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Bridges are a subset of Transit Networks and apply mainly to vehicular travel. Technically power lines can form a bridge (the model switches to show the yellow orbs) but for the present purposes of this article, only networks which move sims will be discussed. They are used by the game to traverse bodies of water, or even land if bridge is high enough. All of the standard game transit networks, with the exception of streets can create bridges. With developments in the NAM, it is now possible to create bridges for any transit network that is contained in the Bridge Controller file in the NAM.
A bridge is essentially composed of three pieces:
- A Start/End Piece (automatically reversed when drawn in game)
- A Support Piece (is what extends to the surface to support the bridge)
- A Repeat Piece (fills in the gaps between the Start/End and Support pieces)
Each bridge piece can be modelled in the BAT and must be rendered with a specifc and unique ID. The exemplar that is attached to the model will define what type of bridge it will be used with. A tutorial for the creation of basic, three piece bridges can be found at SC4Devotion. The creation of more complex bridges, like suspension bridges, involves the use of RULs.
The LODs (Level Of Detail) for the bridge may be as wide as necessary, but may only be 16m (one game tile) long. They should be rendered with xy coordinates of 0,0. If the LOD covers the roadbed, it will obscure the vehicles using the bridge so care must be taken when designing bridges with parts above the roadbed. A bridge that wishes to include sections longer than 16m must break the section into 16m segements. For example: if you have a Start/End piece that is 32m long, it must be rendered as two separate 16m long models, each with its own ID. They will then be modded as Start/End pieces in the Reader
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