| Version 58 (modified by wja, 2 years ago) (diff) |
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Lever arm offset details
This page gives details of the lever arms used when processing data collected from the sensors.
Surveys are undertaken by an external company, usually once a year.
Where possible, the lever arms use precise prime points, e.g. the phase centre of the master (rear) antenna, the centre of the IMU, the scan mirror centre for the LiDAR and the focus point of the lens for the Eagle, Hawk and CASI.
Since 2011, nav data is transformed from the IMU/GPS to an imaginary reference point below the plane (the PAV80). The relevant sensor processing software will then transform from this point to the correct sensor.
Info about calculating the lever arms.
2022
This year had two flight configurations:
1) Owl attached to IPAS20 IMU, PhaseOne 2) Optech LiDAR, IBIS, PhaseOne
Units are the following:
- X: Positive towards starboard (right)
- Y: Positive towards the nose
- Z: Positive towards the sky
Owl
These measurements have been derived from the following:
- Aircraft survey (note this is not the usual twin otter!): /users/rsg/arsf/arsf_data/2022/misc/aircraft_survey_VP-FBL/twin_otter.dwg. Viewed with LibreCAD.
- Owl schematics: /users/rsg/arsf/doc/schematics/owl/
X
Back left corner offset from antennae was measured from survey. Offset to Owl pupil measured from schematic.
-0.3970 - 0.1415 = -0.5385
Y
The same back left corner offset used from survey. Offset to pupil from schematic.
0.799 - 0.09565 = 0.70335
Z
Base of sensor offset from anntennae was measured from survey. Offset from this to the pupil was measured from the schematic.
-1.541 + 0.1613 = -1.3797
IPAS20 IMU
This IMU is only to be used for processing Owl data. It was attached to the Owl, which was on a fixure allowing the viewing angle to me moved.
Unfortunatly, we do not have information regarding the inside reference location of this IMU. The survey has been used to find the coordinates of the center of the top face of the instrument, and then half the length was offset for the Z offset. As per done previously, see /users/rsg/arsf/arsf_data/2012/misc/dornier_survey/workings_out.txt.
These values are for the lengths from the antennae to the IMU, but for input into IPAS TC, these are reversed so that they are the distance from the IMU to the antennae.
X
-0.2415 - (0.093 / 2) = -0.288
Y
0.5915 + (0.093 / 2) = 0.638
Z
-1.368 - ((-1.368 - -1.468) / 2) = -1.418
IBIS
Callum Middleton measured from the antennae to the back right corner of the IBIS. See image /users/rsg/arsf/arsf_data/2022/misc/leverarms/ibis_ref_point.jpg for the location of this corner.
Using the schematic, the offset to the IBIS pupil has been calculated.
X
The 161 value on the schematic has been rounded down to 160 (0.16 below) to account for the 'cutaway' edge where the reference point was measured. We don't have the exact measurement for this axis otherwise.
-0.583 - (0.160 / 2) = -1.383
Y
-0.814 - (0.230 - 0.075) = -0.969
Z
(-1.014 - (0.498 + 0.09)) + 0.062 = -1.54
2015
The Twin Otter was surveyed in July 2015. Do not use these values for data collected from the Dornier. At the time of the survey the RCD was broken, so there are no RCD lever arms calculated.
Unless otherwise stated, values are X positive to nose, Y positive to starboard, Z positive down.
IPAS
These values should be entered into IPAS if you are processing the nav for hyperspectral or lidar. They are lever arms from the PAV80 (an imaginary point below the LiDAR instrument) to the device stated:
| X | Y | Z | |
| GNSS (antenna) | 4.3533 | 0.4201 | -0.2555 |
| IMU (honeywell) | -0.409 | 0.207 | -0.174 |
| IMU (litton) | -1.7292 | 0.1513 | -0.1645 |
The IPAS honeywell is linked with the LiDAR. The IPAS20 (litton) is external and should be used for Fenix processing.
If using the litton IMU the IMU boresight angles also need to be edited and set to 0, 0, 0.
APL
These values go in the file leverarm_values.csv. They are from the PAV80 to the relevant sensor:
| X | Y | Z | |
| Fenix lens | -1.7407 | -0.0139 | 1.2605 |
| OWL principal point | -0.0685 | 0.5201 | 0.35725 |
2014
Aircraft was surveyed by Sterling Surveys in August 2014
Unless otherwise stated, values are X positive to nose, Y positive to starboard, Z positive down.
IPAS
These values should be entered into IPAS if you are processing the nav for hyperspectral or lidar. They are lever arms from the PAV80 (an imaginary point below the LiDAR instrument) to the device stated:
| X | Y | Z | |
| GNSS (antenna) | -0.128 | -0.008 | -1.674 |
| IMU (honeywell) | -0.409 | 0.207 | -0.174 |
RCD
If you are processing the nav for the RCD, use the following values. They are lever arms from the RCD to the devices stated:
| X | Y | Z | |
| GNSS (antenna) | -0.257 | -0.066 | -1.675 |
| IMU (honeywell) | -0.538 | 0.149 | -0.175 |
If you're using the external IMU (litton, sometimes called IPAS20):
| X | Y | Z | |
| IMU (litton) | 0.485 | 0.145 | -0.187 |
APL
These values go in the file leverarm_values.csv. They are from the PAV80 to the relevant sensor:
| X | Y | Z | |
| Fenix lens | 0.477 | -0.024 | -0.208 |
| OWL principal point | 0.881 | 0.010 | -0.226 |
Aircraft was surveyed by Sterling Surveys in March 2014
Unless otherwise stated, values are X positive to nose, Y positive to starboard, Z positive down.
IPAS
These values should be entered into IPAS if you are processing the nav for hyperspectral or lidar. They are lever arms from the PAV80 (an imaginary point below the LiDAR instrument) to the device stated:
| X | Y | Z | |
| GNSS (antenna) | -0.132 | -0.014 | -1.675 |
| IMU (honeywell) | -0.409 | 0.208 | -0.174 |
RCD
If you are processing the nav for the RCD, use the following values. They are lever arms from the RCD to the devices stated:
| X | Y | Z | |
| GNSS (antenna) | -0.261 | -0.077 | -1.680 |
| IMU (honeywell) | -0.538 | 0.144 | -0.179 |
If you're using the external IMU (litton, sometimes called IPAS20):
| X | Y | Z | |
| IMU (litton) | 0.515 | 0.15 | -0.186 |
APL
These values go in the file leverarm_values.csv. They are from the PAV80 to the Fenix:
| X | Y | Z | |
| Fenix lens | 0.504 | -0.018 | -0.201 |
2013
Aircraft was surveyed by Sterling Surveys in April 2013
Unless otherwise stated, these values have the PAV80 as the origin and are X positive to nose, Y positive to starboard, Z positive down.
These values are not adjusted for the phase centre of the antenna.
LiDAR
LiDAR lever arm values.
These values should be entered into IPAS:
| X | Y | Z | |
| GNSS (antenna) | -0.128 | -0.028 | -1.679 |
| IMU (honeywell) | -0.409 | 0.207 | -0.174 |
Hyperspectral
Eagle and Hawk lever values. These values go in the file leverarm_values.csv:
| X | Y | Z | |
| Eagle (lens) | 0.39 | -0.009 | -0.198 |
| Hawk (lens) | 0.587 | 0.006 | -0.147 |
RCD
These values have the RCD lens as the origin. They should be entered into IPAS when creating a camera sol file.
| X | Y | Z | |
| GNSS (antenna) | -0.260 | -0.088 | -1.678 |
| IMU (honeywell) | -0.541 | 0.147 | -0.173 |
IPAS 20 (Litton)
If using the IPAS20 (Litton) the following IMU values should be entered into the IPAS software.
Note that the IMU Litton was not in the aircraft at the time of the 2013 survey, values for the GPS to IMU litton from 2012 were used to calculate the values below.
| X | Y | Z | |
| LiDAR IMU (Litton) | 0.393 | 0.157 | -0.166 |
| RCD IMU (Litton) | 0.261 | 0.097 | -0.165 |
2012
Aircraft was surveyed by Sterling Surveys in July 2012
Full report, images and various workings out are at ~arsf/arsf_data/2012/misc/dornier_survey/
Unless otherwise stated, these values have the PAV80 as the origin and are X positive to nose, Y positive to starboard, Z positive down.
These values are not adjusted for the phase centre of the antenna.
LiDAR
LiDAR lever arm values.
These values should be entered into IPAS:
| X | Y | Z | |
| GNSS (antenna) | -0.127 | -0.012 | -1.677 |
| IMU (honeywell) | -0.409 | 0.207 | -0.174 |
These values go into ALSPP (I think):
| X | Y | Z | |
| Lidar (mirror centre) | -0.140 | 0.000 | -0.170 |
Hyperspectral
Eagle and Hawk lever values. These values go in the file leverarm_values.csv:
| X | Y | Z | |
| Eagle (lens) | 0.394 | -0.02 | -0.143 |
| Hawk (lens) | 0.581 | -0.019 | -0.131 |
RCD
These values have the RCD lens as the origin. They should be entered into IPAS when creating a camera sol file.
| X | Y | Z | |
| GNSS (antenna) | -0.258 | -0.074 | -1.678 |
| IMU (honeywell) | -0.540 | 0.145 | -0.175 |
2011
Aircraft was surveyed by Sterling Surveys in March 2011.
LiDAR
The LiDAR measurements are made from the antenna to a reference point, then transformed from that reference point to an internal point (PAV 80). The reference point is the front left corner of the LIDAR sensor unit casing.
Measured antenna to reference point numbers:
- X = 0.173 ; Y = 0.073 ; Z = -1.412
LiDAR lever arm values (and the values to enter into the software):
| X | Y | Z | |
| GNSS | -0.144 | -0.029 | -1.672 |
| IMU | -0.411 | 0.206 | -0.192 |
| User Frame | -0.142 | -0.001 | -0.188 |
These values are entered in the flight planning software and should automatically populate in IPAS.
Hyperspectral sensors
The hyperspectral measurements are made from the antenna to a reference point, then transformed from that reference point to the Eagle/Hawk lens. The reference point is the forward port corner of the Eagle/Hawk base plate.
Measured antenna to reference point numbers:
- X = 0.864 ; Y = 0.300 ; Z = 1.569
Eagle and Hawk lever arm values are:
| X | Y | Z | |
| Eagle | 0.559 | -0.015 | -1.543 |
| Hawk | 0.729 | -0.015 | -1.543 |
RCD
For processing the sol file for the RCD use the following lever arm values:
| X | Y | Z | |
| GNSS | -0.256 | -0.090 | -1.612 |
| IMU | -0.523 | 0.145 | -0.132 |
2010
Where unspecified, the measurements are as in the previous year.
LIDAR
Internal measurements provided by Leica:
- PAV80 rotation point to RCD lens (no spacer): X= 0.112 ; Y = 0.061 ; Z = -0.060
Axes are:
- X = increasing towards the front of the plane
- Y = increasing to port
- Z = increasing downwards
Note that to get to PAV80 from reference point we apply: X = -0.14 ; Y = 0 ; Z = -0.17 (see email March 2010 from Leica)
Lever arm values to enter into the IPAS software for 2010:
| X | Y | Z | |
| GNSS | 0.019 | -0.024 | -1.692 |
| IMU | -0.411 | 0.206 | -0.192 |
| User Frame | -0.142 | -0.001 | -0.188 |
These values are entered in the flight planning software and should automatically populate in IPAS.
Hyperspectral sensors
We're told these are the same as end of 2008. Note: These are xyz co-ords, not gam-del-dst
| X | Y | Z | |
| Eagle | 0.408 | 0.001 | -1.548 |
| Hawk | 0.578 | 0.001 | -1.548 |
2009
Hyperspectral sensors
We're told these are the same as end of 2008. Note: These are xyz co-ords, not gam-del-dst
| X | Y | Z | |
| Eagle | 0.408 | 0.001 | -1.548 |
| Hawk | 0.578 | 0.001 | -1.548 |
TABI
Measured by ARSF-Ops relative to Hawk (numbers converted below to relative to the GPS antenna), not surveyed. Should be accurate enough though.
| X | Y | Z |
| 0.858 | 0.001 | -1.548 |
Applanix IMU
Use 2006/7 numbers?
Leica LIDAR + IMU
The LIDAR survey measurements are made from the antenna to a reference point, then transformed from that reference point to internal points (the IMU and mirror center). The reference point is the front left corner of the LIDAR sensor unit casing. Survey was in late 2008.
Measured antenna to reference point numbers:
- X = 0.010 ; Y = 0.078 ; Z = -1.432
Internal measurements provided by Leica:
- reference point to mirror center: X = 0.169 ; Y = 0.102 ; Z = 0.090
- reference point to IMU: X = -0.269 ; Y = 0.207 ; Z = -0.004
- laser mirror centre to RCD lens (no spacer): X= 0.239 ; Y = 0.062 ; Z = -0.060
Axes are:
- X = increasing towards the front of the plane
- Y = increasing to port
- Z = increasing upwards
2008
18th Dec. 2008: Due to confusion about angle directions, the originally computed gamma angles are incorrect. The error caused should be of similar magnitude to the previous, similar error (ie ~1.5m along-track for ATM, other sensors will have a smaller error). Because the error will be partially compensated for by boresight angles depending on flight altitude, the "wrong" numbers should be used anyway unless you re-calculate the boresight angles.
Jan 2008 numbers (Wrong but use anyway, or we have to redo boresights):
| Gam | Del | Dst | |
| ATM | 1.2258 | 0.0051 | 1.7380 |
| Eagle | 1.0748 | -0.0036 | 1.7441 |
| Hawk | 0.9705 | -0.0049 | 1.7985 |
Jan 2008 numbers (Corrected for reference but use "wrong" numbers above, unless you've redone boresights):
| Gam | Del | Dst | |
| ATM | 0.3450 | 0.0051 | 1.7380 |
| Eagle | 0.4960 | -0.0036 | 1.7441 |
| Hawk | 0.6003 | -0.0049 | 1.7985 |
VOCALS
Use these numbers for VOCALS flights from autumn 2008. Note: These are xyz co-ords, not gam-del-dst (ie use -acx, not -acv)
| X | Y | Z | |
| Eagle | 0.2302 | 0.001 | -1.548 |
| Hawk | 0.4002 | 0.001 | -1.548 |
Applanix IMU
Use 2006/7 numbers?
Leica LIDAR + IMU
The LIDAR survey measurements are made from the antenna to a reference point, then transformed from that reference point to internal points (the IMU and mirror center). The reference point is the front left corner of the LIDAR sensor unit casing. Survey was in late 2008.
Measured antenna to reference point numbers:
- X = 0.010 ; Y = 0.078 ; Z = -1.522
Internal measurements provided by Leica:
- reference point to mirror center: X = 0.169 ; Y = 0.102 ; Z = 0.090
- reference point to IMU: X = -0.269 ; Y = 0.207 ; Z = -0.004
Axes are:
- X = increasing towards the front of the plane
- Y = increasing to port
- Z = increasing upwards
The GNSS lever arms to enter into the IPAS software are (i think): X = 0.159 Y = -0.024 Z = -1.522
The IMU lever arms to enter into the IPAS software are: X = -0.269 Y = 0.207 Z = -0.004
2007
Use 2006 numbers..
2006
Obs and results as follows:
v:200601 may 2006
2006 D-CALM instrument coords from SJR 9th May
------------------------------------------------------------------------------------------
z x y Z offset X offset Y offset dst gam del
ATM 8.991 96.9065 99.9881 -1.68 0.4565 -0.0029 1.741 0.2655 0.006353
CASI 9.156 97.22509 99.98485 -1.515 0.775092 -0.00615 1.702 0.4732 0.007934
Eagle 9.143 97.7307 99.99 -1.528 1.2807 -0.001 1.994 0.6977 0.000781
Hawk 9.143 97.9155 99.99 -1.528 1.4655 -0.001 2.117 0.7644 0.000682
IMU 9.182 97.5181 99.8089 -1.489 1.0681 -0.1821 1.841 0.6287 0.1689
560 -1.476 1.4831 -0.0061 2.092 0.8264 0.004113
Pant 10.945 100.001 95.095 0.274 3.551 -4.815
Sant 10.906 100.000 104.91 0.235 3.550 5.000
Fant 10.843 101.661 99.989 0.172 5.211 0.079
------------------------------------------------------------------------------------------
Aant 10.671 96.450 99.991 0.0 0.0 0.0
------------------------------------------------------------------------------------------
Axes: Y+ port, X+ tail to nose, Z+ up
Antennas: name, postion, AT4 name, survey name
Aant = aft = master = GPS4
Fant = fore = slave_1 = GPS3
Pant = port = slave_2 = GPS1
Sant = starboard = slave_3 = GPS2
--------------
Sensor offset vector paras allowing for this coordinate system
dx == X offset, dy = Y offset, dz = Z offset
dst = sqrt( dx * dx + dy + dy + dz + dz )
gam = acos( abs(dz) / dst )
del = atan( dy / (-dx) )
Units: dst: metres, gam, del: radians
-----------------
Verification test
p = r = h = 0
ant1: lat: 52.0 lng: -3 hgt: 1000
IMU is at: lat: 52.00000959 lng: -2.99999734 hgt: 998.511013
==========================================================================================
Applanix IMU Lever arm offsets
| Year | X | Y | Z |
| 2006 | 1.068 | 0.182 | 1.489 |
| 2007 | Use 2006 :S | Use 2006 :S | Use 2006 :S |
N.B. Some of the 2006, 2007 data has a preset IMU lever arm offset of 0.907, 0.190, 1.783 - not sure where this comes from, perhaps coords noted on the plane? Dave Davis has said to use the 1.068, 0.182, 1.489 offsets.