Low Resolution DEM - potential issues

[scottb613]

Hi Jerry,

Sounds like you have it sorted - have fun...
😉

Regards,
Scott

[landnrailroader]

Friends, in my latest attempt to get data for a route, in this case the former Tennessee Central from Nashville to Harriman, TN, I downloaded 6 geotiff, 1/3 arc-sec files from USGS and not a single one would process & then save using VTBuilder. I downloaded what I thought might be a new version, but the current version I have is from 2013 and that is also the current download version. So I looked at QGIS - so folks, could one of you write up an instruction as to what is needed - none of it makes any sense. I got the QGIS Desktop, 3.40.14 which when opened says it is the Long Term Release, Bratislava. Advise if this is correct or if I need something else, and then how do you read in a .tif file and then output a new .tif file. Prior to this, I was able to get files that worked so as to add a little more terrain to the Chattanooga line about 8 weeks ago and they were okay.

Jerry Sullivan

[rt35ge]

Don't know if this site will help or not Jerry. It's what I use for DEM data. Mind you I have Train Simulator Classic so I don't know if it''ll work for you..... I gave up on USGS ages ago cause they kept moving the goal posts. https://dwtkns.com/srtm30m/

[PerryPlatypus]

Friends, in my latest attempt to get data for a route, in this case the former Tennessee Central from Nashville to Harriman, TN, I downloaded 6 geotiff, 1/3 arc-sec files from USGS and not a single one would process & then save using VTBuilder. I downloaded what I thought might be a new version, but the current version I have is from 2013 and that is also the current download version. So I looked at QGIS - so folks, could one of you write up an instruction as to what is needed - none of it makes any sense. I got the QGIS Desktop, 3.40.14 which when opened says it is the Long Term Release, Bratislava. Advise if this is correct or if I need something else, and then how do you read in a .tif file and then output a new .tif file. Prior to this, I was able to get files that worked so as to add a little more terrain to the Chattanooga line about 8 weeks ago and they were okay.

Jerry Sullivan

1. Upper left corner, click Project -> New Project
2. In the "Browser" at left, navigate to your TIF file. (Or right click on "Favorites" and "add a directory" and select the folder where you are placing GeoTIFF files)
3. Right-click on the GeoTIFF file, select "Add layer to project".
4. Down below under "Layers", right click on the same file, choose "Export", choose "Save As"
5. Most likely all of the important parameters will auto-populate, and all you will have to do is click the button with three dots to the right of the "File name" box, and choose location and filename for the export file.
(If the "CRS" field does not auto-populate, a safe bet is to pretty much always go with "EPSG:4326 - WGS 84" for the export coordinate system)

If you ever need to convert between two coordinate systems (USGS one-meter DEMs usually come in with a different native coordinate system), you can use the top menu bar in QGIS and select Raster -> Projections -> Warp (Reproject). For source CRS you would choose whichever one is the "Project" one, and for Target CRS you would choose EPSG:4326 - WGS 84.

If all of the GeoTIFFs you are working with have the same source CRS, you do not need to start a new project for each file. But if they do (or you are unsure), it is safer to start a New Project for each file so QGIS doesn't get confused thinking you are blending multiple coordinate systems.

[landnrailroader]

Sean,

Thanks that worked like a charm. I did get those "tag" errors when I went to use the files but as others have said, those meant nothing and the converted files worked fine. This route, if I ever do it, will be the Tennessee Central east of Nashville. Originally it was a shortline built around 1900 to provide an alternative to the L&N or NC&StL for traffic in/out of Nashville and eventually it was extended northwest to Hopkinsville, KY and east to Harriman, TN. At Hopkinsville it connected with the ICRR and at Harriman, (and Emory Gap) with the Southern. For several years it was jointly operated by the IC and SR but then reverted to independent status by the time I was born (1939) and fascinated by a train passing over a trestle about 4 blocks from our home, so much so that my mother demanded that my father find a house further away from a track, but the railfan insect had bit me hard in the butt and it is a terminal bite. In 1969 with bankruptcy in view, again, the IC took over the Hopkinsville to Nashville line, Southern got Crossville to Emory Gap, and L&N got the rest. Now the Nashville & NorthEastern owns it and operates northwest to Ashland City, TN with the line abandoned beyond there. The line is abandoned between Monterrey & Crab Orchard with Lhoit having a line that runs from he quarry at Crab Orchard to Emory Gap, although the interchange with NS is now at Rockwood. The N &NE operates Nashville to Cookeville and the track is still in place to Monterrey. The Music City Star commuter operation runs between Lebanon & Nashville and that portion now has signals & TCS in place.

Again, thanks, and hopefully others with the same issue will see your explanation which was easy to follow. I found it a bit less confusing to create a new project for each file but that was just me and others make prefer to not take that route.

Jerry

[landnrailroader]

Thanks RT35GE but I tried the other sims some time ago and stuck with MSTS/ORTS simply because the feel of running the train was not right. Although none of the sims bounce you around like a real engine, as far as I know, I found the visuals and all better with MSTS. During wildcat strikes 50 years ago on the SR, when I worked there, I got to run a few trains and I based my thinking on those trips.

Jerry

[eric]

Glad you got it worked out.

Franklin Limestone in Crab Orchard is alive and well. We were just out at Ozone Falls a month ago, and there's a beautiful old-school wood timber trestle visible from US-70....

https://maps.app.goo.gl/gHjZL9rMj4aMNpMT7

[PerryPlatypus]

Sean,

Thanks that worked like a charm. I did get those "tag" errors when I went to use the files but as others have said, those meant nothing and the converted files worked fine. This route, if I ever do it, will be the Tennessee Central east of Nashville. Originally it was a shortline built around 1900 to provide an alternative to the L&N or NC&StL for traffic in/out of Nashville and eventually it was extended northwest to Hopkinsville, KY and east to Harriman, TN. At Hopkinsville it connected with the ICRR and at Harriman, (and Emory Gap) with the Southern. For several years it was jointly operated by the IC and SR but then reverted to independent status by the time I was born (1939) and fascinated by a train passing over a trestle about 4 blocks from our home, so much so that my mother demanded that my father find a house further away from a track, but the railfan insect had bit me hard in the butt and it is a terminal bite. In 1969 with bankruptcy in view, again, the IC took over the Hopkinsville to Nashville line, Southern got Crossville to Emory Gap, and L&N got the rest. Now the Nashville & NorthEastern owns it and operates northwest to Ashland City, TN with the line abandoned beyond there. The line is abandoned between Monterrey & Crab Orchard with Lhoit having a line that runs from he quarry at Crab Orchard to Emory Gap, although the interchange with NS is now at Rockwood. The N &NE operates Nashville to Cookeville and the track is still in place to Monterrey. The Music City Star commuter operation runs between Lebanon & Nashville and that portion now has signals & TCS in place.

Again, thanks, and hopefully others with the same issue will see your explanation which was easy to follow. I found it a bit less confusing to create a new project for each file but that was just me and others make prefer to not take that route.

Jerry

Glad to hear it worked out Jerry! The main benefit to doing things as a single "project" is if you are converting a very large number of files at once. QGIS has a powerful "batch" function (which I did not attempt to describe at all above) where it can run a conversion or re-projection on a ton of files all at once and export them into numerous files with unique sequential filenames. This is especially helpful when using super high-resolution 1/9th arc or 1-meter DEMs which cover rather small geographic areas, as it can be very laborious converting dozens and dozens of those for a route.

[landnrailroader]

Sean,

I understand, however I seldom need more than 10-12 files max for routes and this one may be my last - if I get around to populating it. Yesterday, I copied the desired world files from the Nashville Terminal (which is used in 3 or possibly 4 of my routes, and from the CNOTP3 route. After doing that, I edit the world files to remove any dynamics and all of the under track transfers using Context Editor. It is easy then to add back in the dynamics where necessary by just noting the parameters from the host route. At that point I guess I could run the database rebuild but I prefere to manually select each piece of track & road so that in the process I can find other things that need to be deleted.

In 1956 I rode the engine of the weekend excursion train that TC ran in those days from Nashville to Harriman & back. Took about 14 hours to do it - this being during the days of the 16 hour law. Then around 1970 or so, I rode it again on my track geometry car over the part that SR got in 1969 - kinda nervous about all those wooden trestles but we did okay. Jere Baxter was a famous Nashville businessman of the early 20th century who spearheaded building this line. The main downtown technical highschool is named for him & other things.

Jerry Sullivan

[eric]

Those wooden trestles were built to last, as long as the vandals don't get to them

[landnrailroader]

Eric,

Built to last, well yes & maybe. The bridge man at the time kept a list of where he could "borrow" this and that from one trestle to repair another. By 1969, the old TC was bellly up and the tallest wooden trestles, some nearly 100 ft. were east of Crossville, i.e. the part that SR acquired. Later SR filed to abandon the segment but Franklin Minerals acquired the part from Crab Orchard to Rockwood, with most of the trestles (three are steel, similar to Milwaukee Road trestles in that there are no horizonal stiffening members). Then Lhoist, a European company acquired Franklin Minerals and as far as I know the railroad is still in use to deliver from the quarry to NS at Rockwood. Come next fall, Eric, take a nice drive over to Crossville and if you do take US-70 one way and then come back either that way or by I-40. Many of those trestles are visible from US-70 as is the only tunnel, through the gap west of, and above, Rockwood. A railfan friend, and fairly frequenter to this website lives in Rockwood. He also has a program of gospel music on the TV station at Oak Ridge and he is pastor of a rural Baptist church near Ozone. Ozone falls is a nice short walk from US-70 but BE CAREFUL, there have been fatalities when folks got to close to the edge on wet rocks. The falls are a state park and around 150' high.

Jerry Sullivan