (7cm-30cm) in the NAD83 Zone 17 CSRS (epsg:2958) system. When I export my AGOL Feature Layer to shape/GDB I see that the .prj is still in NAD83 Zone 17 CSRS (epsg:2958). Can I assume the 7cm accuracy is maintained through this download process (R2 with Corrections > Collector > AGOL > Export > GDB)?

Also, the data collectors will be using Collector to navigate back to a location in an emergency valve shut-off scenario.

I understand that placing the Collected Data on an AGOL webmap may have an undesirable shift (due to a default location profile), as even the best transformation model will introduce centimetres or metres of error. Therefore, isn’t the 7cm-30cm just washed away during a transformation onto a webmap? As an example: NAD83_1983_To_WGS_1984_1 provides 4m of accuracy (https://support.esri.com/en/technical-article/000005929)

So I suppose my questions in a nutshell would be;

  1. In my process of using a Default Location Provider - is there any accuracy degradation happening to my AGOL Feature Layer? (After all when using Default I am telling collector the corrections are in WGS84)
  2. If I did have a Location Profile setup and the datum transformation is applied to the AGOL Feature Layer onto the webmap, does this affect the core AGOL Feature Layer dataset and its accuracy? (We know it does not in Desktop as it is an on-the-fly projection)
  3. Can I estimate any introduced error of the AGOL dataset on the webmap in order to provide guidance to our staff.

I plan on observing a few benchmarks to know for sure but am looking for a bit of explanation on this from the pros.

Thanks for anything you can offer.

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