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PostPosted: 10 Dec 2019 06:37 
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Joined: 25 Oct 2014 17:59
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Hi,

Can anyone tell me if TransDEM can produce a DEM and vector overlay for this resource: http://www.railmaponline.com please?

If so will it draw the railway line overlays over the Satellite view? This would be a very useful tool.
Many thanks
Paul


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PostPosted: 10 Dec 2019 13:42 
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Joined: 05 Jan 2011 16:45
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You can extract vector data from Open Street Map (OSM) via JOSM. See this tutorial:
viewtopic.php?f=6&t=158
A number of TransDEM users have applied this method successfully.

The map you are referring to appears to be based on Google, not OSM, so probably very different and only possible if the overlay vector data has open access.


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PostPosted: 14 Dec 2021 19:17 
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Joined: 01 Sep 2016 00:07
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Paul,

Thanks for sharing the website. Looking at a few of the abandoned lines that I've worked on which the tracks have been removed, it seems to me that the poly lines are drawn in using a best guess. I believe that you will need to reposition the track in Surveyor to adjust the grades. It will be less of a problem if you aren't modelling mountainous terrain.

It seems to me that you could do as well using TransDEM and georef raster maps plus any historical sources you can find.

good luck,
Dave


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PostPosted: 20 Jan 2022 20:15 
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Joined: 01 Sep 2016 00:07
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geophil,

Thanks for the tutorial on installing JOSM and instruction on how to use that to transfer data from Open Street Maps to TransDEM. Being able to do that for a railyard saved me days of struggling with paths and polylines. I'm a slow learner, but everything worked when the directions were followed.

(tutorial/instructions: https://forum.transdem.de/viewtopic.php?f=6&t=158 )

The polylines imported with an offset that caused the yard to be mislocated by dozens of meters. Fortunately, I've previously experimented with editing the polyline .str files and with trial and error was able to resolve the offset by changing the values in lines 8 and 9 of the .str file.

Thanks again for TransDEM and for the excellent tutorials and support!

OddRails/Dave


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PostPosted: 23 Jan 2022 15:54 
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Joined: 05 Jan 2011 16:45
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OddRails wrote:
The polylines imported with an offset that caused the yard to be mislocated by dozens of meters.
This would typically mean that the underlying geodetic datum is incorrect. But OSM uses WGS84, nothing you can normally mess with. Are you sure your DEM or raster map is georeferenced correctly?


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PostPosted: 18 Feb 2022 03:48 
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Joined: 01 Sep 2016 00:07
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I may not have had everything aligned correctly.
My edits in the .str file brought the poly lines in line with the DEM terrain.


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PostPosted: 18 Feb 2022 14:09 
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Joined: 05 Jan 2011 16:45
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Well, you could do that. But I think this will make it worse. It may look aligned now, however, all your geo data will probably be misplaced after that. TransDEM retains a static mapping between UTM coordinates and baseboards. This allows seamless merging of routes, if both are are based on TransDEM geo data. This can only work, of course, if the geo coordinates are not fiddled with.

So I would try to find the reason for the misalignment and try to fix it where it started. And that has most probably to do with georeferencing of one of your sources.

We usually have three geo data sources here: DEM, raster maps, vectors. What are your resources for those? I understand your polylines originate from OSM, via JOSM. A georeferencing error here is quite unlikely. But where do the other two come from? And between which of the three sources do you see the discrepancies?


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PostPosted: 25 Feb 2022 06:47 
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Joined: 01 Sep 2016 00:07
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Usually I get my DEMs and rastermaps from USGS The National Map client here in the USA. Often using the 1/3 arc-second DEMs. I try to be very careful arranging the mask to remove the geopdf borders, usually magnifying the map to carefully place the mask corners. Of course I use the convert to UTM function before saving.

Until OSM/JOSM, I was hand drawing tracks/poly lines on the rastermap. I still hand draw the tracks between cities.

It is possible that I might be clicking the mouse when I shouldn't on the OSM/JOSM map window. Once I accidentally copied the rail yard twice with an offset between them and waited until after exporting into Trainz 2012 to delete the extra yard segment by segment.

As long as I can figure out how to edit the tracks to line them up with the DEM, I'm relatively happy.


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PostPosted: 25 Feb 2022 09:24 
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Joined: 05 Jan 2011 16:45
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Quote:
Usually I get my DEMs and rastermaps from USGS The National Map client here in the USA.
So, DEMs in this case will be correctly aligned. With GeoPDF we have to be a bit more careful. I have encountered a few where georeferencing was wrong, for various reasons. Georeferencing parameters are part of the GeoPDF meta data. One possible mistake is the geodetic datum. While it should be NAD27 I found NAD83.

As you work with USGS 1/3 arc sec DEMs, you can usually verify your raster map, at least in hilly terrain, with the contour lines, or by turning on DEM shading. Map and DEM must match. Or create an overlay with the map tile client, and use OSM as the tile server.

Then, if DEM and raster map are in sync, and the vector input from JOSM is not, it's quite clear that something went wrong with the JOSM data. And that must have happened in one of the stages of the transfer workflow, because the OSM base data will be correct.


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PostPosted: 25 Feb 2022 18:46 
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Joined: 01 Sep 2016 00:07
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Thank you. I had not even thought of checking the NAD27/NAD83 specification with the USGS GeoPDFs. I'll try using the OSM tiles if they are more consistent with the NAD27 specification.

I'm not the most sophisticated TransDEM user. I love the ability to import terrain into Trainz, it has made a huge difference in my enjoyment of Trainz. I should do more work in TransDEM to assure better results. Often I just blunder through and try to fix everything in surveyor.


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