Changes between Version 4 and Version 5 of FAQ/demtoosmall


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Timestamp:
Feb 9, 2010 10:59:30 AM (9 years ago)
Author:
benj
Comment:

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  • FAQ/demtoosmall

    v4 v5  
    2525 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. It should also be used with caution for data covering areas with rapid height changes such as glaciers, since the data itself may be out of date.
    2626
    27  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).
     27 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 affect one end of one or two flightlines (which may be beyond the area you're interested in).
    2828
    2929 3. Use the -l option to azgcorr to not process one end of the affected line(s) - see part 2 [wiki:FAQ/processingspeed here] for instructions for how to do this. You can then process the area within your DEM, and then if you want you can process the remaining part separately without using a DEM.