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ECDIS-E User Guide Charts
65934012 4-33
The Polar Stereographic projection can be used to display any region of the
earth, including the north and south poles (up to 90 degrees north or
south).
The Chart Projection menu allows the operator to specify which of the two
projection types they prefer to use for display. The preferred projection is
local to each node and is persisted.
On ECDIS the Chart Projections window includes a Primary and Secondary
Chart Display. The primary and secondary chart displays may use different
Active Projections at the same time.
Whenever the displayed region changes (due to scale change, panning,
TM reset or Goto) the system attempts to the use the preferred projection
to render the chart and all other synthetics. If preferred projection is
unavailable in the displayed region, then the system will select an `Active
Projection' from the available projections that are supported by the current
chart engine.
For example, if the preferred location is Mercator but the chart is displaying
a high latitude region the Active Projection will automatically change to
Polar Stereographic to render the chart display.
SevenCs vector based charts are displayed in all chart projections,
whereas CMAP is only displayed in Mercator projection. At high latitude
regions, using Polar Stereographic projection, C-MAP charts are
suppressed and a permanent prompt
Chart Suppressed at High Latitude
appears. CMAP charts are restored when the chart enters a geographic
region where Mercator is allowed.
When an ARCS chart is displayed the chart will
dictate the projection for that display. As a result,
the Active Projection value will always be ARCS
when an ARCS chart is displayed, regardless of
what is the preferred projection.