From the WorldToScreen() scene method description on page 85 of the Poser 11 Poser Python Methods Manual it "Takes a set of (x, y, z) world coordinates (the location of a point within the 3D scene) and returns (x, y, z) screen coordinates (the location of that point relative to the screen)."

It's not clear to me what this method actually returns as "screen coordinates" are explicitly 2-dimensional (x, y) not 3-dimensional (x, y, z).

So is it

(a) just a transformation from world space to camera space, returning a true set of 3D coordinates.

(b) a calculation of the 2-dimensional x,y screen position plus the "Z-depth" 

---

The 3Dcheapskate* occasionally posts sensible stuff. Usually by accident.
And it usually uses Poser 11, with units set to inches. Except when it's using Poser 6 or PP2014, or when its units are set to PNU.

*also available in ShareCG, DAZ, and HiveWire3D flavours (the DeviantArt and CGBytes flavour have been discontinued).