I have a local ENU coordinate system on the surface of the Earth (similar to this question: GPS coordinates to XYZ on relative grid). I know the lat,lon,alt of the local ENU origin, and thus I can also get the origin in terms of ECEF.
Now, I have a point of interest that I'd like to know its ECEF XYZ coordinates. I don't know the lat/lon/alt of the POI, but I do know its position relative to my local ENU grid/origin. How can I calculate the ECEF XYZ coordinates of my POI? An alternative approach might be to first get the lat/lon/alt of the POI.
I tried using this formula (https://gssc.esa.int/navipedia/index.php/Transformations_between_ECEF_and_ENU_coordinates) to convert ENU to ECEF, but it's not really working. It's obvious that the formula has no consideration for the fact that the ENU origin has an altitude. I tried applying some earth radius distance to the "U", and that can get me close to the correct answer, but it looks like this also changes the latitude, so I assume I'm using an incorrect approach.