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Coordinate Systems for Web Map and Data to use in Field Maps

GISUSER6

Hello. If I wanted to collect data in a local coordinate system (CS), would I create my data in the local CS and create a custom basemap in that same CS? I am using a Trimble DA2 reiciever to collect data. For the location profile in Field Maps, would I always chose NAD 1983 2011 as my GNSS CS and then the local CS as my map CS?

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ColinLawrence

Hi @GISUSER6 , there are slight amounts of error introduced for each transformation so in an ideal situation you would avoid transformations where possible. If you create and publish your data in NAD83 2011, and your basemap is also in NAD83 2011, and you are receiving locations from your Trimble in the same coordinate system as well, then there is no need for a transformation. You will still want to set up a Location Profile defining the CS of your Map (basemap) and locations coming from your receiver. Are you using a correction service with the DA2 that is outputting locations in NAD83 2011?

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ahmedkabeer

Hello BillFox,

i need orthometric height in my point feature collecting field maps connected with rtk GPS, pls help to figure out

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ColinLawrence

With this data in the local county coordinate system already, it seems to make more sense to stick with set up #1. Is my thought process off on this?

I agree with this; I believe you are on the right track. I cant comment too much on the Z value results though as I have less experience in the area of vertical datums.

GISUSER6

I did some more testing.

Set up #1:

Using the custom basemap in the local county coordinate system, then publishing the hosted feature service in that same local county coordinate system. The GNSS input is always NAD 1983 (2011).

Transformation is NAD_1983_HARN_To_NAD_1983_2011 in Esri Field Maps.

Set up #2:

Data, custom basemap, and GNSS output is all in NAD 1983 (2011).

No transformation is occurring in field maps, but then post-processing of the data occurs by projecting the data to the local county coordinate system in ArcGIS Pro.

I tested on two devices with varying accuracy levels. One was an Eos Arrow Gold CM Receiver. I actually ended up having more accurate results with the Set Up #1 with the hosted feature service being in the local county coordinate system than it being in NAD 1983 (2011) for Z values. X and Y were pretty comparable. With this data in the local county coordinate system already, it seems to make more sense to stick with set up #1. Is my thought process off on this?

GISUSER6

I am using the ArcGIS Pro GPS metadata tool which saves the Z to an altitude in meters. Additionally, I am using an arcade expression to get the orthometric height in feet which is the final z value I want stored.

var feature = $feature;

if (feature != null && Geometry(feature) != null) {

var Z = Geometry(feature).Z;

return Round (Z*3.28084, 3);

}

else {

return "Error";

}

BillFox

for z, are you wanting meters or feet? ortho-metric or ellipsoidal height?

GISUSER6

Okay. The correct transformation is available. From what I understand the bottom line is that the data uploaded to ArcGIS Online should be in whatever coordinate system the GNSS reciever is recieving corrections from? Regardless of the basemap used, whether that basemap coordinate system be NAD 1983 (2011) or my local coordindate system?

ColinLawrence

It would depend on what the local coordinate system is and if there is a transformation available between that and NAD83 2011. I cannot speak on the specifics in this case but you have the right idea. If its not available for some reason, you would have to perform the final transformation after the fact as you mentioned before.

GISUSER6

Thank you for the input.

Eventually I'd like to have the custom basemaps be in the local coordinate system for viewing the data and maps. Let's say field workers want to view the data in Field Maps. Would the data at this point need to be in the local coordinate system and I would need to set a location profile for GNSS to be NAD 1983 2011 to my map coordinate system as the local map coordinate system?

ColinLawrence

You will still need to set the Location Profile the way you mentioned even though there is no transformation needed. If there is no Profile Field Maps will assume coordinates are received in WGS 84. Even though a transformation is needed down the road for you it will still be good practice to remove unnecessary transformations during the collection process.

GISUSER6

Hi Colin,

Thanks for the input. Yes, we are using a catalyst subscription that comes with RTX corrections which is in Nad 1983 (2011). If the basemap, data uploaded, and locations coming in from the reciever are all NAD (1983) 2011, then the location profile would have to be set up as NAD 1983 (2011) to NAD 1983 (2011). No transformation involved as you said. When I added the location profile as such, it does allow me to create the profile but just notes that there is no transformation available.

Another note: When the data is exported, our final CS is to be in that local coordinate system anyway so there will still be a post-processing transformation if the all of the data, basemaps, and locations from the reciever are in NAD 1983 (2011).

ColinLawrence

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