Position information in las file calculation

Hello Team,
I have a observation with uploading a point cloud data on the ion that I would like to share.

I have a las file with no position (EPSG) information in it and when I upload it on the ion it get’s uploaded on some random location.

Next, I update the horizontal position information (Horizontal EPSG) to the las file and I upload it, it get’s tiled at correct location but it is buried inside the ground.

Next, I update the file with vertical EPSG upload it, it is getting placed at correct location and on the surface of earth and not buried inside.

I want to understand the last step, with the vertical EPSG in the file.
Que 1) How cesium is getting this vertical height shift ?

Que 2) Also when I upload the las file with only horizontal information (Horizontal EPSG) where it is getting placed in the following figure ?

is it on ellipsoid or on geoid ? definitely not topographic surface because it is buried in ground.

Looking for answers.
Thank you.

Hi there,

You might get a better response over in the Cesium ion category, as it’s more tailored to ion and to user data.