Bridges (and tunnels)

  • To build bridges and tunnels in LOTUS you have to use the parameter "Layer". This parameter tells LOTUS in which "floor" the object, the spline or subgrade is in. In this article we describe the work with layers and build a simple bridge.

    1 Theory

    Every element, a spline, an object, a railtrack or a subgrade, has a parameter called "Layer". This is value, that could be a positive or negative number.

    1.1 "Floors"

    You can imagine these layers like floors of a building. Everything that is based on the ground (and the terrain itself) has the value 0. This is also the default setting. Values below zero are the basement, like tunnels; but they are currently not supported.. In conclusion a value above zero is a bridge.


    Important: This does not mean, that a route or a road on a embankment or an indentation should have a value differing to zero. These roads or routes remain on layer 0. The route you are driving on is basically layer 0 and the other travel routes depending on the situation have different value than your route.

    1.2 Seperating two layers

    Two layers that cross each other should always have a difference of two. So if you have a street on the ground (layer 0), the bridge above the street has layer 2.


    The reason behind this is the following: At the occasion, where the layer changes its value, the splines and polygons have to have an effect on each other even if they are not on the same layer. To ensure this effect splines and polygons (and other types of objects of course) affect each other when the difference between two layer is at a maximum of 1.

    2 Layers in the Map Editor

    2.1 Assign a layer

    At first the parameter "Layer" is a usual parameter for objects and so on. To ease the work with layer you can set the "Layer" in the Map Editor within the menu bar "Gen. construction" for further use or set the parameter for currently selected objects.

    2.2 Subgrades

    For manipulating the height of the terrain within the several layers you use subgrades. When working with splines or polygons the height and the shape get vertical adjusted depending on the layer setting, which is currently used. If there is no subgrade at this point, the next lower layer will be chosen until the layer 0 is used.


    Because of the enormous importance of subgrades they get different colors when using different layer settings. The layer 0 remains lightgray, layer 1 appears yellow, layer 2 is red, layer 3 shines blue, layer 4 has the color green and so on.

    2.3 Refresh

    The terrain refresh is working concerning to layer "relatively manually", especially it refreshes only on one layer. So there are the following rules:

    • The "manual full refresh" :refreshmt: is working on the layer which is set in the menu bar at "Gen construction"!
    • The "automatic refresh" :refresh: and the "refresh of certain objects" ("red triangle") are working on the layer which the object is situated on!

    In conclusion: When working at transition of two layers you have to manually refresh on several layers. Especially when you spot holes in the terrain, please check if every layer is refreshed!

    3 Building a bridge - step by step

    We close this article with a step by step manual to build a simple bridge.


    We recommend to turn off the automatic terrain refresh and refresh manually.

    3.1 Subgrades

    At first we build the subgrades for the embankment and the bridge. In this case we chose a height of 8 meters, the normal terrain is on 0 meters:



    The transition elements are on layer 1, so they appear yellow. The middle part is on layer 2, so the terrain is aligned to the outer subgrade. Keep in mind, that the width of the subgrades should be as big as the whole bridge including railtracks, streets, sidewalks and railings.


    Normally it won't be that easy with the terrain on 0 meters, so you have to use a subgrades on the layer 0.


    This constellation shows a behavior, which is basically used, but in this case the subgrade don't affect each other:



    In this case the lower subgrade affects the upper subgrade. To disable this effect you turn off the option "Smooth transition to neighbor subgrades of higher priority". The result lokks like this:


    3.2 Building the street under the bridge

    The building of the street isn't that special, because the subgrades of the upper layers have no effect on the height of the splines and polygons concerning to the street. It is important to ensure you set layer 0 before building the street.



    You have to refresh on layer 0 with the button :refreshmt: .

    3.3 Building the upper street

    When building the transition between two layers you have to keep an eye on:

    • A polygon or a spline, which is located on two subgrades with a different layer, should always have the higher layer value
    • The difference between two connected polygons or spline shouldn't be higher as 1.

    The order for building the splines or polygons of a bridge is not set, for a better understanding we build in this case from the inside to the outside starting with the bridge itself. The first step is to set the layer on 2. The other functions like Z-value or Priority working like before. After placing splines and polygons the layer setting remains on 2 and you can click on :refreshmt::



    Important: The splines and polygons on layer 2 should cross the subgrades of the layer 1, but not the other way around.


    Now we build the bridgehead. The method remains the same. Set the layer on the value 1, build the splines from layer 1 a little bit on the layer 0 and refresh the layer 1 with :refreshmt::



    Und ebenso wird dann auch der Rest auf Ebene 0 gebaut:

    You know what to do when building on layer 0 ;):



    Done! :-)

    3.4 Superstructure of the bridge

    The superstructure of the bridge should be imported as a normal spline, where the Z-value of the sidewalk should be zero. The spline of the bridge should be on layer 2 to follow the the already built terrain elements (sidewalk, rail, street).