9. Raster Chart Material
9-5
9.2 Datum and ARCS Charts
9.2.1 Difference between ARCS chart local datum and positions in
WGS-84 datum
The difference between ARCS chart local datum and WGS-84 datum is known as WGS-84 Shift. For most of the
ARCS charts this is known and the system can do the conversion automatically. For some ARCS chart, however,
this is unknown and the operator must define the shift. For some ARCS charts this is partially known and the
operator is responsible for defining the shift for the unknown areas of partially known ARCS charts. For details, see
"How to specify operator WGS-84 shift" on page 9-9.
Further, see "Use with GPS" in the ARCS Navigator User Guide.
How the state of WGS shift is indicated permanently
No warning appears in the cursor window. The
cursor position is shown in the operator-selected
working datum. (See section 13.3 "How to Select
Datum".)
The warning "WGS undef" appears (in red) in the
Cursor window.
The system still operates in the operator-selected
working datum. However, the system is unable to
correctly do the transformation between local paper
chart datum and the operator-selected working
datum.
The warning "WGS user" appears (in red) in the
Cursor window.
The system still operates in the operator-selected
working datum. However, the system uses the
operator-defined WGS shift to perform the
transformation between local paper chart datum and
the operator selected working datum.
How to find WGS shift status of current chart
The ARCS chart legend contains a WGS shift status field. (To display the ARCS chart legend, put the cursor in the
Sidebar, confirm that the mouse functions area shows Select Sidebar, push the right mouse button, select Chart
Legend then push the scrollwheel.)
WGS shift is defined for this chart. All latitude and
longitude positions of the cursor, routes, user charts,
Notes, etc. are correctly displayed on this ARCS
chart.
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