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Thread: Dem Grades & Accuracy

  1. #31
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    Im in the process of building a 200Km section of the NSW Northern railway (now closed) using 5 meter resolution DEM. The difference between this and previous DEM’s Ive used based on the NASA STRM files is amazing. The area I’m modeling runs basically north along some of the highest areas of the Great Dividing Range and has the highest station on NSW at Ben Lomond (1363m altitude) and steep grades of 1:40. The 5m DEM of this area is detailed enough to show cuttings and embankments where the track runs. The general look of the scenery, mountains, valleys, rivers etc is much more realistic than Ive seen before with the STRM based routes. Ive used TransDEM to lay in the track and build UTM tiles which help lay in the final scenery in enough detail to show every road, house, tree and fence line etc. Then in Surveyor it’s a matter of fine tuning the grades and alignments which Ive found is much easier with the 5M DEM based ground. In some cases the track is very close to the documented grades for the area, so the ground files are very accurate to reality. Also using the 5 meter grid in Surveyor helps so that when smoothing track you don’t get such a wide area affected.

    So my message is, try to get hold of the most highly detailed DEM file you can.
    PG
    Win10-64bit, Intel I7, 32GB RAM, TANE on SSD, GTX1050Ti.

  2. #32
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    Yeah unfortunately the DEM I have is one down from it and even Buffalo, NY doesn't have that coverage yet. I was fortunate enough to have a USGS image of my area across the border (but it was also missing a section from it's map in some parts but not all of Canada amazingly). So for the missing parts I believe I had 15m data from Canada and the US data is 1/3 arc. Fortunately other than the escarpment there is not that many grades and is relatively flat once above and below the escarpment.

    Now you brought up an interesting point I didn't think of as I haven't tried it since adapting the 5m grid to the track only in my last DEM build. Perhaps the smoothing may not be as bad so I might give it a try or at least try and carve out a path and see how things look. I never thought of that to be honest.

    I decided to only use the 5m grids on the boards with the route as I have a 13 baseboard width across the region for long views where applicable. Trying to get 5m on everything was killing my load times But I'll give it a try tonight. Glad you mentioned that!

    Thanks

    Sean

  3. #33
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    Sean, that narrow spline thing was mine. I use both at the same time - track on one layer, and spline on a working layer. I lay the spline over the track, do the smoothing, then delete and do little touchups. Good luck with it!
    Ron

  4. #34
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    One thing that shows up that is very easily fixed is culverts and creeks. Fortunately I have a good track map that shows where they are (because they aren't always easily visible). But a good clue is when you track dips sharply and comes back up. Just follow the track in Surveyor up to the point the dip starts and ends and add spline points. Level out the area to match both sides then replace the track.

    The video I took recently of local grade crossings and zooming is a huge benefit as well, because it shows the grade when you zoom in and can see miles in front of you at an exaggerated profile.

    The smooth features is good but unfortunately if your to do that with ditches it's going to make an average. I actually tried that technique first and didn't like the results. Of course when you don't have the visuals or actual data some times that may be the best or only option.

    Thanks

    Sean

  5. #35
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    Quote Originally Posted by Seane2c View Post
    Yeah I remember seeing the narrow spline post. It does sound like it's going to be too much hassle though. I'm already trying to plot in the spline points with the actual altitude of places like crossings that I can easily measure or estimate within reason.
    ...

    Thanks

    Sean
    I try to grade the whole route fixing the track spline height and then terraform the ground to match the track. I use survey maps or track charts of the route that have grade data. Or engineer it myself if little or no info is available. For the EBT RR I model I work to the survey maps produced in 1917. These give elevation data and grade and indicate distance along the track as station distance. There's also an indication of the ground profile below the track and the vertical transitions used at changes in grade. Data on all curves and locations of all junction, bridges, trestles, tunnels and crossings are also indicated.

    The 10m DEM data I'm using for the current version has most of the man made cuts and fills and also natural stream and river beds. In previous versions I had a mix of 10 and 30m DEM data and of course the definition wasn't as good but still usable. I decided to hold to the track line I laid out from the survey data and terraform the ground to suit. I use track with embankment/fill below it so I try to avoid the smooth spline tool and never use it where the fill is visible. Where the track is "submerged" in wide cuts and needs to be uncovered it is sometimes useful. For narrow cuts not aligned with the baseboard grid I just avoid it. When I do use it I mostly end up terraforming to reduce the width of the affected areas.

    From my experience using a "narrow or wide" spline to change the width of ground the smooth tool affects doesn't seem to work. The width affected is ~40m regardless. But using 5m vs 10m baseboards does have an affect reducing it down to ~30m wide. I have splines I use for invisible track that are only 0.1m in width. I also have a 100m wide track spline I use as a track tool in mountainous areas to help engineer track grades where I have to do the design myself. Fixing grade/elevations of the tool shows the intersection of the spline and the terrain within 50m each side of the centerline. It helps to see if reasonable cuts and fills are possible or I need to move the track a bit while keeping the grade set into the tool. The smooth tool has the same affect on both these splines as seen in the pic below. As noted the 10m baseboard in the foreground shows ~40m width in the total width affected while the 5m baseboard in the back shows ~30m total width affected.



    Bob Pearson
    Last edited by RPearson; October 16th, 2020 at 02:42 AM.
    TRAINZ-UTC-TRS04-TRS06-TC1&2-TC3-TS09-TS10-TS12-TANE(TEG)-TMR17-TS19
    Member since 6-14-2002

  6. #36
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    Actually that is very useful. I came to that same conclusion last night. I'm going to have to figure out how to use embankment fill. Is that an option in surveyor or the actual track you use? For now I did it manually and filled in a culvert last night with no issues. I was planning to paint in ballast around it but for now I'm not at that stage as I have full UTM's in place while I put everything down.

    Thanks

    Sean

  7. #37
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    Quote Originally Posted by Seane2c View Post
    Actually that is very useful. I came to that same conclusion last night. I'm going to have to figure out how to use embankment fill. Is that an option in surveyor or the actual track you use? For now I did it manually and filled in a culvert last night with no issues. I was planning to paint in ballast around it but for now I'm not at that stage as I have full UTM's in place while I put everything down.

    Thanks

    Sean
    Jointed Rail has track that has a deep ballast that will fill in underneath so the track isn't floating above the surface. User jim_spb made some embankment splines of various widths and textures. They're on the DLS as j_embankment. I recommend downloading them all. The textures are easily changed and you and replace his with those of your own choice. For other embankments, I recommend looking at those that begin with FMA there are various under-track embankments of various widths that may work for you.

    Other choices, of course, include various retaining walls. This is where FMA comes in and so samplaire and others.

    Remember, as much as we try to be realistic with this we can only do just so much because we are still stuck with a 5m or 10m grid. Maybe in the future when our computers can handle 8 x the resolution, or a 2.5m grid we can do stuff at a higher detail, but at this current point in time and technology even today some computers barely handle 5m terrain even in small amounts.
    John
    Trainz User Since: 12-2003
    Trainz User ID: 124863
    T:ANE Build: 94829
    TRS2019/Trainz-PLUS: 106618

  8. #38
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    Embankments can either be built into the track spline which makes it easier to work with or you can find separate embankment/fill splines that you run under the track spline and you can usually find them under scenery splines tab. I think it complicates grading a bit but makes it easier to work with 2 splines in close proximity.

    I prefer them built into the track and I have one that goes with the track splines I use for the ng track on the route. But most of that is single track territory. Separate splines allow for more variety in shape and textures and probably make sense when working with several parallel track splines.

    The 4 track PRR main thru the northern part of my route is wide enough where the smooth tool actually provides about the right width. The cuts and fills associated with it also show up clearly in the 10m DEMs I'm using but typically need some cleaning up. Zapping a whole section of track with the smooth tool to adjust the ground height here is tempting.

    Bob Pearson
    TRAINZ-UTC-TRS04-TRS06-TC1&2-TC3-TS09-TS10-TS12-TANE(TEG)-TMR17-TS19
    Member since 6-14-2002

  9. #39
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    I'll have take a look and find something appropriate. Most of my route is single track, and double track.

    Thanks

    Sean

  10. #40
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    So today I went back to do some walking and visual surveying. Of course the old handheld GPS I have at time showed me climbing the grade but as coverage changes it can changer very quickly (not sure how much clouds can change this as I had 30% cloud cover today approximately). But anything that is not detailed to 1M is garbage and those GPS I believe are accurate to about 30M.

    I've actually been looking at some altimeters and they can get quite pricey. Again I'm not sure if I want to go that much into this hobby but when I know something is not right I want to solve it, just in my nature.

    So if I haven't already this is the DEM I'm using and it's on a 5M grid on route baseboards only. The DEM was derived from USGS 1/3arc which I'm told could be anywhere from about 7 to 10m DEM matrix. The double track main where I'm surveying right now west of Grimsby, ON is about 10M wide on WNW to ESE straight line.

    I do not have grade charts for CN (and wish I knew how to get them). I was fortunate to get plenty of manuals of a retired engineer with CN. I also have signal charts which show grade crossing mileage, creeks, culverts, even bridge lengths, but not grades. The DEM traces some smaller areas such as 50 mile creek well (this was my target today). This bridge at MP31.4 of the CN Grimsby Sub is 83 feet in length according to the chart.

    Normally I have found that when it comes to overpasses creeks be it the road to rail, rail to creek, or rail to road the DEM will always default to the lowest position. Embankments though likely not natural and built up on a route that has been in place for a very very long time just doesn't show up. It actually shows flat. Now granted this is not a wide embankment (about 10m wide). I was able to locate the lower apex of the grade at Kelson Ave MP30.90 when I walked half a mile west. You could tell there was a grade going up and indeed we were getting higher.

    By the time I got to the bridge I climbed down to what was a private road that followed the creek. I estimate that the height of the bridge was about 15 feet though I'm going to look at the video and take some images again with about a 12 foot clearance. At the very least the trek got me a side shot and I found some piers I didn't know existed and wasn't visible in Google Earth (so all is not lost).

    I believe I can get a good idea of the lower apex within a meter or two since it's not that much higher than the road height on approaches. However it gets more difficult to guess without proper measuring devices or charts what the actual apex top of the grade is that I can plainly see in both regular and zoomed out optics.

    Is there anyone here who can recommend a good altimeter that works at 1m accuracy? I know there are plenty out there that say it. Complaints of having to adjust all the time etc. because the weather changes. I think people there perhaps just have too high of expectations. They are also trekkers who likely climb higher altitudes and take less altimeter readings to adjust properly in changing conditions. For me I'm likely only traveling no more than a mile at a time by foot so the weather shouldn't change that much and I can take another altimeter reading to confirm this.

    I guess I'm looking for some experience on this matter in the field so I can make sense of what my eyes are seeing. Thanks for all the help guys, please keep it coming. Hopefully I'm helping others in other topics as well.

    Thanks

    Sean

  11. #41
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    I always wanted a Trainz route of the Niagara area. There were some made but they aren't accurate. There is a huge blank DEM on the DLS of the Niagara area but the Ontario, Canada side is blank, no TIGER lines. I too struggle with gradients especially on those old HOG blank routes made by fishlipsatwork, smooz, etc. Sometimes there's ugly gaps like V or raised ridges and raised points like /\ in the terrain. The uneven terrain where the light blue track lines are really frustrates me. Especially with mountainous and hilly terrain. Without track charts of a particular line I have to guess the gradients. Any tips on working with HOG maps to get better results?

  12. #42
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    Might want to check out my youtube links, you might enjoy it. The only reason why I didn't download a Niagara route is I'm too cheap to buy a ticket Yet I'm crazy enough to want to get an altimeter to get my route right

    I do almost daily live streams and I'll be doing one shortly on the Jordan Viaduct and a very suitable fill in (not perfect). As I've been told compromise is key here. One of these days either my son or I will learn how to do our own assets. Until then I so appreciate the sharing of so many talented individuals.

    Thanks

    Sean

  13. #43
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    I have to remember that this is all about compromise if you want to have fun and not lose your mind When I was streaming tonight I recalled the days when if I just had some plywood and an operation with a model railroad I was happy. Anyways the build of the scene should be up on my channel later. The bridge was only 30 meters short but fit right in and has done more than an adequate job.

    I've posted some screenshots of the crossing as well. Had to dredge the harbour a little bit from the DEM as I needed to lower quite a bit, but it fit nicely in the end.

    Once I'm finished the track alignments, grade crossings, and signals I'll add in the trees and rest of the scenery to complete this scene.

    The way I see it right now the DEM accuracy is as good as the data. TransDem has been a great purchase for me allowing me to carve out realistic scenes quickly and concentrate on the route and bridges like this.

    Thanks

    Sean

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