Chapter 11 - Setting up your 957
957 Operator’s Manual, Rev. B Page 139
Choosing rhumb
line or great circle
calculations
You can set the 957 to calculate the distance and initial
bearing to your intended destination along either a great circle
route or a rhumb line.
The shortest distance between any two points on the surface
of a sphere is called a great circle route. It appears as a curved
line on a Mercator chart.
Rhumb line navigation maintains a constant true direction to
your destination (seen as a straight line on a Mercator chart),
but is a somewhat longer route to travel over great distances
than the great circle calculation. Rhumb line is the 957’s
default method of calculating distance and bearing to
waypoints.
Great circle and rhumb line are virtually the same if the start
and end points are closer than 100 nm. You can approximate a
great circle using a series of shorter rhumb lines.
Choosing distance
and speed units
You can set the 957’s display of distances and speeds to any of
the following units of measurement:
•
nautical miles and knots (nm/knots)
•
kilometers and kilometers per hour (km/kph)
•
statute miles and miles per hour (mi/mph)
This option also sets whether cross-track and
distance-to-waypoint information on the STEERING and 3-D
STEER screens is displayed in feet or meters (the km/kph
setting will display meters).
CAUTION!
Regardless of your selection, your cross-track error (including
the steering indicator and autopilot output) is always calculated
from a rhumb line, and the route lines on the chart are rhumb
lines.
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