Changes between Version 4 and Version 5 of Sensors/LeicaLIDAR/FWMikesNotes


Ignore:
Timestamp:
Jan 27, 2010 7:07:07 PM (10 years ago)
Author:
mggr
Comment:

mucky paste to clean up

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  • Sensors/LeicaLIDAR/FWMikesNotes

    v4 v5  
    2020
    2121Some other important points:
     22 - normal lidar returns based on threshold, then look for peaks
     23  - requires a non-peak gap after a peak is found, so double peaks not spottable without  fwd
     24
     25laser pulse is 4ns pulse duration or 9ns (<100khz digitisation), so must have a <2ns intensity digitisation to avoid aliasing (nyquist), normally prefer 1ns
     26
     271ns = 15 cm
     28
     29intensity is digitised to 8bit
     30 - no range gate yet but may be added (phil)
     31 - "pre-trigger" samples = buffer before first return peak to ensure you get lead in to pulse, defaults to 5m
     32  - especially important if there's low signal before first real peak, e.g. sparse tree top
     33range data is measured independently to achieve 1.5cm range (100 picosec).
     34 - fwd data goes to RawWFD, structure identical to RawLaser, files named WFDYYMMDD_HHMMSS_XXXXXXXXXXX{AB}.LWV
     35  - A or B indicates which board digitised the signal
     36.LWV files
     37 - are always up to 62501KB
     38 - always in A&B pairs
     39 - can't link single scn files to lwv files within a flightline
     40flightline log file says if WFD on/off
     41 
     42can turn processing of waveform data off
     43always produces las 1.3 file (despite currently saying 1.2)
     44 - filename ends _4.las O_o
     45 - unless you choose las 1.0 from the output options, but you must also check the output with timestamp option
     46trigger delay settings
     47 - TPR = transition pulse rate, when the lidar changes from long pulses to short ones
     48 - for our system, >100KHz = 4ns pulse, <100kHz = 9ns pulse
     49 - each must be calibrated separately..
     50  - ie. calibration must include one above and one below TPR
     51 - possibly also temperature dependent.  shonk.
     52 - should be able to do this with bit mode data?
     53  - possible hardware issue preventing this, definite software issue (fcms doesn't record fwd in bitmode)
     54  - definite killer: timing known to verify within a flightline
     55   
     56processing time
     57 - discrete only, maybe 30secs per line
     58 - waveform data = ~10x slower
     59  - started 1023, finished 1030
     60 - approx 10x larger file (46MB without fwd and 450MB with)
     61 
     62waveform viewer
     63 - gps time = time of first return / when fwd started recording (but note it'll also have some pretrigger buffering)
     64 - retpoint loc = same time but in terms of fwd timing (?)
     65 - no way to accurately get second, third, etc times
     66
     67calibration procedure
     68 - delay between first return and trigger pulse getting to waveform digitiser
     69 - histogram viewer (lashistoviewer)
     70  - can see AGC histogram.  Looking for dataset with agc somewhere in the middle range (150 ish) and without large variations
     71 - look for data point with intensity 60-80 ish / 1V, single return
     72 - find peak time for first return visually (e.g. 22.5ns into fwd sample window)
     73 - use ret point loc (e.g. 32.766ns)
     74 - calculate delay ;p
     75 - put into trigger delay in options, see if things look better
     76 - repeat N times
     77 - repeat for dataset above and below TPR
     78 - known to vary within a flightline by a small amount (+/- 100 ps)
     79viewing with terrascan
     80 - alspp, create trj trajectory files
     81 - provide to terrascan.. next to helicopter icon under /// icon in toolbox ;p
     82  - then select file and import
     83  - terrabox, flightline -> deduce using time
     84  * possibly need to add trajectory to las 1.3?
     85 - view single point's waveform
     86  - draw in 3d draws a coloured ray, blue = low value, red = high
     87  - have to delete ray manually O-o choose selection tool, select line, delete
     88   - spectacularly poo
     89 - extract echoes (cf. calculate returns from waveform data)
     90  - place fence around, say, a tree
     91  - extract echoes
     92  - analyses waveform data and picks out a bunch of new returns, adds them
     93 - can extract data to ascii for a single point or a fence (EEK! one text file per point! NO, per {only or first+last} return!)
     94  - not sure there's a way to tie the waveform info to the return time? particularly for not-first-returns
     95  - spectacularly poo
     96 - terrascan user group meeting
     97  - 10-17 February 9th Terrasolid European Users Event, Levi Summit, Kittilä, Finland,  Internet: www.terrasolid.fi/en/events/terrasolid_european_users_event_2010_agenda_an
     98 - check out other software, fullanalyze?
     99
     100
     101
     102RCD changes
     103 - uses full CCD instead of cut down area
     104  - 7162x5389 -> 7212x5408, 7012x5208 after geometric enhancement
     105  - see presentation for depressing readout location on old setup
     106 - change to SSD
     107 - new workflow software
     108  - file renaming to flightline/project naming from fcms
     109  - distortion removal, shutter correction
     110  - DTM support, for displaying in workflow manager
     111  = big change, but we don't use this
     112  * however, we probably should as this seems to be the bit that does distortion fixups..?
     113   - not ready yet.. maybe next week
     114 - post processing sw -> 1.2
     115  - no breaker changes
     116  - minimised L/R imbalance, improved radiometric using ccd border area (hrm)
     117
     118AGC setting constant for a single pulse (ie. only need the one recorded in SCN)
     119 - confusing slide on intensity scale relating to voltage..  not quite sure what value is recorded (raw or agc scaled)
     120 - note intensity scales are different for standard returns and fwd
     121
     122things one can detect.. maybe..
     123 - pulse stretching (return pulse longer than laser pulse
     124  - slopes
     125  - low vegetation (ie. may need to adjust "ground" peak downwards a little)
     126 - indication of biomass by evaluating area under peak
     127 - better vertical resolution/distinction of objects
     128
     129angle of laser may make a difference  (flat ground at nadir is a slope at edge of fov, or cutting through vegetation)
     130
     131hardware changes
     132 - new data logger (cope with higher io)
     133  - hdd -> 160GB SSD, works up to 7620m altitude
     134   - should be ok to use spinning disk for bigger datasets @ low altitude
     135   - can't swap disks in flight without full shutdown of logger, but can keep ipas going without recording
     136 - fwd boards, 2 of them at 60kHz each
     137
     138software changes
     139 - hardware done, most software beta or not done yet
     140 - various operation changes
     141 - fcms now creates proper structure for file outputs, but only for the laser - rcd isn't done!
     142  - may change some of our naming ("WebCamImages" or something like that)
     143 - waveform viewer s/w
     144 - alspp outputting in las 1.3 type 4 (option to output 1.0 if needed for compat)
     145 - version list in presentation
     146
     147if pulse rate > 120kHz, then FWD on every second pulse..  e.g. 150kHz SCN file = 75kHz FWD
     148
     149where did gain come from in waveform viewer
     150 - volts= digitized value * gain + offset
     151 - not agc gain, this is a fixed amplication on the waveform board
     152 - value is 0.017290626
     153 - offset is also hardcoded, value is 0
     154 - system digitises from 0 to 4.something volts
     155 - gives you volts as received at the waveform board, after AGC applied, etc - probably only useful for engineering team
     156 
     157bit mode
     158 - actually could process it!
     159 - interesting underflow spike
     160 - engineering think trigger delay shouldn't change with time, but may with temperature?
     161 - not sure if bit mode vs lase mode will have a different delay, not tested
     162 - fcms will record waveform bit mode data, will in version approximately 3.2.2? probably 6 months
     163 - should ensure you have full nav solution for maximum gps timing accuracy (ie. don't just switch on ipas and record, wait a few mins first)
     164 - need two recordings for bitmode, at pulse rates above and below TPR
     165 
     166gps time difference between line time in alspp summary and waveform viewer times
     167 - Yuji checking
     168 
     169lashisto viewer
     170 - can look at las files with it, gives various useful info
     171 - drag and drop a log file into it to get nicely parsed info
     172
     173data rate / height stuff
     174 - 19.2 / 38.4 / 76.8m for various heights
     175 - 1h04 recording at max rate on 160GB SSD
     176
     177terrascan
     178 - displays waveform as colour coded line along angle of ray
     179  - can set thresholds and ranges for colour coding
     180
     181future processing
     182 - gaussian fitting to fwd data
     183 - working with vienna uni guys
     184
     185ops changes: various.. relevantish ones to us are
     186 - hardware is now licensed (ie. turns into a paperweight if expires)
     187 - closing fcms shuts the system down cleanly
     188 - need to use fpes10 for planning
     189 - automatic bit mode at start and end of fcms session
     190 - moving to ethernet comms rather than rs232
     191
     192processing changes
     193 - require alspp 2.69 or grater
     194 - GPS leverarms refer now to PAV80 rotation center (stabilised mount for camera, we don't have one)
     195  - PAV80 would be underneath the scanner
     196  * see slides for update formula
     197  * update wiki
     198  - alspp takes account of this if .sup file has a flag saying it was run with new fcms (sup comes from modern ipas pro)
     199  - lever arm measurement is the same, but you must include the offset to the virtual pav80
     200  - note this doesn't apply to IMU - this is a fixed offset and entered into fcms
     201   * check it's right ;p
     202   - fixed offset is apparently x=-0.411, y=0.206, z=-0.192
     203   - fcms also has a user defined offset currently set that is the offset from the pav80 back to the mirror
     204    - this is x=0.142, y=0.001, z=-0.188
     205    * this possibly should be zeroed - Yuji checking if having it set will cause a double offset to be applied
     206  - check lever arm error (should be small, a few cm)
     207 - new option in alspp to process waveform
     208 - trigger delay in pico secs (= splitter circuit delay)
     209  - one for 4ns one for 9ns pulse width (!)
     210  - but no difference for A & B boards.. hrm
     211 - order of 10x slower processing
     212
     213
     214IMU discussion
     215 - some discussion of IMU sharing
     216 - should be possible to mount lidar rigidly by removing shocks (or add massive stiffener!) and then applanix / ipas IMUs should be the same
     217 - not a risk of damage
     218 - interesting talk about harmonics between mirror vibration and engine vibration
     219  - IMU can pick this up and it'll show as banding alongtrack (for pitch errors) in the data
     220
     221
    22222  * Nothing has changed for the AGC/mainboard of the ALS so the raw laser .SCN files will be the same as before.
    23223  * Extra files will be created that contain the waveform data. Waveform files (.LWV) will be in the raw_wfd directory, SCN files in the raw_laser directory.