Electronic Charts And The 972 - NorthStar 972 Quickstart Manual And Reference Manual

Electronic Charts and the 972

Getting Started
6

Electronic Charts and the 972

NOTE:
To prevent delays, it's critical that you first
obtain a Return Materials Authorization
(RMA) number from our Service
Department before returning your 972.
Shipments to BNT Marine Electronics
should be made to the following address:
One of the 972's unique features is the
ability to display both raster and vector
charts. In split screen mode, you can even
display a raster chart and a vector chart
side by side. This is a great way to under-
stand the differences and similarities
between the two.
Raster Charts
Raster charts are literally digital scans of
paper charts. In most cases, these paper
charts are issued by the local government.
The scans, like digital photos, are a matrix
of dots. The challenge in raster charts —
the earth is round (3D) and the chart is flat
(2D) — is to be able to determine the
precise latitude and longitude of each dot
at any zoom level.
One of the biggest benefits of raster charts
is their appearance – it is identical to the
Northstar Service Department
30 Sudbury Road
Acton, MA 01720
If you have special overnight or
second-day shipping requirements, please
call for turnaround time and freight costs
before you ship your 972.
paper charts. It's like having the paper
chart on the screen.
This is also one of the drawbacks to raster
charts. Since the chart is just a matrix of
dots, the chart plotter cannot tell the differ-
ence between a navaid and a depth
sounding. Furthermore, they really only
look great at one particular zoom level.
Zooming in or out from that level compro-
mises display quality.
Vector Charts
Vector charts, on the other hand, are
drawn on the screen from a set of rules
specific to each chart — instead of a digi-
tized photo of the chart, it's a
mathematical description of the chart. The
chart plotter interprets the description and
then draws (renders) the chart. Whatever
the screen resolution or zoom level, they
always look great. Rather than being a
Northstar 972