DEM Commission?

[PortLineParker]

Hi all,

I was just wondering if anybody knows of a person/site/organisation that will accept DEM commissions? I'm looking to obtain a DEM of the Bluebell Railway in Sussex, and wondered if I'd be able to commission someone to generate one.

Cheers,

PLP

 

[oknotsen]

FYI the price of the program you should consider just buying it.

 

[PortLineParker]

Hi oknotsen,

I already have the DEM software, but after numerous attempts at learning how to use it, I just can't get my head around it.

Cheers,

PLP

 

[oknotsen]

I am sorry to hear that.
Maybe some people are willing to help you with that. I think the software has a support topic in the payware section.

 

[Jayco-man]

Find the area you want to dem, and go through the tutorial. Use your area instead of what they are using. This is how I did it and it seem to work out ok. Keep trying it takes awhile to get the hang of it. Good luck.

 

[PortLineParker]

Cheers both, I'll have another go and see how I get on.

PLP

 

[Vern]

Transdem for UK routes is really easy as once you get the DEM imported, if you have the mapping server data installed you can access Sabre Maps which will give you historic OS mapping. (The modern OS feature on Live Maps no longer seems to work). At a pinch you can use Open Street Map.

On a slightly related note, you mention the Bluebell now if memory serves me correctly they are one of the preserved railways (along with Severn Valley and NYMR) who get a bit funny about being represented in a simulation product. Not sure if it was UKTS or Trainsim Dev where I read someone had encountered issues when contemplating a TS20xx (Railworks) version of the line. If the route is purely for your personal use no-one will ever know, but if you plan on eventually distributing - even freeware - might be worth contacting the railway to see what their views are.

 

[PortLineParker]

Hi Vern,

I've got something in the works so to speak, watch this space. But thanks for the tips, much appreciated.

As for the Bluebell, I emailed them a couple of years ago when I was contemplating creating a version for TS10, asking if there were any implications in modelling the line. The response I received stated that as long as it wasn't for profit, they didn't have a problem with it so all good there.

The route is intended to be hosted on the DLS, with two versions being available: Sheffield Park to Kingscote, and Sheffield Park to East Grinstead.

Cheers,

PLP

 

[scratchy]

If you figure out how to create a DEM for a UK route a tutorial would be great!

 

[geophil]

I'm looking to obtain a DEM of the Bluebell Railway in Sussex

To start with you can try O/S Open Data Terrain 50 which is a 50m grid DEM, significantly better than SRTM. But there should also be 2m hi-res LIDAR data. You can combine the two in TransDEM.
Terrain 50:
https://www.ordnancesurvey.co.uk/opendatadownload/products.html

2m LIDAR:
https://forum.transdem.de/viewtopic.php?f=2&t=392
http://environment.data.gov.uk/ds/survey#/download

To identify the DEM (DTM in brit. engl.) files you need, you will have to make yourself familiar with the O/S map grid and its code of letters and numbers, fully supported by TransDEM.

Sussex is also covered by large scale historic O/S topo maps, made available by the National Library of Scotland, both 6 inch and incredible 25 inch, easily accessed via the TransDEM Map Tile client:


If you go for the utmost detail, be aware of the amount of geo data to deal with. :hehe:

 

[anathoth71]

To start with you can try O/S Open Data Terrain 50 which is a 50m grid DEM, significantly better than SRTM.

Greetings Phil,

I was of the understanding that SRTM data has now been de-anomalied and available in 1 arc-sec (30m) resolution. Are you referring to the original 90m data in the above quote? Please advise if I am incorrect about this.

Thanks

A71

 

[geophil]

I was of the understanding that SRTM data has now been de-anomalied and available in 1 arc-sec (30m) resolution. Are you referring to the original 90m data in the above quote?

It depends where you want to build your route. For many countries orbital SRTM is still the only or the only reasonable free DEM data source, but for others, where you have terrestrial data, I would usually prefer the latter. Better accuracy, even at the same or slightly lower nominal horizontal resolution. So, when comparing 1 arc sec SRTM (30m) and 50m O/S DTM "Terrain 50", O/S will win. And with hi-res LIDAR slowly becoming available, you are in a different world altogether.

BTW, the USGS server URL for 1 arc sec SRTM has changed, it's now here:
https://e4ftl01.cr.usgs.gov/MEASURES/SRTMGL1.003/
https://e4ftl01.cr.usgs.gov/MEASURES/SRTMGL1N.003/

 

[anathoth71]

but for others, where you have terrestrial data, I would usually prefer the latter. Better accuracy, even at the same or slightly lower nominal horizontal resolution.

By how much would the accuracy be greater (assuming identical resolution) would you estimate? I mean in terms of the result on a generated DEM. Is it perceivable? I am by no means an expert, but I assume terrestrial sampling removes radar error or losses possibly caused by thick foliage, rooftops, atmospheric conditions etc.?

BTW, the USGS server URL for 1 arc sec SRTM has changed, it's now here:
https://e4ftl01.cr.usgs.gov/MEASURES/SRTMGL1.003/
https://e4ftl01.cr.usgs.gov/MEASURES/SRTMGL1N.003/

Yeah, I found this out the hard way recently, so moved over to getting 1arc-sec GeoTIFFs from the earthexplorer site. While we have the resident DEM expert on hand, may I enquire if it is correct to assume the data itself does not suffer a quality difference between .hgt and GeoTIFFs? Or that TransDEM prefers one over the other?

 

[geophil]

but I assume terrestrial sampling removes radar error or losses possibly caused by thick foliage, rooftops, atmospheric conditions etc.?

Exactly. Make the comparison yourself, visually and physically. Switch on "Interpolated DEM view" and "Shaded DEM relief" in TransDEM, for both sources. You should notice a difference, the terrestrial DEM will probably look finer. Then take few height measurements, and compare with the contour lines of a large scale official topo map, for those critical spots you mention, like built-up or forest areas.

Yeah, I found this out the hard way recently, so moved over to getting 1arc-sec GeoTIFFs from the earthexplorer site. While we have the resident DEM expert on hand, may I enquire if it is correct to assume the data itself does not suffer a quality difference between .hgt and GeoTIFFs? Or that TransDEM prefers one over the other?

Theoretically the data should be the same. However, for higher latitudes the EarthExplorer GeoTIFFs have a lower x resolution of 2 arc sec, they are packaged as nominally 2 x 1 arc sec, about 40 x 30m instead of 20 x 30m. But I am not quite sure whether you actually lose detail this way, as the real resolution is lower anyway.