Digital Elevation Models – OS OpenData to SketchUp : A workflow

Update: Geolocating the DEM in SketchUp has been solved see at bottom of page!


So you have SketchUp and you’ve heard wondrous things about the UK’s Ordnance Survey OpenData?!    In particular you hear there maybe some contour/elevation models out there for free as well!   This quick workflow guide shows you how get that elevation model into SketchUp so you can plan horrible developments in undeserving places (I’m a planner so I know…).

Prerequisites:

  1. Windows Vista (I’m sure XP, Windows 7 etc.. all work as well)
  2. SketchUp Pro (although you can import DEMs with the free version) http://sketchup.google.com/intl/en/product/whygopro.html
  3. MicroDEM – follow the install guide to get yourself up and running http://www.usna.edu/Users/oceano/pguth/website/microdem/microdem.htm
  4. OS OpenData, in particular the Land-Form Panorama dataset, select the download option enter your details (it only requires your email address) and then wait for  523MB zip file to download https://www.ordnancesurvey.co.uk/opendatadownload/products.html
  5. Google Earth (to check your DEM is georeferenced properly)
  6. You need a basic working knowledge of MS Windows, SketchUp and some file management skills. 

Once downloaded you need to know what OS Grid square you want to import.   You can read the wiki article or I have used StreetMap and once you’ve searched for your location you can look just below the map and it says “Click here to convert coordinates” on this page LR seems to relate to the OS grid.
http://en.wikipedia.org/wiki/Ordnance_Survey_National_Grid


The Walkthrough

Double click on the ‘panorama_gb.zip’ file and navigate to this directory ‘\DTM\ASCII\data’.   Yes there are other types of data (contours as DXF and DEM as NTF) but this is what worked for me.

1 – Extract a tile from the directory name corresponding to your chosen OS tile.  In this case we’re going to use Sedbergh, Cumbria tile which is under ‘\DYM\ASCII\data\sd\sd68.asc’.  You can copy it to any directory but in this instance I tend to copy it to the ‘mapdata\DEMs’ directory created by your installation of MicroDEM (you did install it right?)

2 – Load up MicroDEM and then click File –> Open DEM now navigate to the ‘mapdata\DEMs’ directory and select the ‘sd68.asc’ file.

3 – MicroDEM will ask you to pick its projection parameters as its OS OpenData my guess is that these settings are okay and then click ‘Mercator’ instead of ‘OK’

4 – The DEM should load up and look something like this :

Nice Colours?

5 – If you want to get rid of the legend and scale bar and any grid that may appear right click on the image and select ‘Legend/marginalia’.  Uncheck the boxes and click the ‘Grid’ button and select the option ‘neither’

6 – Click ‘OK(Close’ and say ‘yes to redraw… I often get errors and warnings at this point which I ignore….
Now click on the menu heading file again and save this as a DEM and in particular a USGS ASCII one:

7 – Once it is saved close MicroDEM and open up SketchUp…  I’m assuming you will import into a fresh new SketchUp Model, so click on the File menu and select import.

8 – Choose the file type DEM (*.dem, *.ddf) and find that file you saved in MicroDEM, before you click open click on Options:

9 – Here you can see I’ve entered 20000 points to import the lower the number the less detail for this tile 20000 as suggested by Chris Fullmer’s tutorial seems good.  I suggest you experiment with this to get what you want though!  Also I’ve check ‘Generate gradient texture’ this is entirely up to you, I suggest you first try with and then without.

The DEM should be imported and the axes, click the zoom extents button to check it’s all there:

10 – Now to get rid of all those lines, double click the DEM (to edit component) and select all of the DEM (keyboard shortcut : ‘ctrl-a’).   Now right click the selected DEM and  click on ‘Soften/Smooth Edges’:

11 – As per Chris Fullmer’s suggestion slide to around 90 degrees and check both boxes (Smooth normals and Soften coplanar)

12 – Et voila! You now have a terrain model for placing your models on!

mmm smooth elevation model!

13 – One important thing to note this is not GeoReferenced.  I haven’t figured out why SketchUp doesn’t load the DEM in the correct place.  If anyone has any suggestions please tell me (via Twitter or otherwise) and I’ll add it to this tutorial.

Geo-Reference (or Geo-Locate) your DEM

14 – First you need to know where your DEM is in Latitude and Longitude you can do this by going to nearby.org Coordinate Convertor and putting in your OS tile number (in this case SD68), I suggest you select output as Coordinate Conversion only:

15 – You are now going to copy the Lat and Long coordinates into SketchUp so leave this webpage open and….

16 – In SketchUp click on the menu ‘Window’ then ‘Model Info’ and select ‘Geo-Location’

17 – Give the Country name and location something meaningful…. and copy and paste your latitude and longitude’s full number (and letter after) in the appropriate places.
Now to test it press the Preview in Google Earth button:

18 – If you’re computer is up to it you should see the DEM appear in the correct location in Google Earth, it may take a while to load though so be patient!

DEM Placed in GE