DEMs

[mathiasw]

Hello

I have a couple of DEM questions that you might be able to help me with...

First, I use this page as a source for my data since the NASA data doesn't cover the area I am interested in:
http://www.viewfinderpanoramas.org/dem3.html#eurasia

When I use this in Radio Mobile it says that I get a 100m per pixel resolution.
Is there any way to improve that resolution?

There is something called "Contour data" that I can download here:
http://www.viewfinderpanoramas.org/contours2.html
This data is TXT files with numbers - what do I do with them?
Can I import them in Transdem or Radio Mobile? And will they improve my resolution?

 

[Jerker]

G'day spyfrog,

Firstly, I know absolutely nothing about the program you call Radio Mobile (or whatever it is), so I will limit all my comments to TransDEM. As far as I know ALL of the files that are downloaded from the viewfinderpanoramas website are standard, compressed *.zip files of the industry standard *.hgt format (as used by SRTM, et al) that are capable of being read (and processed) IN THAT FORMAT directly by TransDEM (without having to be decompressed). Further, unless the individual files you are downloading are specifically noted as being otherwise, ALL of the these files are of 1 arcsec (30 meter) resolution. I am intrigrued by the 100m/pixel resolution that is indicated by Radio Mobile with these files, as this would indicate that the scale of the resultant image on the screen would be EXTREMELY small (are you sure you are 'reading' this scaling correctly?).

The resolution of the 1 arcsec files, in TransDEM, at least, means that the program will provide one item of datum (elevation) for every 30 meter square area of ground. This IS AS GOOD AS YOU CAN GET for anywhere around the world, outside of the 'Continental' United States (whose government provides their elevation data - free of charge, mind you - at 1/3 arcsec resolution , where-as the rest of us must pay dearly for such data from our respective governments). It is certainly possible to alter this resolution in TransDEM (using the Grid Width option in the "SRTM & Info Parameters dialog box") but as I am not in the habit of doing so, I do NOT know the consequences of such action (perhaps Roland may step in here with a more technical explanation of the mechanics of this option in the program). Anyway, I would certainly be happy with the resolution of these DEMs AS THEY STAND.

Given the ease of using the above type files, I would steer clear of the *.txt contour files that you mention. Besides, I don't think that TransDEM is capable of reading them (again, I turn to Roland for guidance, here)..

Jerker {}

 

[mathiasw]

Thanks for your reply, mate. ;-)

The reason that I wounder about this with the resolution isn't that I think that the height is to low actually - I have more of a problem with the maps.
As you know, you can get the DEM tools like Hog and TransDem to add a map on top of the ground when they generate it.
However, when I do this, the resolution of the map is so bad that it is rather useless. I thought that this was connected to the DEM data but perhaps that is a parameter that can be changed or is it a Trainz limitation?

 

[geophil]

May I assume that you were trying the MicroDEM/HOG process? The manual steps required with this approach are somewhat error-prone. Obtaining correct horizontal and vertical resolution are in the user's sole responsibility here. You have to follow the tutorials very closely - or switch to a program that provides more automation.

 

[mathiasw]

May I assume that you were trying the MicroDEM/HOG process? The manual steps required with this approach are somewhat error-prone. Obtaining correct horizontal and vertical resolution are in the user's sole responsibility here. You have to follow the tutorials very closely - or switch to a program that provides more automation.

I see where you are coming with this geoPhil. I actually have a TransDEM licens so I will try to understand how to use it. :hehe:
Is there some kind of waltkthrough for TransDEM besides the manual somewhere?

 

[geophil]

Processing .hgt data in TransDEM is straightforward.

Step 1: Download the file(s) you need, SRTM or Viewfinder Panorama, open in TransDEM, accept the default resolution value proposed, save.

If there is more than one DEM file, merge the saved files (.dem) with the Add DEM function.

If you are not sure which files to download, do step 2 before step 1. With geo-referenced raster maps loaded, TransDEM will display hgt file names of the area. TransDEM main menu: File/DEM | File name info SRTM hgt.

Step 2: Continue with raster maps and vector lines. For an easy start, follow the Map Tiles tutorial on page 130 (current version) in the TransDEM main manual.

Step 3: Export to Trainz. Tutorial page 41 (current version), TransDEM Trainz manual.

 

[mathiasw]

Processing .hgt data in TransDEM is straightforward.

Step 1: Download the file(s) you need, SRTM or Viewfinder Panorama, open in TransDEM, accept the default resolution value proposed, save.

If there is more than one DEM file, merge the saved files (.dem) with the Add DEM function.

If you are not sure which files to download, do step 2 before step 1. With geo-referenced raster maps loaded, TransDEM will display hgt file names of the area. TransDEM main menu: File/DEM | File name info SRTM hgt.

Step 2: Continue with raster maps and vector lines. For an easy start, follow the Map Tiles tutorial on page 130 (current version) in the TransDEM main manual.

Step 3: Export to Trainz. Tutorial page 41 (current version), TransDEM Trainz manual.

I looked on the Gisa made tutorials and they are very good. However, I can't get vector data for my country so I skip that part.

I managed to get a map (from Openstreetmap) in as a texture on the ground and so that I saw it in the mini map. This meant that I used the Map Tile Server function as Gisa used the WMS server. I can't find any good WMS server to use so I have to skip that part.

In the tutorials so does Gisa download images from Google Maps and then export these as UMTs tiles. He then zooms in to level 19 in zoom.
Sadly, Google Maps don't have coverage at more than zoom level 12 for orthomaps where I am building.

So I would like to zoom the Openstreet map in to about 19 and export this as UMTS instead. But I can't do this. I think this is because the Map Tile servers is used for the purpose that the WMS server was used in the tutorial.

Is there a way to use the Map Tile server BOTH for UMTS and texture creation?

 

[geophil]

You can use the same Map Tile service for both ground Textures and UTM tile textures but you should different scale, i.e. zoom levels.

For the ground textures zoom level 14 will be adequate for a 10 m terrain grid. You can also try zoom level 15 with the 5m grid but I am afraid the minimap may suffer.

For UTM tiles zoom in closer. Maximum for Open Street Map is 17. Use that for maximum sharpness or 16 to save memory.

However, there is no need for UTM tiles to cover the entire route. If the ground texture map carries all the information you need, skip producing UTM tiles for such areas.