All:
I have been experiencing the same issues described in this thread: trying to create an attribute expression that calculates lat/long coordinates from a hosted feature layer, then integrate Field Maps with Survey123 to open a form and have the geopoint plot the submitted survey on top of the feature using the result of the attribute expression using a custom URL via the custom URL popup (¢er=).
I have been using the "Expression/expr2 - Code to calculate geometry" formula called out in this post (and a multitude of others on the community page) and it was correctly calculating the coordinates in ArcGIS Online Web Viewer Classic, but then when we tested this functionality in the field, the point was not mapping.
I found that the original formula in the "Expression/expr2 - Code to calculate geometry" results in an Array data type, with associated brackets. These brackets do not show up in ArcGIS Online, but when you view the popup in Field Maps, you can see the brackets. So because of this, i tested further and in the original function, i removed the brackets in the result line, which worked but was not perfect. It was not perfect because the coordinate results ended up being truncated to 2 decimals, and even though the submitted form was executing, the point was being plotted hundred of feet away.
After 10 hours of testing and researching these threads (which by the way, all of the contributions are EXPONENTIALLY HELPFUL AND I AM SO GRATEFUL OF YOUR KNOWLEDGE) i was able to find the CORRECT SOLUTION:
1.) Create an attribute expression for latitude:
var lat;
var originShift = 2.0 * PI * 6378137.0 / 2.0;
lat = number(Geometry($feature).y / originShift) * 180.0;
lat = 180.0 / PI * (2.0 * Atan( Exp( lat * PI / 180.0)) - PI / 2.0);
return lat;
2.) Create an attribute expression for longitude:
var lon;
var originShift = 2.0 * PI * 6378137.0 / 2.0;
lon = number(Geometry($feature).x / originShift) * 180.0;
return lon;
3.) Because of the "number" identifier, In ArcGIS Online Web Map Viewer Classic go to Configure Popups, make sure your pop up display is custom, then the important step is to click Configure Attributes. Navigate to the newly created expressions and expand the decimal places to a minimum of 5.
4.) Lastly, in the custom URL make the "¢er={expression/expr3},{expression/expr4} where expr 3 is Lat and expr 4 is Long.
I have been testing since i discovered this and it has been running smoothly. Happy Mapping!