Changes between Version 2 and Version 3 of FAQ/demtoosmall

Timestamp:

Feb 9, 2010, 10:56:37 AM (14 years ago)

Author:

benj

Comment:

--

FAQ/demtoosmall

@@ -23 +23 @@
 There are a few possible solutions to this:
 
- 1. Extend your DEM coverage using external datasets such as [wiki:Processing/NextMapDEMs NextMap] for the UK or [http://srtm.usgs.gov/ SRTM] outside the UK. Depending on where your flight is, this may not be an option since SRTM only covers the area between 54S and 60N. If you do this, be careful about using data in the correct projection and datum (both vertical and horizontal) to match your data. !NextMap is in British National Grid projection and uses the Ordnance Datum Newlyn vertical datum. SRTM is given against the EGM96 geoid.
+ 1. Extend your DEM coverage using external datasets such as [wiki:Processing/NextMapDEMs NextMap] for the UK or [http://srtm.usgs.gov/ SRTM] outside the UK. Depending on where your flight is, this may not be an option since SRTM only covers the area between 54S and 60N. If you do this, be careful about using data in the correct projection and datum (both vertical and horizontal) to match your data. Our LiDAR data is typically supplied processed against the WGS84 ellipsoid. !NextMap is in British National Grid projection and therefore uses the Ordnance Datum Newlyn vertical datum. SRTM uses the EGM96 geoid as the vertical datum.
 
  2. Use a program such as GRASS to extrapolate DEM coverage beyond your current coverage. Gives you a DEM that is essentially completely made up for part of it, but since it's hopefully at approximately the right height (and therefore shouldn't cause significant distortion in the output), you may not mind. It may also only to affect one end of one or two flightlines (which may be beyond the area you're interested in).