Motion Modes; True Motion - Sperry Marine Visionmaster FT ECDIS User Manual

Basic Operation of ECDIS ECDIS User Guide

Motion Modes

The motion mode determines how the trails of moving targets are shown
across the screen relative to own ship and how chart information is
updated.
The only motion mode available to ECDIS is True Motion
(TM). The motion mode is displayed as an abbreviation
at the top right of the screen.

True Motion

In TM, own ship moves across the screen by the system applying Latitude
and Longitude (L/L) positional updates to it. All stationary items (i.e. items
with constant L/L coordinates) remain in a fixed position on the screen and
all targets move according to their true course and speed.
When own ship reaches the edge of the TM limits box, and true motion
reset limits are enabled, it is repositioned to the edge of the box, such that
a line drawn from own ship's CCRP in the direction of the current course
passes through the centre of the TM Limits box (see figure below).
The TM limits box default size is approximately 90% of the chart window
size (90% being the maximum size of the box). The box size can be
redrawn by the operator, see Setting True Motion Limits.
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