All mentioning of component geometry refer to the local coordinate system of the individual component. The axis convention is so that the \(z\) axis is along the neutron propagation axis, the \(y\) axis is vertical up, and the \(x\) axis points left when looking along the \(z\)-axis, completing a right-handed coordinate system. Most components ’position’ (as specified in the instrument description with the AT keyword) corresponds to their input side at the nominal beam position. However, a few components are radial and thus positioned in their centre.
Components are usually not designed to overlap. This may lead to loss of neutron rays. Warnings will be issued during simulation if sections of the instrument are not reached by any neutron rays, or if neutrons are removed. This is usually the sign of either overlapping components or a very low intensity.