Please read this link.
http://www.bulletphysics.org/mediawiki-1.5.8/index.php?title=Scaling_The_World
When I originally started using Bullet physics in my DBPro plugin DLL I had to deal with scale because the average size of objects
that were used by DBPro users( including me) was not with in the range of the Bullet physics solver.
Quoting the Bullet Documentation from the link above.
Quote: "By default, Bullet assumes units to be in meters and time in seconds. Moving objects are assumed to be in the range of 0.05 units, about the size of a pebble, to 10, the size of a truck. The simulation steps in fraction of seconds (1/60 sec or 60 hertz), and gravity in meters per square second (9.8 m/s^2). "
So if we want to use the default gravity of -10.0 m/s^2(Rounded) on the Y axis, an object say for example a FPSC character of 72 DBPro
units tall will not fall at a correct visual rate on screen because it's size is outside the Bullet physics solver range.
So I needed to calculate a scale factor to scale the objects size by to keep it with in the Bullet physics range.
As stated in the Bullet physics documentation: By default, Bullet assumes units to be in meters and time in seconds.
Moving objects are assumed to be in the range of 0.05 units, about the size of a pebble, to 10, the size of a truck. So 1.8 meters the average
size of a person times 40(scale factor) = 72 DBPro units. In my DBPro DLL I used the 40 scale factor to scale down the size of the DBPro objects
then pass that size to the Bullet physics engine. When Bullet gives me back the new position of the object I scale it back up to give the correct
position on screen for the best visual results. When I added Bullet to AppGameKit the character I was given to use for the demos was a FPSC masked
soldier which was also 72 AppGameKit units tall. So the 40 scale factor was still a good default scale at the default gravity. The AppGameKit user has the ability to
change the gravity and the scale factor to what ever works best for their projects. If you do not want to use the scale factor just set it to 1.
Then just keep the size of your objects with in the Bullet solver range.
In conclusion 40 is not an odd scale nor does it have anything to do what country it was created in.
FYI in the United States all scientific calculations(physics) are done using the metric system.
All the other physics engine solvers also work this way.
Hope this helps clarify the subject.
The coffee is lovely dark and deep,and I have code to write before I sleep.
