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Floating extrusion bridge

arno

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Hi all,

I'm playing around with XML extrusion bridges a bit, but I have a problem. I put the first and last point of the bridge below ground level to make sure the road connects nicely with the terrain. But if I increase the height of the bridge these last points start to pop up above the terrain. Even if I put the last point lower they sometimes still show above the ground.

Has anybody seen this before and what is the solution for this?
 

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HolgerSandmann

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Hi Arno,

indeed, extrusion bridges are tricky to get right; the altitude above ground at the end points doesn't only change when you adjust the values of inner pylons but also when adding or removing pylon points later on.

SBuilderX works around the issue of the "dangling" end sections by automatically adding another point at each end with altitude="-20M". Since I mostly place extrusion bridges with SBX I have, over time, come up with my own list of pylon values that work for most cases, e.g., a standard 4-point bridge gets altitude values of 3.8/5.5/5.5/3.8, a 6-point bridge 2.5/4.5/4.5/4.5/4.5/2.5, etc. Obviously, longer bridges or those that require steeper profiles, require more trial & error.

Cheers, Holger
 

arno

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Hi Holger,

Thanks for the information. I'm trying to create them from GIS data directly. I'll see if adding end points at -20 helps. Problem is that some of my bridges are 15 meter high and that seems to make the problem stronger.

All default bridges seem to use -3 meter for the end points, but they are not higher than 3.5 meter in height.
 
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Holger also previously shared his insights on related issues, and cited an excellent tutorial by Luis Feliz-Tirado ...here: :pushpin:

http://www.fsdeveloper.com/forum/threads/sbuilderx-bridge-question.116705/


That tutorial shows a "worked example" of XML code to generate an extrusion bridge.


For example KML code, see the attachment "fsxkml_samples.zip" in this post by Matthew Story, author of FSX_KML: :idea:

http://www.fsdeveloper.com/forum/threads/fsx-kml-tutorial-samples.5516/


Interestingly, Matthew_S also sets his extrusion bridge ends at -20M. :scratchch


Hope this additional info helps ! :)

GaryGB
 
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arno

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Hi Holger,

Thanks for the tip. I just put the last vertices a bit deeper (at -20 meters) now and that seems to have solved the issue. Still weird how it works, but I'm happy with the result.
 

arno

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Hi all,

I did some more investigation into the bridges and hit more issues. For example that the bridge doesn't get the altitude you specify in the xml.

In the end I found out that the bridge is always raised with the average height of all vertices of the bridge. So that also explains the floating.

After I compensated for that everything works perfect.
 
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