Changes between Version 8 and Version 9 of Sensors/LeicaLIDAR/MikesNotes


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Timestamp:
Aug 26, 2008 3:54:28 PM (11 years ago)
Author:
mggr
Comment:

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  • Sensors/LeicaLIDAR/MikesNotes

    v8 v9  
    7070 * Pressure and temperature measurements at the plane position above the site [this affects how long it takes the laser light to move through the air]
    7171
     72== Recommendations ==
     73
     74Perform calibrations frequently at the start of the period to get a feel for how they hold.  Reduce down to fit circumstances over time.
     75
     76== Required items for processing ==
     77
     78Items required from every flight:
     79 * GPS/IMU data
     80 * Raw laser data
     81 * Logfiles from LIDAR
     82   * Flight logfiles are useful too, if the LIDAR flight planning software is used
     83 * RCD & webcam images
     84
     85Items required in general:
     86 * calibration (see elsewhere)
     87 * lever arm measurements
     88
     89= Processing =
     90== Extraction ==
     91
     92Use IPAS Pro to extract GPS, IMU and laser data from the raw files.
     93 * probably worth having the real time navigation info (doesn't add a lot of processing time)
     94 * during extraction, view the listing and verify the lever arms are correct (IMU one should never change).
     95 * look out for data gaps (listed in log)
     96
     97Most Leica systems are mounted "laser backwards" (cables will be at the rear if this is so) - ensure that z=180 in the IPAS Pro aircraft tab.
     98
     99== Navigation processing ==
     100
     101See other pages on navigation processing as they cover this already.
     102
     103
     104== Initial QC ==
     105
     106See if the lines are too short or if the point cloud has poor return %s.  If so, check the following (look at webcam images for hints):
     107 * clouds
     108 * height problem ("range gate" issue)
     109   * eyesafe shutoff (too close to ground)
     110   * too high may give dropouts
     111   * find altitude over ground (measured GPS alt - geoid-spheroid height) and see if it's within the min & max ranges
     112
     113--------------------------
     114= Calibration =
     115
     116== Parameters needing calibration ==
     117
     118Lever arm measurements:
     119 * IMU -> sensor head (centre of mirror?)
     120   * Measured in the factory and provided by Leica
     121 * IMU -> measurement point [front left corner of the casing]
     122   * Measured in factory and provided by Leica
     123 * measurement point -> GPS antenna centre
     124   * '''We need to measure this one with a survey'''
     125
     126Intensity Based Range Correction (IBRC).
     127 * A range correction based on the reflectivity of the target object ("reflections are slower on darker objects"?  perhaps this is more that a lower intensity return may take longer to be detected - ie. takes longer for enough photons to come back to exceed the detection threshold).
     128 * Measured in factory and provided by Leica.
     129
     130Range offset correction.
     131 * Correction for the slightly different timing of the 4 range cards in the system
     132 * At a set distance, the range cards should all return the same result
     133 * '''Measured by Leica but also measured and verified in calibration procedure.'''  (see below)
     134
     135
    72136== Calibration site requirements ==
    73137
     
    93157A nominal quality of 5-10cm (vertical) is suggested as a reasonable output.  If one has GCPs, it should be possible to do better (EA claims 1-2cm).
    94158
    95 == Recommendations ==
    96159
    97 Perform calibrations frequently at the start of the period to get a feel for how they hold.  Reduce down to fit circumstances over time.
     160------------
    98161
    99 == Required items for processing ==
    100 
    101 Items required from every flight:
    102  * GPS/IMU data
    103  * Raw laser data
    104  * Logfiles from LIDAR
    105    * Flight logfiles are useful too, if the LIDAR flight planning software is used
    106  * RCD & webcam images
    107 
    108 Items required in general:
    109  * calibration (see elsewhere)
    110  * lever arm measurements
    111 
    112 == Parameters needing calibration ==
    113 
    114 Lever arm measurements:
    115  * IMU -> sensor head (centre of mirror?)
    116    * Measured in the factory and provided by Leica
    117  * IMU -> measurement point [front left corner of the casing]
    118    * Measured in factory and provided by Leica
    119  * measurement point -> GPS antenna centre
    120    * '''We need to measure this one.'''
    121 
    122 Intensity Based Range Correction (IBRC).
    123  * A range correction based on the reflectivity of the target object ("reflections are slower on darker objects"?  perhaps this is more that a lower intensity return may take longer to be detected - ie. takes longer for enough photons to come back to exceed the detection threshold).
    124  * Measured in factory and provided by Leica.
    125 
    126 = Processing =
    127 == Extraction ==
    128 
    129 Use IPAS Pro to extract GPS, IMU and laser data from the raw files.
    130  * probably worth having the real time navigation info (doesn't add a lot of processing time)
    131  * during extraction, view the listing and verify the lever arms are correct (IMU one should never change).
    132  * look out for data gaps (listed in log)
    133 
    134 Most Leica systems are mounted "laser backwards" (cables will be at the rear if this is so) - ensure that z=180 in the IPAS Pro aircraft tab.
    135 
    136 == Navigation processing ==
    137 
    138 See other pages on navigation processing as they cover this already.
     162== Range offset calibration ==
     163 * Two datasets required:
     164   * BIT (Built-In Test) mode data, where the range cards are all fed with identical fake data representing the same distance.  All cards should give the same result, so differences are used to calibrate each card against the others.
     165   * A real dataset with