Low Resolution DEM - potential issues

[landnrailroader]

As I believe I have mentioned, I have not been able to use 1/3 arc-sec. DEMs in DEMEX even if preprocessed by Virtual Terrain Builder (VTB) which is reqired to use 1 arc-sec DEMs before DEMEX can handle them. This leads to an interesting situation on the Kentucky Div. route I am laying track for. At coordinates -84.2754/37.3747 there is a very short tunnel through a small ridge that lies in a bend of Roundstone Creek. This tunnel is barely 150 feet in length with a bridge over the creek on both ends. However, with 1 arc-sec data, the ridge ends east of the tunnel and the route of the track (which is nearly level anyway) is across a flat area. Then further north there is Tunnel #14 which is much longer and through a well defined ridge. So beware, those of you that are creating routes, some elevation areas may not be true to what is really there. I will place a tunnel section where the tunnel is supposed to be and then someone can manually shape the rest of the ridge when the route is released.

I would hope that someone could come up with a version of DEMEX or something like that which would use the higher resolution data but it must be realized that it would be a somewhat futile effort. USGS tends to change the format of DEM data at will and for example, the higher resolution data worked fine until about 5 years ago and then there was a format change. A file processed by VTB is about 1K smaller than the raw file, so there is something causing an error?

Jerry

[Coonskin]

Hello Jerry!

Good to see you're still kickin' and involved in projects!

The DEM situation for me has been an issue for quite some time. I was unable to download usable DEM until you taught me how to download at the new website location, AND, you also taught me how to use VT Builder to make the necessary changes in format so the DEM could be used by DEMEX. I "thought" you had put that in tutorial form, and I also "thought" I had saved it.

Unfortunately, I can't find it anywhere on my hard drive.

Did you compile a step by step tutorial on how to currently download DEM in what needed format, then how to covert it using VT Builder? If so, did you post it and do you have a link, to it, or was it in zip form and you still have a copy you can share?

I'm looking at a project (modifying an existing modern era route), but frankly, given the HUGE differences between the target route in 1882 compared to modern times, I would probably be better off to start with fresh terrain!

Andre

[conductorchris]

Hmm, I was just wondering something about this. I wonder how hard it would be to add this kind of functionality to TSRE? I recall earlier discussions about this with Goku.

[landnrailroader]

Andre, I didn't create a tutuorial because the process is pretty easy. Go to this website: https://apps.nationalmap.gov/downloader Once there, you can use the map to go to the general area of where you want DEM files. So far, the only ones still usable are the 1 arc-sec version. You can select the option to define a rectangular pattern where you want to get files for and then in the type of data area over at the right side of the screen, select elevation and then uncheck everything except the low resolution data that you see. Once the files are downloaded and each is about 50M more or less in size (the better 1/3 arc-sec files were 500M or so, and thus contained a lot more data). Now get VTBuilder and install it. Run it and the instructions are a bit hazy but you select the type of data you wish to import, and then select the desired file. Once it comes up, a screen will appear that shows a picture in 2D of the expected terrain. Now under export, save the file as a geotiff file just using a different name than the first - I usually just tack on another character at the end of the name. If it saves without errors, you have a file that is digestable by DEMEX, but again, pee-poor resolution, but it is the best we have and much better than .hgt files.

[Coonskin]

landnrailroader

Thanks Jerry!

I have copied the above and saved to my VT Builder folder.

Yes, I have VT Builder installed from the last time we had this discussion.

I may give it a go on the Raton area and see what happens. Then again, I may not! (As an option I'm still seriously considering using Bob Wirth's Raton 3 route as the basis.)

Andre

[landnrailroader]

Andre,

I would probably use Bob Wirth's route if I knew he had used higher resolution data. Since we probably don't, my next choice would be to create the new empty route and run Demex on a small portion that also exists in Bob's route. Then compare the results and decide. I keep an old XP machine in my office, er playroom, but I don't dare connect it to the net, so I use thumb drives to transfer data. That usually works but it is SLOW. I've never been able to get MSTS to install on my newer -7 and now -11 machine, so I know of no way that I can use DEMEX on it. It is a 64 bit OS which may be the problem? All of the routes I am currently working on were set up and DEMEX was run on them by 2020 or earlier and then stored on CDs or DVDs. However some, like the Kentucky Division I am currently laying track on were done with the lower resolution material. Oddly, TSM runs fine on -11.

Jerry

[Coonskin]

landnrailroader

Boxes:

Yes, that's my set up too: Offline XP box for development, online Win7 (now ancient) for running the routes.

Terrain:

I had to address some tile misalignment just map west of Raton near Goat Hill. (Had some hills missing their eastern half, thus some 100'-200' sheer bluffs), but otherwise the terrain looks nice in Bob's route.

Bob's work vs starting over:

Plus, he's already got the line all the way to La Junta to the east and Las Vegas to the west. Should I do this 1882 backdate project, and should I ever get the urge to expand past Trinidad to the east and Dillon to the west, then in theory I already have the basic main in place to those points PROVIDED I can get the interactive objects removed without incident. (The route crashed on me and wouldn't load in AE after reaching La Junta with the removal of interactive objects. I had to revert to a back up. Go figure.)

Go/No Go:

I'll figure it out. 😀

Andre

[scottb613]

Hi Folks,

Hmm - I don't have issues with 1/3 arcsec or 10m DEM on Win10x64 using DEMEX.

I've used both VTBuilder and QGIS to process the raw files from USGS - for import into DEMEX. Both applications work - although I think VTBuilder throws a "tag error" that seems to have no impact.

• Our Terrain Mesh in ORTS is 8m resolution.
• HGT DEM is 30m resolution.
• GeoTIFF DEM I've seen down to 1m resolution - although I only use 10m resolution or 1/3 arcsec

This is definitely 10m - look at the sharp cliff lines.
51942810428_7600d19aab_o.png

Regards,
Scott

[scottb613]

Hi Folks,

Perhaps I'm not following correctly - the 1/3 arcsec or 10m is still available. I have it selected, and it shows the coverage.

Capture.jpg

Regards,
Scott

[landnrailroader]

Scott,

It is stilll available, that was not the issue. The issue is that I have been unable to get VTBuilder to process it and remove whatever the issue is that burps DEMEX. At the moment, I have created all the routes I expect to produce and generated terrain using the lower resolution data. I wish we had some products that would allow us to create routes outside of TSRE, create terrain with something like DEMEX, and use higher resolution data, 10M is sufficient, but I dream on--------.

Jerry

[scottb613]

Hi Jerry,

Ah - OK - when I get a minute - I'll try a fresh download of 10m DEM - process it - load it into DEMEX as a test to make sure it works. When done - I'll post it here so you can try loading it into DEMEX yourself.

Regards,
Scott

[scottb613]

Hi Jerry,

I'm on my backup PC at the moment - just downloaded and installed a fresh copy of VTBuilder - loaded fresh 10m DEM from USGS - exported with no errors.

My DEMEX is hosed - complaining about invalid license - I had it installed on this old box before - odd.

Let me fix my DEMEX issue.

Capture.jpg

Regards,
Scott

[scottb613]

Hi Jerry,

I installed a fresh copy of DEMEX from the version in the FL. DEMEX loaded my processed DEM without issue - all good.

To process in VTBuilder - I just loaded the DEM into VTBuilder and hit EXPORT - super simple.

While I didn't use it this time - I typically use the "Beta 02" of DEMEX - as John figured out a way to paint the screen much faster.

If you think you need me to upload my processed test file - I can do that to - just let me know.

10m DEM:
Capture.jpg

Regards,
Scott

[PerryPlatypus]

FWIW, years ago (probably close to a decade at this point) I started getting inconsistent results with VTBuilder exports. Sometimes Demex would accept them, other times it wouldn't. I started using QGIS instead, and I have *never* had any issues since. Every 1/3rd arc or 1/9th arc DEM that I have exported from QGIS, Demex happily creates terrain with. As simple as making a new "project" in QGIS, adding the downloaded GeoTIFF as a layer, and exporting again as a GeoTIFF.

(QGIS also has a whole lot of other capability, like taking 1-meter data that is natively in local coordinate systems (which causes Demex to place it in the wrong spot), and "warp" / reproject it to a universal coordinate system that is compatible with Demex / ORTS.)

[landnrailroader]

WHOOPEE,

Well gentlemen, I downloaded a 1/3 arc-sec item that covered Mt. Vernon, KY which is where I had added a few tiles a couple weeks back to the Kentucky Div. route. Then I massaged it with VTBuilder, no errors reported. Then I put it on a thumb drive and ported to my XP machine and ran DEMEX. No errors there either and when I opened the route in MSTS/RE it looked okay with better looking raw terrain in that area. One thing I noticed is that the publish date of this data was in 2024. I had trouble starting around 2020 and have only used the lesser data since, so my guess is that USGS may have corrected some of their own errors. I did not try using the original, pre-VTB process file. So for this route, I believe I will go ahead and download the 1/3 arc sec files for all of it and regen at least the regular mountain terrain. Distant is less critical about resolution.

So then I downloaded 7 more 1/3 arc-sec dem files and processed all of them with VTBuilder. Of the 7, only one had an issue, and when it produced an exception handler comment on saving the exported file, I just ignored it. Took the files to my ancient XP machine and every one of them loaded into DEMEX fine and all tiles in the Kentucky Div. route were updated. So I took it back to my Win-11 machine and backed up the original just in case, then deleted it from the working directory and loaded the new version in. My most serious check would be to see about that tunnel I mentioned earlier that was in a flat area when terrain was produced by 1 arc-sec data. Voila, nice ridge, tunnel is in it, and just to the east a few meters is a cut that was made when the 2nd track was added around 1915. Oddly, it was the track through the cut that has since been removed. I would have thought the tunnel would have gone first. So, evidently the USGS files from 2024 have corrected some things in earlier versions and at least for the moment things work okay. I downloaded the installer for QGIS but I'm not keen on learning a new program as long as old VTB does the trick, so I won't install it for now. I have 4 or 5 routes that still have the low res. terrain so as long as my XP machine soldiers on, I will update those with 1/3 arc-sec data. I also want to update my Kingsport and Blue Ridge Sub. routes because I am a bit at time, bringing those up to my current standard which means 99% of the dynamic track gets removed. I did those routes before we ever heard of X-tracks, let alone M-tracks.

Jerry