Hi All,
I’m wondering in which coordinates system, vertices of GLTF objects should be expressed.
The context is the following : I start from GIS files containing buildings outlines, generally projected into UTM/WGS84, with meters coordinates;
each contour has two attributes absolute elevation and height.
I can easily convert from X/Y to Lon/Lat WGS84 in degrees or radians.
I’m able to create Gltf files containing extruded polygons.
The goal is then to place them on earth at the right place.
My question is :

in which coordinates system should model vertices be expressed ? lon/lat/height over ellipsoid ? lon/lat/Z ? metric with a top node to place them at the right place ?

generally model are placed onto the globe with something like :
var modelMatrix = Cesium.Transforms.eastNorthUpToFixedFrame(
Cesium.Cartesian3.fromDegrees(75.62898254394531, 40.02804946899414, 0.0));
var model = scene.primitives.add(Cesium.Model.fromGltf({
url : ‘http://luxcarta.net/3dportal/data/un2.gltf’,
modelMatrix : modelMatrix,
scale : 1.0
In my case, models are already placed  which matrix should I use ? identify ? None ?
I’m quite new to Cesium and GLTF, any hints / links are appreciated.
Thalks in advance,
Fred.