Changes between Version 1 and Version 2 of FAQ/demtoosmall


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Timestamp:
Feb 9, 2010 10:55:22 AM (9 years ago)
Author:
benj
Comment:

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  • FAQ/demtoosmall

    v1 v2  
    2323There are a few possible solutions to this:
    2424
    25 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.
     25 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.
    2626
    27 1. 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 to affect one end of one or two flightlines (which may be beyond the area you're interested in).
    2828
    29 2. 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.
     29 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.
    3030
    31 3. Just process the entire flightline without using a DEM. This is the easiest solution, but will deform your output image (typically it will magnify the image, largely in the across-track direction) because of the difference between the real and assumed height of the ground.
     31 4. Just process the entire flightline without using a DEM. This is the easiest solution, but will deform your output image (typically it will magnify the image, largely in the across-track direction) because of the difference between the real and assumed height of the ground.
    3232
    3333[wiki:FAQ Back to FAQ]