TransDEM Forum

Hi guys. Im not sure if Ive just been doing things wrong or using the wrong sort of files but here's my problem. I want to map a part of my local area (UK). So I have downloaded what I think are the relevant files from Ordinance Survey. The area is designated as SO (in my particular case SO86). Inside the folder (called panorama_gb) are 2 further folders (contour and DTM). Inside of the DTM are a further 2 folders, (ASCII and NTF). Inside each of these are a further 2 folders (data and doc). Each of the data files the contains a series of folders including the one I want called SO. Ive chosen to use the ASCII data as Transdem reads the files without problem. Converting the so86.asc file produces a file called so86_t.dem
Im also using a raster file for the area. Now Ive followed the instructions for geo-referencing the rastor file and have produced 2 files called SO86_georef.png and SO86_georef.trf. This is where my problem occurs. I should not here that all files (so86_t.dem and SO86_georef.png/trf) are in OSGB36 national coordinate system format and then the georefe files are converted to UTM.
The next part of the process tell me to open the DEM file and then open the geo-ref file. At this point I get a message which tells me me the following:

UTM zone of this raster map too far away from current UTM zone to allow useful transformation.

What am I missing or doing wrong? Do I have the right type of data file to begin with? Hope someone can help me out. Thanks in advance.

Antony

I suppose, georeferencing went wrong for either of the two, DEM or raster map.

Open the two separately in TransDEM and check the coordinates in the status bar. In the TransDEM View menu, set the coordinate system to OSGB36 and enable Grid Square. Now, for both DEM and raster map, projected coordinates should start with "SO", according to your example. For the geographic coordinates the longitudes should be lower single digit degrees for the UK, since we are close to the Greenwich meridian.

Thanks. I will go back and double check it. However I have found another tutorial - which funnily enough covered the exact area I wanted to model so I have at least something to work with.
I do have another question though and I'm not sure if this is a Transdem question or Trainz. When I finally got the map up in Trainz I could clearly see where the railtrack goes. However Its also clear to me that the track is not at the right heights. Is there any way in Transdem for me to include (and find) the track heights along the route? Or is this something I will have to find and build in in Trainz?

Ok further to this problem I have the following problem. I decided to follow the tutorial for using google earth maps. I selected the map area I wanted - still based on exactly the same town as before. Opened the image as a raster map, (which I set at 5k eye height in Google earth), and proceeded to georeference the map. This all went ok. I then added the dem for that location. It opened it ok but I was totally baffled about what happened next. The dem opened in its position as SO86 as expected but the raster map had placed itself at approximately SP50. I thought that was odd so I closed both the dem and the raster map. Reopeened the dem file first then added in the raster map and got the same result.
Now either I am doing something seriously wrong or - well Im not sure what. Ive rechecked several times that according to the UK Ordinance survey maps that the town I am looking at (Droitwich), is clearly in the map grid SO86.
Its odd though that when I did the same thing but using the map tile server and the settings you have given, then they match up perfectly well. I wanted to use the raster maps as I thought they would give me better control over cuttings and embankments. Maybe Im wrong on that, I dont know. But if I try to export the track route to Trainz, using the images obtained from the map tile servers, it wont let me do anything with the settings for embankments etc as they are greyed out.
Can you help please in redirecting me as to where Im going wrong? Thanks

G'day AntonyVW,

Welcome to the wonderful world of TransdEM and Trainz...

...if I have understood you correctly, Antony, I cannot see the point of trying to do things manually, when, with the unsurpassed assistance of the Map Tile Servers, one can 'get the job done' almost automatically, which will always eliminate the 'chance' of any inaccuracies creeping into the process. I agree, it is "unfortunate" that the currently available online OSGB 'display' no longer complies with the older displays to which we are all accustomed and (it appears) no longer includes the display of embankments and cuttings in their Topographic Raster maps. As an alternative, have you tried using the "Historical" UK Map Server?...

..as far as the embankments and cuttings in the TransDEM export settings are concerned, these options are only available if the 'vector data' you are providing for the Route Polyline is 3D in nature (that is, it includes not only the regular 2D longitude and Latitude information for the location of the various points along the line but also the height information for the Elevation of said points)...

Jerker {:)}

Thanks Jerker. I eventually figured that out late last night.
Along with all the other data I got from OS is a set of files in .dxf format. They produce a wonderful array of blue lines all over the shop. When I came to export this to Trainz I found that the 3d options were now available - unfortunately I have no idea how to set them at the moment so left them at the default settings. I was not sure what to expect when I loaded up the route in Trainz, but it certainly came as a surprise that track had been placed at every spot one of those blue lines occurred. I'm sure there must be a work around but I have no idea what that is at present. So my next challenge is how to handle this side of it.
I did do some checking though at where these extra tracks had been placed and found that many of them in the small locality I tested, were not at the height of the contour lines actual map height. That did show me how Transdem has smoothed out the hills and why it was so unrecognizable in areas Im familiar with with the ground territory. Unfortunately this was no help in knowing the elevation height of the track as this will still have to be manually input. still I believe I am learning.

A quick question. Once a route has been marked in Transdem using the simple route editor, is it possible to export this into a cad program to give me an accurate route which I can them manipulate to add the correct elevations to? And then of course import it back again.

Yes, it's possible. TransDEM supports a number of vector data formats. For exchange with a CAD tool, DXF is probably the recommended format. TransDEM's knowledge of DXF is rather limited, though, but polylines should work. To make re-import possible when using DXF, you have to export UTM coordinates in their full value range (reply "no" to that message box).

Cartographic map data is usually 2D. In cartography, height (or elevation in American English) is seen as a mere attribute, not as the third component of every point. Try to get hold of CAD track infrastructure data from Network Rail. That should have it all.


While TransDEM does apply some smoothing (which can control when exporting to Trainz) the main reason for the terrain to appear less accentuated in Trainz than in nature is the DEM itself and its limited resolution. This has also been pointed out by Vern in the Auran forum. Have a look at these examples of USGS DEM data.