Hello Xander:
Thank you for posting this! I am wondering why my conversions are not lining up with my coordinates calculated in Arcmap. Is this the limit of this method as it is already less than 1 metre or do i need to set my Origin Shift differently perhaps?
X Conversion:
var originShift = 2.0 * PI * 6378137.0 / 2.0;
var lon = (Geometry($feature).x / originShift) * 180.0;
return [lon];
Y Conversion:
var originShift = 2.0 * PI * 6378137.0 / 2.0;
var lat = (Geometry($feature).y / originShift) * 180.0;
lat = 180.0 / PI * (2.0 * Atan( Exp( lat * PI / 180.0)) - PI / 2.0);
return [lat];
Kind Regards