Trainz/Overview of Attachment Points
Attachment points are created in the 3D modelling software used to create an asset which results in a mesh file, and the process often also generates support files such as textures—both image files per se, and processing instructions in the texture.txt files. Those of course are most visible and most frequently seen as they predominate most large assets open for editing. None have any purpose though without a mesh, and there are few meshes that don't incorporate attachment points of one sort or another. Quite a few resources in Trainz have more than one mesh file required to render, so it is not uncommon to see an asset specify an invisible mesh whose purpose is to act as an origin to which every other mesh and the game surfaces are registered. That simple triangle or square that is all but invisible through a mesh viewing tool (e.g. PEV's Mesh Viewer2.exe) and never seen in game run-time modules none-the-less serves a important purpose as a reference and placement 'handle'. In one sense, the main model in such cases is the model of an invisible handle, but one which can be put into the virtual world and moved about
The real purpose of this sort of mesh is to provide adjustable and repositionable attachment points relative to that origin, which is adjustable within limits inside the asset config.txt file. In the event, fine fractions of a centimeter tweaking can be easily accommodated by the asset creator, making variations of a invisible mesh— and that can be done quite quickly, a fact important to the Steam Engine or Modern Deisel modeler who likely spent 6-8 months putting together the many parts of such locomotives.
The attachment points purpose is to specify the exact coordinates where one asset item/sub-mesh/effect connects to another, for example, where the track connects onto a bridge, or where the cab is placed inside a locomotive. All attachment points are referenced in the config.txt file of an asset to define its use and function.
Attachment points must follow strict naming conventions provided in the Content Creation Guide for their implementation in Trainz. In 3DS Max and Gmax, attachment points should always be placed in top view with for the orientation of the axis to be correct. They may then be rotated if needed. If creating a Locomotive, the train should be facing down the page in top view.
Commonly Used Attachment Points on Locomotives Edit
a.limfront: front of train
a.limback: rear of train
a.bog0: front bogey
a.bog1: back bogey
a.bogx: any other bogey
a.cabfront: front cab
a.cabback: rear cab
a.outsideviewx: external cameras
a.whistle: whistle/horn particle effect
a.sitpointx: sitting passenger
a.standpointx: standing passenger