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Thread: How to fit a trestle to curve & grade----

  1. #1
    Join Date
    Nov 1999
    Location
    Jacksonville,, FL, USA.
    Posts
    3,943

    Default How to fit a trestle to curve & grade----

    Friends,

    In doing a route for a friend in Tennessee, I knew that the Tennessee Central had several timber trestles. I found that the limit on polygons for
    my system was around 4,000, so I resolved to break these trestles into 2 or more sections, of less than 3500 polys each as some of the trestles would have topped 9000 if not divided up. It does not matter what you use to create the trestle (I use TSM) or what you use to place them. (I use MSRE to
    place them and TSRE to align them to the track).

    Two factors are involved. Is it on a curve? and What is the gradient? The one I just fitted is on a 6 degree curve with 30 meters of tangent on
    the low end, and it is on a .412% grade. It is useful if you put a marker on the low end when you create the trestle and then delete the marker and regen. the object when you have finished placing and aligning it. I use M-tracks, so the track chart said 6 degrees & I used 6 degree pieces.

    6 degrees comes from surveying the curve. The original surveyor would have put his transit on the last tangent stake and back sighted along the tangent. Then he would have flipped the transit and rotated it 6 degrees in the direction of the curve and measured out 100 feet from the tangent stake placing the first curve stake. There are many ways to do this but suffice to know that at each point of the curve there is another 6 degrees of swing until tangent track is reached again. Okay, deck pieces for a wood trestle can be any length but the Milwaukee Rd. used 16 feet. Using a little Algebra here we use the formula: 6 X
    __ = __
    100 16
    or (6x16)/100 which yields .96, thus each 16 foot panel needs to turn .96 degrees more than the previous one (rounded).

    The change in level of each piece for .412% is calculated the same way. Since .412% means a rise of .412 feet in 100 feet, these increments are going to be very small.:
    (.412 x 16)/100 = .066 (rounded)

    I create a tiny block, .066 on each side, and use that to rotate my deck pieces to fit the grade. What I do is create the entire length of the trestle, only the deck pieces & the end berms. Then I place this deck piece, call it a template if you wish, and adjust it with TSRE to align properly. I may have to go back into TSM or whatever is used to create the trestle & make some adjustments. After I am satisfied, I go ahead and finish the trestle adding the under pinning knowing that the result will upset MSTS but maybe not ORTS. So then I break the finished trestle into 2 or more parts, generate them separately and then place them, adjusting the fit.

    The left image shows 3 completed trestles. All have timber in them, the near and far ones being totally timber. The middle one has a section of steel trestle which is over a ravine too deep for wood trestle parts. The right image is of just the deck for a trestle that can be seen by cars passing on old US-70 to the right. After it is completed, I will break it into at least 3, possibly 4 parts. The "S" curve trestle on the left is in 4 parts. On the right image, the blue object in the distance is a 5x5x5 cube used to mark the low end. I don't use the side bracing as that would just add more polys. One way to "fake" that would be to use a 2-sided transparent polygon and put "X" marks on it to simulate the side bracing, but, life is short-----.

    J. H. Sullivan, P.E. retired from CSX & SR
    docent: C&TS RR
    Attached Images Attached Images

  2. #2
    Join Date
    Nov 2007
    Location
    SW MO
    Posts
    545

    Default

    TSRE will do this.
    You use the Auto Placement tool.
    You will have to isolate the track where you want your bridge by selecting a track piece on either side of your workzone and removing it from the TDB by hitting Z.
    Select Z to turn it off, select Z to turn it on.
    Go ahead the click on the three dot menu button and you'll see more options.
    It's really pretty cool what you can do with this.

  3. #3
    Join Date
    Nov 1999
    Location
    Jacksonville,, FL, USA.
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    3,943

    Default

    All well and good if you use TSRE. I don't just because the learning curve is a bit steep and at 82 I'll stay with
    MSRE which is the method I use to roughly place the pieces. I do use TSRE to align them. For example 4 of the
    trestles I have done (one more to do) totaled over 9000 polys. I could have placed them with MSRE but then
    the next time I entered that world tile, the item would be rejected, so with 4 pieces I kept the count of each
    around 2200 or so. TSRE does allow very precise adjusting of alignment and that was a great help. If I am
    dealing with a shorter bridge on a tangent track, or road, then TSRE is invaluable to getting precise alignment
    to the track or road. Only problem I have is how in the [email protected]#$%^&* can you force the item to align only to the
    "Y" axis and not that plus the "X" or "Z".

  4. #4
    Join Date
    Nov 2007
    Location
    SW MO
    Posts
    545

    Default

    If you leave the Y and Z set at zero they should have no effect.
    If you are using Stick To Target that will mess with TSRE's placements.
    Are there any shapes you are using that I can fiddle with? I have most, if not all, of your stuff.

  5. #5

    Default

    To force your supports to use only the Y value, go into the W file after placing, and modify the QD by replacing the second and fourth values with zeros -- that will give you the rotation but not the incline (which I hope is how supports should be placed).

    If poly counts are an issue in the MSTS, create or borrow a placeholder piece that won't cause the RE to barf, and then replace that shapefile name in the W later for being able to use in ORTS. Again, it requires some W file editing, but I am guessing you're no stranger to that.

    This is one of the reasons I created WorldFileHacker... curved freeway bridges on an incline... WFH can be set up to pair those curved track/road sections with multiple companion objects -- in this case the deck and the support. The deck piece shares the axis point and the incline of the track or road, while the support is set to ignore the incline.

    You can do the same without WFH by placing the object manually using the MSTS RE, closing down, opening up the W file and replacing the Position and QDirection for the manually placed deck/support with the the Position and QDirection from the related track piece(s).


    My objects are built in Sketchup 8.0, and there's a script plug-in in the library you can use to create a curve that matches MSTS/ORTS curvature where you can also define how many straight segments to break the curve up into (similar to how curved track gets extruded). On a larger 5d curve, I might break up into 10 straight sections. On a smaller 5d, I might only have two straight segments.
    Last edited by eolesen; 06-06-2021 at 03:54 PM.

  6. #6
    Join Date
    Nov 1999
    Location
    Jacksonville,, FL, USA.
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    Default

    That is correct. When I create the pieces of the trestle, I build in the gradient so that when placed, the
    "supports", i.e. the "bents" are vertical and do not have a lean as would be the case if the deck were
    tilted when placed.

    Yep, no stranger to editing world files. In this case the route was originally done roughly by the lad
    that asked me to finish it, but he had world file object counts as high as 900 - he used individual trees.
    It was easier to edit the world file rather than manually delete the trees. He did not understand
    forest objects and needed THICK forests. To do that I use 3 forest objects at the same location
    at different angles and it works okay. The route is the former Southern, now NS route from
    Oakdale to Chattanooga, TN and it includes the former Tennessee Central from Emory Gap to
    Crab Orchard which is now owned by the company that owns the quarry at Crab Orchard. I have
    laid track on into Crossville that was abandoned in 1986, so I will put scenery blockers at the
    point of abandonment and if someone else wants to use my work as part of doing the old
    Tennessee Central (went on to Nashville, and another line from there to Hopkinsville, KY)
    they can copy part of my route into the new one - if they know how to edit world files,
    cackle, cackle----.

    J. H. Sullivan

  7. #7

    Default

    900 is a high count for MSTS and the MSTS-RE, but it won't bother ORTS or TSRE.

    Overlapping forest objects is indeed a lot easier to manage.

  8. #8
    Join Date
    Aug 2002
    Location
    Poteau, OK, USA.
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    4,695

    Default

    900 objects:

    Depends on the objects, I suppose. I build my structures as "cheaply" (polys/textures) as practical and try to be conservative with use, but even at that I have tiles that are 4 digit, some adjoining each other. That's not a problem on my old XP development machine, though I can see the load when in RE. However, regardless of what route I've run to date on my Win7 machine, the FPS stays pegged at 60 or upper 50s, and that with straight MSTS/Bin, not OR.

    Whether MSTS, OR, or whatever, I really do feel there is resource management involved. There ARE limits on each sim platform. Just some higher than others. Simply put: One can't expect to run 100+ car trains with high-poly/texture models, have 4-digit object placements of high-poly/texture object models, and huge ultra-detailed terrtex patches... and still expect to load the activities with loose consists, AI, etc, etc, and then wonder why the system is loaded down, or having sporadic crashes.

    Of course, the above is just my opinion and it's worth as much as it cost to read it.

  9. #9
    Join Date
    Nov 1999
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    Jacksonville,, FL, USA.
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    Default

    But your opinion is correct. I suppose you could max out the memory on your PC and have a large SSD to house the
    operating system & simulation but some of us are on limited incomes??

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