Changes between Version 3 and Version 4 of Sensors/LeicaLIDAR/MashUp


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Timestamp:
Sep 24, 2008 5:18:07 PM (11 years ago)
Author:
mark1
Comment:

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  • Sensors/LeicaLIDAR/MashUp

    v3 v4  
    4040 * altitude (kinda a parameter ;) ) - minmium of ~650 up to ~2000m (after 2km, you start getting poor returns on forests, etc, the real limit is up to about 6km in ideal conditions)
    4141 * ... pulse frequency, scan angle, etc [TBD]
     42
    4243
    4344
     
    305306Other GCPs (number?) should be scattered around a wider area within the full swath width - typically run at 45 degrees [=620m wide on ground @ 750m alt] or to a max of 75 degrees [=1150m], though 75 degrees will introduce more errors..
    306307
     308
    307309== Quality, accuracy, etc ==
    308310
     
    311313
    312314------------
    313 
    314 == Range offset calibration ==
    315 
    316 Range offset correction (+range card calibration) is to correct for the slightly different timing of the 4 range cards (R1-R4) in both banks (A & B) in the system, and to correct any overall ground offset.
    317 
    318 Two datasets are required:
    319  1. A real dataset with:
    320    1. a source of multiple returns, such a forest (for step 1 below)
    321    1. a strip with well known distances (for verification)
    322  1. BIT (Built-In Test) mode data, where the range cards are all electronically 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.
    323 
    324 First, we need to determine the timing differences between the 4 range cards (R1-R4) in each bank.  To do this, we use a dataset with multiple varying returns present - we need combinations of 2-4 returns (forests are good for this, being tall and porous enough to give multiple returns).  When there are less than 4 returns, R4 is a second measurement (not a copy of) of the last pulse - i.e. if there are 2 returns, you will have R1, R2 and R4 (= re-measurement of R2).  This is exploited to compute the difference in timing between R2 and R4 (averaging many 2-returns).  Similary 1-return and 3-return pulses are used to measure R1-R4 and R3-R4 differences.  The end result is a set of timing differences between all the cards in a bank.
    325 
    326 Second, we need to establish the timing differences between bank A and bank B.  As with the first step, we need the timing cards to measure exactly the same instant.  To do this, we use BIT mode data, where R1 in both bank receives the same electronically generated pulse at the same instant and are thus measuring the same event.  Averaging these numbers gives the timing offsets between the R1 cards, which can be combined with the first measurements to establish timing between all cards.
    327 
    328 ''PROCEDURE:''
    329 
    330 Can do range correction if the boresight results are good. This is a 2 stage process:
    331 
    332  * 1. Nominal offset determination A1
    333  * 2. Define relative differences for A2,A3,A4 and B1,B2,B3,B4
    334 
    335 points have approx. the same range error within +/-7 degrees of Nadir, so we look only at this region firstly.
    336 
    337  * In ALSPP filters dialog set the angles to +7 and -7 degrees, change the output directory (to 02a_Roff+-7deg if using suggested directory structure) and run the processing on the 4 low altitude flight lines.
    338  * Load the results into TerraScan and use the 30-40 GCPs of the calibration site.
    339  * Tools -> Output Control Report
    340  * Browse -> GCP file and remove bad points (maybe an error occurred in the surveying of a certain point)
    341  * Look at the dz value, the average dz is used for the nominal range offset A1.
    342  * Save the text file.
    343 
    344 Preferably using data including areas of forest and the BIT mode data, run RangeCardCal (from ALSPP tools menu) and enter the average dz value as A1 to get the other offsets. Add the outputs to the ALSPP dialog and save the settings reg file (to a new name)
    345 
    346 To check these results re-run using the full FOV (~45 degrees) and check average dz is less than 1cm or so, and standard deviation <5cm in TerraScan control report. (also look at cross sections)
    347 
    348 Then process the 4 high altitude flights in ALSPP and check in TerraScan (around nadir and swath edges)
    349 
    350 Finally load in all flights into TerraScan (within a fence if memory issues) and check them (ideally along a stream because this has a “good” profile) Can use the travel path tool in TerraScan for comparing cross sections along a path.
    351315
    352316= Boresight calibration =
     
    404368
    405369This shouldn't need to be done with newer LIDARs, but included here in case.  Leica suggests checking for torsion errors if there seem to be problems in the boresight calibration and reporting to them if found.
     370
    406371
    407372Visible sign of torsion error is a smile effect.
     
    495460   * Try to include some on slopes(?)
    496461
     462== Range offset calibration ==
     463
     464Range offset correction (+range card calibration) is to correct for the slightly different timing of the 4 range cards (R1-R4) in both banks (A & B) in the system, and to correct any overall ground offset.
     465
     466Two datasets are required:
     467 1. A real dataset with:
     468   1. a source of multiple returns, such a forest (for step 1 below)
     469   1. a strip with well known distances (for verification)
     470 1. BIT (Built-In Test) mode data, where the range cards are all electronically 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.
     471
     472First, we need to determine the timing differences between the 4 range cards (R1-R4) in each bank.  To do this, we use a dataset with multiple varying returns present - we need combinations of 2-4 returns (forests are good for this, being tall and porous enough to give multiple returns).  When there are less than 4 returns, R4 is a second measurement (not a copy of) of the last pulse - i.e. if there are 2 returns, you will have R1, R2 and R4 (= re-measurement of R2).  This is exploited to compute the difference in timing between R2 and R4 (averaging many 2-returns).  Similary 1-return and 3-return pulses are used to measure R1-R4 and R3-R4 differences.  The end result is a set of timing differences between all the cards in a bank.
     473
     474Second, we need to establish the timing differences between bank A and bank B.  As with the first step, we need the timing cards to measure exactly the same instant.  To do this, we use BIT mode data, where R1 in both bank receives the same electronically generated pulse at the same instant and are thus measuring the same event.  Averaging these numbers gives the timing offsets between the R1 cards, which can be combined with the first measurements to establish timing between all cards.
     475
     476''PROCEDURE:''
     477
     478Can do range correction if the boresight results are good. This is a 2 stage process:
     479
     480 * 1. Nominal offset determination A1
     481 * 2. Define relative differences for A2,A3,A4 and B1,B2,B3,B4
     482
     483points have approx. the same range error within +/-7 degrees of Nadir, so we look only at this region firstly.
     484
     485 * In ALSPP filters dialog set the angles to +7 and -7 degrees, change the output directory (to 02a_Roff+-7deg if using suggested directory structure) and run the processing on the 4 low altitude flight lines.
     486 * Load the results into TerraScan and use the 30-40 GCPs of the calibration site.
     487 * Tools -> Output Control Report
     488 * Browse -> GCP file and remove bad points (maybe an error occurred in the surveying of a certain point)
     489 * Look at the dz value, the average dz is used for the nominal range offset A1.
     490 * Save the text file.
     491
     492Preferably using data including areas of forest and the BIT mode data, run RangeCardCal (from ALSPP tools menu) and enter the average dz value as A1 to get the other offsets. Add the outputs to the ALSPP dialog and save the settings reg file (to a new name)
     493
     494To check these results re-run using the full FOV (~45 degrees) and check average dz is less than 1cm or so, and standard deviation <5cm in TerraScan control report. (also look at cross sections)
     495
     496Then process the 4 high altitude flights in ALSPP and check in TerraScan (around nadir and swath edges)
     497
     498Finally load in all flights into TerraScan (within a fence if memory issues) and check them (ideally along a stream because this has a “good” profile) Can use the travel path tool in TerraScan for comparing cross sections along a path.
     499
     500
    497501=== Final validation and fine tuning ===
    498502