// Constructor from just gravity magnitude; use negative of System "up"
// direction as the down direction here.
GravityImpl(const SimbodyMatterSubsystem& matter,
Real magnitude,
Real zeroHeight)
: matter(matter)
{ // Invoke the general constructor using system up direction.
new (this) GravityImpl(matter, -matter.getSystem().getUpDirection(),
magnitude, zeroHeight);
}
// Constructor from a gravity vector, which might have zero magnitude.
// In that case we'll negate the default up direction in the System as the
// default direction. That would only be noticeable if the magnitude were
// later increased without giving a new direction.
GravityImpl(const SimbodyMatterSubsystem& matter,
const Vec3& gravityVec,
Real zeroHeight)
: matter(matter)
{ // Invoke the general constructor using system up direction.
new (this) GravityImpl(matter, -matter.getSystem().getUpDirection(),
gravityVec.norm(), zeroHeight);
if (defMagnitude > 0)
defDirection=UnitVec3(gravityVec/defMagnitude,true);
}
