Rail Maps
- Thread starter conrail92
- Start date
Tracks in this screenshot look very much like the 1:24k DLG data (Digital Line Graph). DLGs are available online but require a bit of searching and preprocessing. Format for DLG is sdts and they come in 7.5 min quads, just like the DRGs (Digital Raster Graph). There is the freeware utility sdts2dxf (USGS made) which converts them to the more versatile dxf. When processing DLGs note that many are still NAD27 based. TransDEM can read DLGs in dxf format, and transform the NAD27 datum.
The question is: is it worth the effort? DLGs have been created from DRGs, i.e digitized from the raster maps, hence spacing for multiple track is just as inaccurate as on the raster maps (due to scale), curves and turnouts don't adhere to railroad track-laying rules and track layout in yards is schematic.
Often it is almost quite as fast to digitize the course of the route yourself, using the DRGs, instead of assembling the DLGs. This assumes you are using an appropriate tool, of course.
geophil
The question is: is it worth the effort? DLGs have been created from DRGs, i.e digitized from the raster maps, hence spacing for multiple track is just as inaccurate as on the raster maps (due to scale), curves and turnouts don't adhere to railroad track-laying rules and track layout in yards is schematic.
Often it is almost quite as fast to digitize the course of the route yourself, using the DRGs, instead of assembling the DLGs. This assumes you are using an appropriate tool, of course.
geophil
Hello Geophil... Your comments are very helpfull.
If you look at the map below (and above), it is smaller than 1:24 (the image is about 8/10th of a mile wide). I know it would be great if we could have the real data for it and include a dem file for that area, unfortunatly it's not available, so i have to work with what i can find...
Anyway, i overlapped an image from google earth on top of the gif i extracted before and it is quite close to reality, isn't ?
Also, i already have a tga file made from a dem (10m arc) for that region (10m arc is available for most of the Canada). Maybe i should have posted that question in your own forum, can TransDem help me laying out the tracks with such files ?
If you look at the map below (and above), it is smaller than 1:24 (the image is about 8/10th of a mile wide). I know it would be great if we could have the real data for it and include a dem file for that area, unfortunatly it's not available, so i have to work with what i can find...
Anyway, i overlapped an image from google earth on top of the gif i extracted before and it is quite close to reality, isn't ?
Also, i already have a tga file made from a dem (10m arc) for that region (10m arc is available for most of the Canada). Maybe i should have posted that question in your own forum, can TransDem help me laying out the tracks with such files ?
Last edited:
@regg001:
Unfortunately, the Canadian "Toporama" server is currently down, so here is what I could achieve in TransDEM without it:
geophil
Unfortunately, the Canadian "Toporama" server is currently down, so here is what I could achieve in TransDEM without it:
- A couple of Google Earth screenshots, georeferenced in TransDEM with GE placemarks and a few tracks, hand-sketched tracing the lines of the images.
- The Montreal area in 0.75 arc sec DEM, plus a 1:50k topo map for the top half which I downloaded some time ago. In the bottom half you can recognize the Google Earth imagery (inside the rectangular mask).
- Results in TRS2004 (just because it was quicker. TRS2006 will work as well). The mini-map:
- Track splines created by TransDEM from my humble tracing efforts.
- "UTM tile", as I call it, with GE imagery. These are flat texture carrier objects with a much higher resolution than ground textures.
geophil
Last edited: