Terrain Levels And Google Earth

[lewisner]

Hi all, in TC3 I have measured up the existing baseboards in TC3 with the intention of recreating Kirkby Stephen East station.The western side of the station fits onto the existing board but my first question is - assuming TransDEM has been used to create the board (as it clearly has) would the EXISTING ground level represent either A) The trackbed level of the station, which covers a large area, or B) The height to raoad level on the 5 arch road bridge which crosses the station.I have done a little work and assumed it was "B" but I think I may be wrong and I want to make sure before I go on. 2nd question is - How close would the ground level be to its "true" height? Finally, scaling off the station area from Google Earth the distance from the road bridge to the footbridge at the west end of the station is 961 feet but how accurate are Google Earth images?

 

[Tokkyu40]

Google Earth images are photographs and are as accurate as any photograph. The ruler tool is fairly accurate and should give you dimensions close enough that no one will notice the difference.

Claude

 

[Capt_Haddock]

I can’t really answer your question directly except to say that I faced a similar dilemma when starting my Stroud Valleys Route.

Heights in Google earth seem to work on a ten-metre grid, so railway embankments or cuttings can be ignored. I found the only way forward was locate a large flat area nearby that the railway ran over and start from that and work back to the embankment and cutting areas.

The gradient profile information in the Middleton Press series is also useful. I laid the entire track, applied the correct gradients, and checked that the heights looked feasible.

The 1:2500 scale Ordnance Survey maps have contour lines at five metre intervals, these give a good indication although I am not sure how OS heights (based on the mean high water mark at Newlyn) relate to the NASA UTM data used by Google.

As a final check, if it looks right, once you have laid some track and put in a few bridges and other landscape features it probably is right.

[FONT=&quot]Chris[/FONT]

 

[lewisner]

Thanks for that Capt Haddock! The Kirkby Stephen East site is roughly 1800 feet long by 200 feet wide, so by that logic it must be the built terrain height which means the road bridge must be sitting on top of it.The only other issue which bothered me was that the books say the gradient between KSE and Smardale rose at 1 in 77, but I have measured Smardale to KSE out and even though the gradient looks steep it works out at 1 in 140 i.e too easy.Maybe I am just too nitpicking but I don't want to get into the same pickle I did with my own route where I made loads of mistakes and it was too late to correct them.

 

[mawilson]

One caution on elevation in Google Earth: registration is suspect. Find a place with significant relief and higher resolution imagery - say the PCH north of LA or the south coast of Catalina or, for a real thrill, check some islands in the south Pacific or Caribean - you'll find ocean with altitude >0 and roads climbing the sides of mountains. I've seen errors of as much as 30 meters. It's more pronounced N-S than E-W.

 

[geophil]

As far as I know, Google Earth for the UK uses SRTM 3 arc sec for ground elevation, the very same data source the TransDEM route builder would pick.

In the screenshot below I combined the SRTM DEM with the 1:50000 O/S map. Contour lines on the map have 5 m intervals. DEM resolution is about 50 x 90 m for this latitude. The thin contour lines in the image are DEM contours, at 10 m intervals. According to these sources, Kirkby Stephen station track level is at 267m (aboutish). This is the same as as you get from Google Earth. (I can't compare with TC3 proper as my copy still hasn't arrived.)



BTW, Planning Portal has the road level of A685 at 256.2 m near the railway bridge.

 

[AndrewH]

Hi Lewisner,

The heights on the S&C baseboards will correspond to the relevant 1:25000 OS maps.

 

[stovepipe]

Hi Lewisner,

Glad to see you've made a start already.....

From info I have Kirkby Stephen East centre station track level is 655 feet (~200m) on a 1 in 183 upgrade starting back at KS East Jct. This lasts about 0.6 mile through the station, then some level and slightly uphill gradients until 1.2 miles, then the 1 in 77 kicks in to 2.2 miles, then level through Smardale itself to 2.4 miles, followed by 0.2 mile of slight down to 2.6 miles, and then 1 in 96 to 3.7 miles and then 1 in 79 to the 5 mile mark (summit altitude 889ft ~271m), all measured from KS East Jct.

Note Geophil is referencing Kirkby Stephen West elevation, not the disused Kirkby Stephen East.

Good work with Appleby East btw.

Hopefully Ben's Belah will be on DLS tomorrow.

SP

 

[lewisner]

Interesting stuff guys..."Geophil" I was panicking about what you said about the ground level at KSE until I read what Stovepipe said! There was an indepth article on Kirkby Stephen East in "Railway Bylines" magazine Volume 7 Issue 3 February 2002 and on the OS map the Benchmark level in the goods yard (trackbed height) is 653.5 feet which equates to 201 metres so the TC3 height of 190 metres is acceptably close>I have adjusted the ground level at KSE (see below) and it looks much more realistic.However there are differences between photos, the track diagram in Peter Waltons' book and the OS map so it needs further research.Got to go now, as I have a new toy (see UK Screenshots).