Field Maps and Location Profiles - advice on workflow

[TanithLives]

G’day

This is regarding how Field Maps collects data and the need for Location Profiles. Just wondering if the community can help me shed some light on what is going on behind the scenes with my Field Maps data collection and whether I need to improve some steps.

My workflow at the moment is:

1/ A Field Map is made based upon GDA 2020 Feature Layers

2/ The underlying Web Map is edited to include an offline-capable basemap (in this case ‘World Imagery (for Export)’). From what I understand this reverts the Web Map to WGS 84

3/ At the moment (as we are testing) data in Field Maps is then collected using an integrated provider (phone), which I presume is collecting in WGS 84

We are about to move to network-corrected RTK, which will be collecting in GDA2020

My question is, is the current workflow resulting in some messy transformations that is negating the whole point of working in GDA2020 (accuracy)? When we move to the RTK, should I set up a Location Profile that transforms the GDA2020 from the receiver, to the WGS84 Web Map? Should I actually upload my own basemaps to ensure that the Web Map is not running in WGS84?

Any help is appreciated

[ChristopherCounsell · Accepted solution]

There can be three datum transformations.

• GPS (location profile) <1> Map <2> Layer <3> Database (if ArcGIS Server referenced)

The best thing you can do is have GDA2020 throughout all of this. External GPS with location profile, map with a GDA2020 basemap, layer published to GDA2020, and a source feature class in GDA2020 if publishing from an enterprise geodatabase.

<1> Using a web mercator Esri basemap and web mercator hosted feature layer, with a GDA2020 location profile is also fine. A datum transformation will be applied based on the profile. You can also use grid-based transformations here.

You will just want to ensure that:

• You use the GPS location, and not manually position the point on the map. Users may be tempted to do this as it's in the 'wrong' location relative to the basemap, but the basemap is inaccurate
• Enable GPS metadata on the layer
• Record what transformations are applied, and use the same transformation paths to/from i.e. when projecting back to GDA2020.

<2> If your map is in Web Mercator and your layer GDA2020 either :

• A default transformation will be applied
• A custom transformation will be applied. This is set at the time of publish from ArcGIS Pro based on the map settings. Grid-based transformations are not supported for GDA2020 in ArcGIS Online.

A while ago I wrote a series of articles on the above. Some of it is a little dated as new transformations are released however it will be a useful read for the ArcGIS Pro publishing behaviours.

https://esriaustraliatechblog.wordpress.com/2021/03/31/understanding-spatial-references-in-australia...

...extra three blogs at the end.

However, if you're using a phone gps, they're not super accurate anyway, so I personally wouldn't worry. I'd just set everything to WGS84 and accept that the data will be inaccurate based on the low quality GPS or referencing a basemap layer. The only misalignment issues you'll get will be if you mix GDA94 and GDA2020 data, noting that all WGS84 data will likely be aligned to 94 OR 2020 (don't think of WGS84 as a third coordinate system, just a null representation of 94 or 2020).

[TanithLives]

G'day @ChristopherCounsell. Thanks for the detailed response - I have indeed used your blogs before, as they are very helpful for the Aus setting. From the sounds of it, I am on the right track with the workflow and nothing catastrophic is happening in the background. Cheers.