Changes between Version 19 and Version 20 of Sensors/LeicaLIDAR/MikesNotes


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Timestamp:
Sep 1, 2008 10:34:49 AM (11 years ago)
Author:
mggr
Comment:

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  • Sensors/LeicaLIDAR/MikesNotes

    v19 v20  
    55torsion error correction
    66
    7 AGC details
    8 
    9 QC procedure (probably all in Mark's notes?)
    10 
    11 Orthophotos?  (don't think we need this, plus we don't really have enough detail.  Might just do a 2 paragraph thing)
     7
     8== QC procedures ==
     9
     10''Mark seems to have covered these better, key concepts only here''
     11
     12Essentially all using TerraScan.  The main things are:
     13 * profiles
     14   * profiles along averaged areas
     15   * profiles along a track (e.g. following a ditch / feature in the surface)
     16   * narrow profiles across features where swaths overlap
     17 * comparisons against GCPs
     18   * requires the point cloud to be converted to a surface (
     19
     20
     21== Automatic Gain Control ==
     22
     23The intensity of a return is measured (R1-R3) as an 8 bit value (0=dark (water), 255=bright) relating to the reflectivity of the illuminated surface.  The value is amplified by an automatic gain controller to keep it within 8 bit range.  The value of the AGC is also measured as an 8 bit value and is recorded per pulse as the "gain control voltage" in the raw files.  Typical values are 110-180.
     24
     25The AGC is controlled automatically in our LIDAR, but operates on a threshold basis.  If there are N (64?) low intensity points in a row, the AGC will step up one level.  If there are M (32?) overbright points in a row, the AGC will step down.  This may lead to visible steps in the image intensity, but isn't supposed to be a big problem.  Look out for streaky areas though ("contact support if you see this" - though not sure why).
     26
     27== RCD camera ==
     28
     29=== Orthophotos ===
     30
     31This apparently takes another week long training course.  We do have the basic software to do it but limited knowledge.  Basic process is to determine the camera parameters, correct and overlay the images, keeping ideally only the most central parts.  You then have to manually check through, especially along seams, and manually move the seam line in some instances (e.g. when perspective effects result in odd errors due to the seam hitting a tall building).
    1232
    1333= LIDAR processing notes =
     
    4262
    4363Streaky intensity images - "bad, contact support for guidance".  These will probably cause range errors due to the intensity variation, no idea what the cause would be as yet..
     64
     65Poor accuracy at edges - consider trimming the swath width (reduce processed angle) to cut off bad edges.
    4466
    4567=== Other error sources ===