how to convert as accurately as possible (mm precision) from X Y coordinates and elevation to longitude and latitude.

With the earthlanchorpoint function or in the options I have no choice

this will allow me to export in ifc with the correct geolocation

90° = 10^4 km = 10^10 mm

You cannot specify the Earth Anchor Point in mm or meters, because it represents *a point on the physical globe* — or more specifically, a relationship between your perfectly straight XYZ coordinate system and a real position in space. Where on earth is “20m, 50m”?

IFC’s geolocation is the same thing, albeit a bit more complicated. It is a mapping between the model’s XYZ coordinates and a real point in the world, utilizing a CRS (coordinate reference system) which defines such a mapping.

Only *after* you have established a mapping (and a projection) between a latitude/longitude and a model location (typically 0,0,0), can you then convert between lat/lon values and meters.

You’ll also need to understand State Plane coordinates and adjust your model accordingly, but here is a link to a converter:

THANKS BUT I’M IN FRENCH

we you lambert 93

i know the differency between sphere coordinate and plan like UTM

but coordinate in lambert 93 or lambert 2 is not exactly the same

can you give me an exemple, if i’m in french we use lambert 93 or lambert 2

and i have NS xxxx meters and OE xxxx meters

You’ll have to use a converter to go from Lambert to Lat Lon: