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Thread: Easements & Superelveation

  1. #1
    Join Date
    Jul 2011
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    Illinois
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    Default Easements & Superelveation

    Ok - based on the number of questions and frustrations I see and general lack of documentation, I've put together a little tutorial of how to use easements. I don't really think of myself as an expert, but I've been using easements rather extensively over the past few months in preparation for superelevation.

    Let's get started:
    Step1.jpg
    Above is the curve we will be making, this is a branchline that will be in my route, it is a complex curve having multiple radii present.

    Step2.jpg
    Here you can see the beginning of the curve. Easements have been turned on, the mouse is clicked to begin the curve.
    Arrow 1: grey line previews the path of the curve if it continues at the current radius (arrow 4)
    Arrow 2: purple lines preview path of easemented curve in ever shrinking radius (both to left and right)
    Arrow 3: yellow line previews path of straight track with no curves
    Arrow 4: points to current radius based on shown track length. (Mouse is at bright purple cross line which is 10.6M from 3D yellow marker
    To make this curve the radius must be locked in at approx 2563M. Zooming closer helps with precision for measurements.

    Step3.jpg

    Here the curve radius has been locked in at approx 2563M. The length of this section of the curve is will be 445M.
    Arrow 1: purple cross line indicates tangent point where curve will return to straight track.
    Arrow 2: purple line previews path of curve for smaller radius
    Arrow 3: grey line previews path of curve at current radius
    Arrow 4: white line (cross line) shows current position of mouse
    Arrow 5: shows information line displaying current locked radius and length of track section.

    As the curve radius is locked in (and right hand) there is no option for straight track (or left hand turn) without a transition easement to widen the radius. Favoring the mouse towards the right while advancing will highlight the purple preview and shrink the radius, favoring to the left will highlight the grey, turning it white and maintaining the radius. The very short purple section by Arrow 1 shows the radius widening towards straight, the mouse must be kept in this region to return to straight track.

    Step4.jpg

    The 445M section has been set, now the curve radius will need to change.

    Arrow 1: purple cross line indicates tangent point to return to straight track
    Arrow 2: grey line previews path of curve at current radius
    Arrow 3: purple line previews path of curve at smaller radius

    The curve radius must be reduced to approx 507M to stay in the trackbed shown on the decal

    Step5.jpg

    The end of the curve is in sight as is previously laid straight track. Ending an easemented curve is something of an art (at least for me) and involves a lot of trial and error. (Part 2 of this tutorial will cover the end of the curve)
    Arrow 1: white cross bar shows current location of mouse at locked radius (507M) and 155M from last section
    Arrow 2: grey line previews path of curve at current radius.
    Arrow 3: purple cross line shows point at which curve will return to straight track from current position of mouse
    Arrow 4: purple cross line shows point at which curve will return to straight track from beginning of current track section
    Arrow 5: purple line previews path of curve of shrinking radius from beginning of current track section
    Arrow 6: purple line previews path of curve of shrinking radius from current position of mouse

    Looking at arrows 1 & 2 it is evident that if the curve continues at its current radius it will never meet the straight track. The decal, visible below the path lines indicates that the curve widens approximately at Arrow 1. The curve section needs to be locked in at this point (155M)

    Part 2 to follow

    -barnez

  2. #2
    Join Date
    Jul 2011
    Location
    Illinois
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    Default

    Part 2:
    Step6.jpg
    The curve radius is widening to meet the straight track
    Arrow 1: purple cross line indicates tangent point where straight track may resume
    Arrow 2: current radius has been expanded to approx 1155M
    Arrow 3: grey line previews path of curve at current radius of 1155M
    Arrow 4: purple line preview path of curve at shrinking radius from current mouse position
    Arrow 5: purple cross line indicates current position of mouse
    Arrow 6: purple line previews path of shrinking curve from beginning of section with starting radius of 507M
    Arrow 7: grey line preview path of curve from beginning of section and maintaining original radius of 507M

    There is a lot going on in the above screen. The curve radius needs to widen so mouse position is favored to the left and radious expands accordingly. Confusion can set in from all the previews the key is to remember that they are showing the path of the curve from the start of the section and from where the mouse currently is. If the screen was taken with the mouse in a different postion, arrows 1, 3, 4 & 5 would all be in different places.

    Step7.jpg

    The curve is finished and straight track is now being laid to meet the track down the line
    Arrow 1: current radius is displayed 1.$ indicates infinite radius in easement mode (translation: straight track)
    Arrow 2: yellow line previews path of straight track
    Arrow 3: purple line (left and right - unlabeled) preview path of shrinking radius from current position of mouse
    Arrow 4: grey line previews path of curve at preview radius (1155M)
    Arrow 5: purple line previews path of curve with shrinking radius beginning from previous radius of 1155M

    The additional paths to the right are because the curve was to the right. Easements are set to return if needed to a right hand curve. A left hand curve can be begun at this time and would follow the path shown by arrow 3.

    The curve is finished, easements can be turned off. However, even after doing so tracklaying will act as if easements are still active. My solution to this is to run a 10M section of straight track. After that, tracklaying returns to normal mode and I will lay track forward until the next curve.

    This scenario however shows previously laid track to connect to, so how did I do?

    overlap.jpg

    Not too good I guess, the tracks are obviously offset by quite a bit (.45M to be exact). This is where easements can provide a tremendous amount of frustration - connecting 2 sections of track with easemented curves is not a simple process. I will show how it's done (at least, how I get it done) at the end of this tutorial.

    The next section will illustrate superelevation on the curve just made.

    Here are the full measurements (steps) of the curve just created (for those playing along on our at-home game):
    1: ease curve to 2563M radius (length of this section is dictated by easement algorithm and is constant)
    2: run section of 2563M radius curve to 445M long
    3: ease radius to 507M
    4: run section of 507M radius curve to 155M long
    5: widen radius to 1155M
    6: run section of 1155M radius curve to 85M
    7: straighten track, curve is complete

    - barnez

  3. #3
    Join Date
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    Location
    Illinois
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    So, what about superelevation? That's the easy part ... if everything was prepared properly with easemented curves.
    Why didn't I check the SE box when laying the track originally? I have found that SE won't display when done this way. I don't know if this is a bug or a design "feature" but SE is simple enough to implement without it.

    Obviously for SE to work it must be defined in the trackrule, I'm not covering how to do that here (there are other threads that discuss adding the needed data.

    For anyone interested, the trackrule I'm using here is custom but has identical SE properties to the HSC route.

    SE1.jpg

    This screen is towards the start of the curve, we are ready to add SE. Select track is active, properties are displayed and I've selected a run of track
    Arrow 1: shows the SE box unchecked, currently this is a normal curve with easements
    Arrow 2: points to a weld point (the reason I chose this section of the curve) this weld is key to making everything look right
    Arrow 3: points to the track behind the weld and also behind the selected track

    The 5M or so selection of track will apply SE to the entire ribbon between welds there is no need with SE to select the entire ribbon of track unlike when changing speed limits or line type. The section of track by arrow 3 is part of the curve (it is the easement leading to the 2563M radius section) but it will not be affected by SE because of the way I have selected the track

    SE2.jpg

    Arrow 1: points to the SE box, which is now checked
    Arrow 2: points to a visible seam that has appeared at the weld
    Arrow 3: points to the weld again (emphasis)

    Welds are both friend and enemy to SE. Welds stop SE - this is both good and bad. Good because it allows you to isolate sections of track like yards, where SE is not needed, or junctions, where SE appears to not be supported. The solution to remove the gap at arrow 2 with easements properly applied is to select a run of track on the other side of the weld. SE will not be active, the box can be checked and all is well. (Of course, knowing that SE will stop at the weld, obviously you can select the run so that both sides of the weld are selected and avoid the seam)


    SE3.jpg

    No arrows here, just a perfect run of easemented curve. Both sides of the weld have been selected and SE is active though the entire curve. The SE is subtle here because RSC has tied SE to curve radius rather than linespeed and the radius here is quite wide (for those used to US RR measures the curve is .68 degrees or roughly 41')

    For anyone playing the "at-home-game" with this little tutorial, you can fly down the curve and observe that SE is both visible and seamless.

    Next will come the tricky parts, a section covering converting non-easemented curves to SE, and I'll finish connecting the curve in the tutorial to the pre-existing track at the overlap section above.

    -barnez

  4. #4
    Join Date
    Jun 2008
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    Godinjak (Croatia)
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    Default

    Quote Originally Posted by barnez View Post

    This scenario however shows previously laid track to connect to, so how did I do?

    overlap.jpg

    Not too good I guess, the tracks are obviously offset by quite a bit (.45M to be exact). This is where easements can provide a tremendous amount of frustration - connecting 2 sections of track with easemented curves is not a simple process. I will show how it's done (at least, how I get it done) at the end of this tutorial...
    I layed 40km of tracks with many curves. I used easement tool so I could get superelevation. But I got a problem like on quote. Looks like impossible mission. After hours of trying I gave up. I would like to see a continuation of tutorials because I think it helps me a lot. Or will I have to make the second half route all over again?

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