Scanner Angle Min Max and Pulses per Scanline

[Martin Isenburg]

Hello,

in the process of finalizing the first source code release I am
combing over the details once more. I noticed that for the scanner VLR
(= meta data that describes the hardware used) the entries may need a
bit more discussion. The last test export from RIEGL showed these
values (as reported by pulseinfo.exe):

[...]
variable length header record 1 of 13:
reserved 0
user ID 'PulseWaves_Spec'
record ID 100001
length after header 248
description 'PulseWaves 0.3 r5 (130304) by rapidlasso'
PULSEscanner 1
instrument: 'Q680'
serial: '9995495'
wave_length: 1550 [nanometer]
outgoing_pulse_width: 4 [nanoseconds]
scan_pattern: 2 ('line')
number_of_mirror_facets: 4
scan_frequency: 966.7 [hertz]
scan_angle_min: 60 [degree]
scan_angle_max: 120 [degree]
pulse_frequency: 150 [kilohertz]
beam_diameter_at_exit_aperture: 10 [millimeters]
beam_divergence: 0.5 [milliradians]
minimal_range: 0 [meters]
maximal_range: 0 [meters]
description: ''
variable length header record 2 of 13:
[...]

All looks good, except that I find the min/max scan angles so odd?
Since that was an airborne scan I was expecting them to be -30 to 30
but apparently for a RIEGL scanner the coordinate system is defined
this way (e.g. the standard exit angle of the beam is 90 degrees). So
I am thinking we probably need to enhance the specification and add
that - no matter what hardware used - the angle of the laser should be
at defined such that zero degrees corresponds to the beam pointing
down when the airborne or mobile unit is *perfectly* level. It is
supposed to tell us about the field of view but also about the case
where it points not straight down (e.g. in the pods of Airborne
Research Australia's gliders the scanner is installed at a slight
angle let's say, for example, -27 to 33 degrees.

In addition I would like to add a field that expresses how many beams
there are (on average) per scan line. Anyone opposed to this?

Martin