Elevation errors

[Redford1998]

I'm experiencing problems where there is no elevation change is appearing in some areas. For example there is areas where the road is a lot lower than the rails but there is no change. Is there something i have to do to see this, any help would be appreciated

[geophil]

Where is your route project located and what kind of DEM data source are you using?

[Redford1998]

The route is located in western New York and I'm using 1/3 arc IMG DEMs from the USGS national map viewer.

[geophil]

I am not quite sure what the USGS policy is about man-made structures and their representation in NED DEMs. Mostly you'll find cuttings, high fills, ramps and abutments in 1/9 arc sec and often in 1/3 arc DEMs as well. Dams and causeways may even be found in 1 arc sec resolution. On the other hand, I have also seen 1/9 arc sec DEMs without apparent signs of transportation infrastructure.

Do the 1/3 arc sec DEMs of your project show cuttings, ramps etc at other places? If yes, could the missing features be the result of outdated data? A new highway, a new rail alignment?

[Redford1998]

The DEM is from 1998 but pretty much every thing has been there. There little to no elevation difference between rail, road and other infrastructure where there should be and I tried the 1 arc sec but its the same too. However the rail elevation seems to be accurate so maybe I just need to manually do the roads and other infrastructure.