TransDEM Forum

Hello all!
Just wondering how and if anything was wrong with my process of setting up the route. My desires is to use Google Earth to create a DEM of a route for Trainz Simulator 2012 that is prototypical set in Illinois. I went through the tutorial about how to do this. I got the snapshot into TransDEM and got the image geocached. Beyond that I imported SRTM data from the USGS and then narrowed it down to a test area with topography I am familiar with. Trouble was, when I got into Trainz, the Google Earth image and my route I created was successfully textures, but the topography was far too hilly. I understand this area has ditches and a few crests, but the area of the railroad interlocking is as flat as a pancake with little to no grade. In game it is a literal roller coaster of unbelievable gradient. I have images from the area and compared them for hope I had perceived it incorrectly, but yes, it is a small grade, but we are talking about something spaced over the length of quarter miles, not yards!

Is there something I am doing wrong and is it possibly bad data? If it is either, how would I rectify this for an accurate DEM generation?

Thank you!

Cheers,
Joshua

G'day Santfebuff,

...it is unlikely, Joshua, given that your data is sourced from Google Earth and the USGS that it is 'wrong'. It sounds to me, without being able to see any of your images (they failed to show up in the post), that you have downloaded the DEM data Tile for the wrong Topographical area you are 'using'. This is a common error made by newcomers to this 'activity'. If you did not use the "File name info SRTM,hgt" option from the File/DEM menu to check which SRTM Tile to obtain (but, instead, guessed it from the geographical line data shown in your TransDEM window), then you will have definitely made a mistake. Because the SRTM DEM Tiles are named by the coordinates of their South West Corner and start at "1N" (or "1S", if you are in the Southern Hemisphere) and the Equator is "0 degrees" latitude, you MUST add the value "1" to the geographical display shown in the TransDEM window (the aforementioned 'option' automatically does this for you in it's "output"). So, if, for example, the coordinate lines for North 25 degrees and west 70 degrees appear in your TransDEM window, then you must needs download the DEM tile for N26W70, in order to get the correct tile for that area...

...if you have done this (and are sure the DEM Tile is the correct one), then we will need to see your images to proffer any other possible causes of your problem...

Jerker {:)}