How to control size of unit?

OpenGL OpenGL: Basic Coding
1

Hi,

I’m strugling from calculating exact size of
each unit in a world coordinates.
I have to maintain small size of unit in
order to draw an object and large size to
draw background image.
Usually, small size fits to meters and large
size to kilometers.
And also I’d like to calculate how large
a pixel takes.

Please, anybody help me !!!
(Refer to Developer’s FAQ 9.010)

2

numpixels = boundingSphereRadius / zDistance;
numpixels *= numpixels;
numpixels *= (screenHeight * screenWidth);

this’ll give u an approximation
boundingSphereRadius & zDistance refer to the object u wanna test

3

Thanks, ZED !

The information you posted helps me a lot,
however, I want to get a piece of code that
shows how to control size of unit.
Would you ?