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|  MIL-D-70789A (AR)
the DRU coordinate frame by the unit rotation matrix [R].
Elements of the rotation matrix, Ri may have the values -1, of
1. Examples are shown in Figures 28b and 28c. The relationship
between the case and DRU coordinate frames is specified by a
coordinate frame code as listed in Appendix I. There are
separate coordinate frame codes for Orientation 1 and Orientation
2.
6.6.3.2
Earth reference corrdinate frame. The earth
reference coordinate frame is an orthogonal coordinate set
points to: grid north, YE to grid east, and
downward along the local vertical. Grid north equals geodetic
north plus the grid convergence as described in TM 5-241-8,
Universal Transverse Mercator Grid, and the Ordinance Survey
When operating in the
Information Leaflet, No 72, March 1983.
extended zone, grid convergence is calculated in terms of its
present position in the extended zone, hemisphere, and reference
spheroid.
The DRU orientation
6.6.3.3 Orientation Parameters.
parameters are defined in terms of rotations between the earth
reference, intermediate, and DRU coordinate frames as shown in
Figure 29.
A set of vehicle
6.6.3.3.1 Vehicle boresight angles.
, Y, relates the DRU coordinate frame to
boresight angles,
is the horizontal
the transporting vehicle's coordinate frame.
angle between the vehicle longitudinal axis and the vertical
projection of
onto the horizontal plane when the vehicle
is measured
longitudinal axis and cross axis are level.
clockwise from the vehicle longitudinal axis direction of travel
is the vertical angle between the
and is always positive.
vertical projection of
onto the horizontal plane and Xd when
the vehicle longitudinal axis and cross axis are level.
is
negative when
lies above the horizontal plane and positive
is the angle between the horizontal plane and
when below.
measured in the Yd, Zd plane when the vehicle longitudinal axis
is positive when YD lies below the
and cross axis are level.
horizontal plane and negative when above. a may have any value
from 0 to +6399.9 mils.
may have any value from -1600 to +1600
mils
may have any value from -3199.9 to +3200.0 roils. men
the DRU is installed on a pointing device, the vehicle boresight
angles are the angles when the pointing device is stowed for
vehicle travel.
The vehicle boresight angles are nominal values because
variations may occur with prime system manufacturing tolerances,
with different weight distribution in the vehicle, with vehicle
turning and crabbing, and inexact repositioning when a pointing
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