how to get screen pixel (xy) coordinate of a world object (xyz)?

[Horst JENS]

I need to calculate the exact screen coordinate (xy) of an 3d object (xyz). I need the distance from the center of the screen.

my camera axis always is vector(0,0,-1)

I understand that I can calculate

scene.pixel_to_world to get how many world units is one pixel at the xy-plane (going through the origin) has 

and i understand that i can calculate 1/scene.pixel_to_world to get how many pixel a world unit has in the same plane.

However i struggle to determine the distance in pixel from the screen center of any 3d objects with an x,y,z coordinate (with an z coordinate that is other than zero)

Is it possible to use the vector projection to project the position of the 3d object on the screen plane ?

[Bruce Sherwood]

Not sure this is relevant, but you could set scene.fov to a very small number such as 0.001.

And of course if ;your objects are boxes, you could make their thicknesses very small.

Basically, though, there is no way around the fact that VPython is all about 3D.

Bruce

[Bruce Sherwood]

I should add that you could restrict your objects to triangles or quads, since these are truly 2D.

    https://www.glowscript.org/docs/VPythonDocs/vertex.html

Bruce

[Horst JENS]

I do have 3d objects (cylinders etc.) and need to determine the pixel (xy) coordinate (x and y distance from the screen center)  of a given 3d object / 3d vector with an x,y,z coordinate. 

[Bruce Sherwood]

Note too that scene.width is the number of pixels in the width of the canvas and scene.height is the number of pixels in the height of the canvas.

I don't really understand what the problem is. Maybe you need to use some application other than VPython.

Bruce