3m DEMS?

[rs2007]

So, I recently purchased TransDEM to finally get a start on my GTA route, I tested the program by creating a line between Toronto and Barrie. I was using a 70m DEM. What ended up happening was that there were a lot of hills in the Toronto area rather than being flat. I heard that there are places where you can get 3m DEMs. Is there such things as 3m DEMs because I cannot find them.

[schweitzerdude]

I can't answer your question directly but I have a possible reason for the problem. I use 30m DEMS (SRTM) and you might want to try them. But in my experience DEMS will be somewhat inaccurate in areas with tall buildings or lots of trees. Can you correlate your hill problem to buildings in downtown Toronto? I ran into this same issue when I used a 30m DEM that included Vancouver BC and found that bumpiness was most pronounced in the downtown area. I think we are stuck with this.

[JCitron]

I can't answer your question directly but I have a possible reason for the problem. I use 30m DEMS (SRTM) and you might want to try them. But in my experience DEMS will be somewhat inaccurate in areas with tall buildings or lots of trees. Can you correlate your hill problem to buildings in downtown Toronto? I ran into this same issue when I used a 30m DEM that included Vancouver BC and found that bumpiness was most pronounced in the downtown area. I think we are stuck with this.

I can confirm that's an issue. In my area we have hills and lots of them. They're only about 220 meters high and quite steep on one side being glacial drumlins with a smooth slope on the other. These hills are quite obvious, however, there are other anomalies that occur in the old factory district near the downtown. The mainline runs along side one of the hills up on an embankment with bridges over roadways below, and abutted against old shoe factories on the other side. Where the roads, factory buildings, embankment, and hill are in close proximity, everything got averaged together into a blob about 14 to 15 meters above the roadways below. Crossing over the river, and the mess got worse. The landscape ended up mushing out a railroad branch line completely into a bridge, and the downtown part of the city is at the wrong height since all the buildings, not very tall mind you, ended up mushing together completely.

As I got more and more into the project, I decided it wasn't worth the effort and gave up. It was too painful having to undo the mess that was created by the low resolution DEM. If I were to start the project again, I may go for the 1/9 arc-second resolution, which is much higher, and use a 5 meter grid.

[rs2007]

That may be the case but there were also hills on the track area as well, but considering the fact that most of the hills were in the Toronto area that does make sense.

Where did you get the 30m DEMs? I am trying to make my route as accurate as possible and that may be useful.

[PGibbons]

I would recommend trying to obtain the most detailed DEM available for your area of interest.
Ive used 2m & 5M DEM for my current route based in northern NSW where the terrain is very mountainous. The detail produced by TrandDEM creating TRAINZ 5M GRID is better than Ive seen before using SRTM data. Everything is much more detailed down to creek beds, road and track embankments and cuttings, etc, and the elevations are very accurate. The area is also very heavily wooded forest in places but the high detail DEM process seems to 'see through' the forest to the real ground level.
Good luck with whatever you decide.
PG

[schweitzerdude]

Where did you get the 30m DEMs? I am trying to make my route as accurate as possible and that may be useful.

The 30m DEMs I mention will be less detailed than what JCitron mentioned but still more detailed than the 70m DEM you tried.

I use this website: 30-Meter SRTM Elevation Data Downloader (dwtkns.com)

What it is is a user-friendly front end to the 30m SRTM (Space Shuttle) DEM from the US government. It covers all of the southern half of Canada. You will need to establish a login with NASA. Try this:

https://earthdata.nasa.gov/

Or if it's not helpful, resort to Google. Once your login is set up, you don't need to go to NASA directly ever again for SRTM data; the front-end website will do it all for you.

[Vern]

http://step.esa.int/auxdata/dem/SRTMGL1/

Could try the above, all updated to 30m DEM. Personally though I have found any route I've tried making with them has lots of small undulations where the ground should be smoothly graded or even level, so the averaging doesn't seem to be quite right.

[rs2007]

I have actually found 1m DEMs from the Canadian government's website, I also found out the hard way between the difference between DSM and DTM. They seem pretty accurate, but the problem is that they do not cover all the area I want to model, while they cover most of the GTHA, they don't cover Barrie or Niagara Falls.

[JCitron]

Does the National Map server The National Map - Advanced Viewer have anything you need? There's a bit of overlap over the border in Niagara Falls area.

[rs2007]

Does the National Map server The National Map - Advanced Viewer have anything you need? There's a bit of overlap over the border in Niagara Falls area.

It has the Niagara Falls station but that’s it. Maybe I should be more specific, by Niagara Falls, I mean the entire Grimsby Sub from West Harbour to Niagara Falls. The server does not have St. Catharines.