Gradient problem??

[autodctr]

Saw this the other day while running a new route: at one point it said that I was going up a 3.9% slope! I wondered how this could possibly be since I choose the track slope and then build (lay) the track. Since the track was laid at approx 1.3 slope, this shouldn't have been. Exiting driving and then going and check that area, all was good: gradients ranged from 1.1 to 1.4. Today, while watching a different area of track, it claimed a gradient of 4.3%! I immediately exited driving and checked the slope.....none of the affected area was over 1.3%

Anyone have an explanation or has anyone ran into the same problem?

 

[RPearson]

...
Anyone have an explanation or has anyone ran into the same problem?

The slope that Surveyor reports is the difference in height between the current and next spline point divided by the track length between the 2 points. The Trainz track spline is a 3D cubic Bezier spline and bends between spline points - in both the horizontal and vertical planes. We are used to seeing the big curves in the horizontal plane and often use these nice looking free flowing curves in the track layout. But we don't expect see the small curves in the vertical plane or the effect they have on the track grade. The slope values you see in driver are the actual slope values of the spline (measured in the vertical plane) at the location of the loco. In CAB mode the grade resistance acting on any railcar is based on the actual slope of the track spline at the location of the railcar. Not the one calculated in Surveyor.

If keeping actual slopes close to the ones you input in Surveyor is important to you, you can do what real railroads do and introduce vertical transition curves - to transition between the sections of different constant grade. You'll have to use the straighten track tool to force Surveyor to make the track spline a straight line between end points both at the ends of the vertical transition curve and on horizontal curves. Something many route builders typically don't do. In some cases where a change in grade occurs on a horizontal curve this is not possible to do currently in Trainz (in a realistic fashion) without resorting to some custom fixed track sections. Fixed track sections could have been a useful addition to Surveyor if there was some way to set and fix their position and grades like normal spline points. Always moving when the ground is adjusted doesn't make sense for accurate track work. I find them awkward for normal use.

I've included vertical transitions and made extensive use of the straighten track tool on a fairly large route I've been working on for years and probably will never finish. I personally like the results but it's not easy and most of the track is not layed by hand. All the grades follow the original routes track profile including the vertical transition curves shown on those drawings. I made my own cad drawings of the route and exported the vector data. Most of us avoid this level of complication for building routes in Trainz.

Look at the sketch I made some years back trying to explain how the Trainz track spline compares to actual track layout and construction when viewed in the vertical plane:

Bob Pearson

PS The horizontal and vertical scales are not the same in the above sketch so the spline curvature is easier to see. There's also one dimension typo that crept in but doesn't affect the overall sketch.

 

[autodctr]

Thank you for the in-depth reply. I actually understand most of what you said! I just don't understand why I have never seen this problem before......I have made at least 10 layouts and never ran into this before. However, all of the other layouts were in 2017 and maybe that is why? Dunno. Just glad that you made some sense of it and now I can relax and not worry about the 6.1% grade that I found earlier today!

 

[rhban]

What I mainly notice is that if I lay a straightish section of track immediately following a downslope, it will sag in the middle. Shows up shockingly if I have inadvertently put water under that piece of land.