TransDEM Forum

TransDEM News, Support, Hints and Resources
It is currently 21 Nov 2018 14:06

All times are UTC + 1 hour




Post new topic Reply to topic  [ 16 posts ]  Go to page 1, 2  Next
Author Message
PostPosted: 12 Nov 2015 18:50 
Offline

Joined: 05 Jan 2011 16:45
Posts: 1113
A practical example for the new 2m LIDAR DEMs (see here).

You download the files from the Environment Agency website:
http://environment.data.gov.uk/ds/survey#/download
As most UK geo data they are organized by grid squares. (As an adept TransDEM user of British data you will certainly know that TransDEM can display the grid square code – two letters plus shortened eastings and northings – in the status bar.)

For my example I chose grid square SD92, Todmorden, Upper Calder Valley, West Yorkshire, with the Rochdale Canal and the “Manchester and Leeds Railway”, later becoming the “Lancashire and Yorkshire”, passing through. I prefer to pick locations for my experimenting I have visited myself and I came up here by narrowboat in 2009.

The first screenshot shows the 2m DEM for my project, about 6km long and 2km wide. Even at this rather low display scale you can clearly depict the railway line with its embankments, cuttings, tunnels and bridge gaps. (Click on the image for full size.)

Image


The 2m files are packaged as 1 x 1km, identified by grid coordinates. To find my way around I loaded an O/S Open Data 1:25000 “District” map for SD92 in the background (next screenshot below). I opened all LIDAR files I needed individually and saved the in TransDEM's .dem format, hereby automatically converting them to UTM. Using the “Add DEM” function I stitched them together to obtain the DEM shown in the first screenshot above.

Image


LIDAR coverage is limited. It concentrates on areas of cultivated land, largely untouched nature is left out. For our purposes we should fill-in on LIDAR, to avoid holes in the Trainz terrain. I will resort to O/S Open Terrain 50, the 50m terrestrial DEM, also available for free.

However, the standard “Add DEM” function in TransDEM cannot be used for filling in holes. When the “Add DEM” function merges two DEMs, it uses values from both sources for overlapping areas and computes an average. In our case, where O/S Terrain 50 also covers the same area as the LIDAR data, but at much less resolution, it will actually smooth the terrain, hereby giving away some of the crispness of LIDAR.

Therefore I have added a slightly modified “Add DEM” function to upcoming TransDEM 2.6 and named it “Fill up DEM”. When using the new function, the DEM added will only substitute the holes in the first DEM and never modify an existing elevation value. For this to work, both DEMs should have similar elevation values. Filling-up with orbital SRTM or ASTER will probably not be a good idea.

The next screenshot shows the result of filling up with the 50 m DEM. You can make out the larger 50x50 m DEM squares in the outer ranges and you can also depict the seams where the two DEM sources join. The shaded relief mode in TransDEM is rather merciless here, but these faults will appear much less prominent in Trainz.

Image


The following screenshots are all taken from T:ANE Surveyor. The first two in the series with the bare-bones DEM.

Most noticeable is the railway. The Calder River bed is also clearly visible.

Image


It is not as crisp as in the TransDEM screenshots. This is because the minimum terrain vertex spacing in Trainz is 5m, not 2m as in the LIDAR source.

But it's so far better than the 50m spacing of O/S Terrain 50, as seen in the foreground in the next screenshot.

Image


Let's add a map overlay, the historical 1:25,000 for the next image. Todmorden station. If you are familiar with the location you will identify the high retaining wall separating the newer railway from the older canal just west of the station (coming towards us in the image, right of the compass)

Image


Three screenshots with 3D UTM tiles, the tiles also as a 5m grid. The map for these is the historical 6 inch series (1:10,560). Scanned from old paper sheets it comes out a bit yellowish.

First the Calder Valley with the railway embankment and bridge gaps.

Image


Then, Todmorden station again and the retaining wall, just right of the compass.

Image


Finally, further up the valley, where the railway crosses the valley on an embankment and the canal passes under it.

Image

Compare this last screenshot with the real world, a photo taken from almost the same spot with a similar angle (in pouring rain in spring 2009). Some of the details you will be able to identify in the Trainz scene are the railway bridge over the canal (as a gap), the one over the road , the two locks in the canal, the road up the hill below (compass) or the (wooded) steep cliff in front of the church spire.

Image


Remember, this is all achieved automatically, not a single Trainz ground vertex has been touched by any Surveyor tool so far. Admittedly, it's not perfect, the embankments will need some refinement, bridges need to be placed, etc. Route building skills are still needed. ;)


Top
 Profile  
 
PostPosted: 12 Nov 2015 21:02 
Offline

Joined: 22 Nov 2011 07:09
Posts: 33
Location: Karuah, NSW, Australia
Cannot wait to have the update as I am not doing anything in Tane at present until such time as I can have access to the improved data.. I will need to rebuild my extensive route from scratch to obtain the latest DEM details and the 100 year old mapping.
Are we going to have a Christmas present from you with the release of ver2.6.


Top
 Profile  
 
PostPosted: 14 Nov 2015 12:49 
Offline

Joined: 08 Apr 2015 04:30
Posts: 7
I have downloaded a selection of the LIDAR 2M files, they download as .zip files and when opened show as Adobe Flash Files. Is it possible to provide a breakdown of the process to convert these files to the TransDEM format, as this is not clear from your post.
Thank You
Keith


Top
 Profile  
 
PostPosted: 14 Nov 2015 13:37 
Offline

Joined: 05 Jan 2011 16:45
Posts: 1113
Download the zip file(s) and unpack. You'll get a lot of .asc files, named by grid square. In TransDEM, open them as DEM files. TransDEM will recognize the format (provided you have a fairly recent version of TransDEM) and ask for the coordinate system. Set to OSGB36 (or set to OSGB36 from the main menu, with geo data opened).

The data format is the same as with O/S Terrain 50 or the former O/S Landform Panorama.


Top
 Profile  
 
PostPosted: 14 Nov 2015 15:13 
Offline

Joined: 08 Apr 2015 04:30
Posts: 7
Thanks Roland

Keith


Top
 Profile  
 
PostPosted: 04 Dec 2015 17:17 
Offline

Joined: 03 May 2012 18:09
Posts: 26
Location: High Peak Derbyshire UK
I am looking forward to the new version with fill DEM. I have been playing around with the LIDAR files which I think are great, the problem I have is there are blank spaces on my route as it is in the country. Roll on new version.


Top
 Profile  
 
PostPosted: 04 Dec 2015 19:36 
Offline

Joined: 03 May 2012 18:09
Posts: 26
Location: High Peak Derbyshire UK
This may be of interest to anyone looking at the Lidar maps.
When you have extracted the zip file you downloaded you end up with a lot of DEMs. If you are not sure which to use go to
http://www.geograph.org.uk/browse.php Where you can enter the grid reference and see a small map of that area. This helps if you do not need them all.
Lorraine


Top
 Profile  
 
PostPosted: 05 Dec 2015 18:11 
Offline

Joined: 03 May 2012 18:09
Posts: 26
Location: High Peak Derbyshire UK
I have followed the example and used SD92 but my DEMs are no way as detailed as yours, I cannot make out railway line and bridge gaps. etc. Am I missing something. I have the latest version.

Lorraine


Top
 Profile  
 
PostPosted: 05 Dec 2015 19:57 
Offline

Joined: 03 May 2012 18:09
Posts: 26
Location: High Peak Derbyshire UK
Just found out I needed shading option. :oops:
Ah well, we live and learn.
Lorraine


Top
 Profile  
 
PostPosted: 05 Dec 2015 22:03 
Offline

Joined: 05 Jan 2011 16:45
Posts: 1113
ganmar wrote:
Just found out I needed shading option.

Good to hear. I always find it amazing how this little feature accentuates details, simply by amplifying differences between adjacent points.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 16 posts ]  Go to page 1, 2  Next

All times are UTC + 1 hour


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to:  

Imprint & Privacy

Powered by phpBB® Forum Software © phpBB Group