Re: [Paddlewise] GPS & Electronic Charts

PJ Rattenbury <ratten_at_uow.edu.au> wrote:

> 	Do any PaddleWisers use electronic charts with their GPS?
>       ...<snip>...
> 	I like the principle of using satellites to accurately plot my position
> and course on to a chart. Has anyone taken this extra step?   By that I
> mean cutting the step of physically transferring latitude and longitude on
> to a chart.

You can use a GPS to immediately identify your position on a chart without
downloading charts into your GPS. The key is to create a "constellation"
of waypoints on an electronic chart (as easy as "point and click"),
print the chart with the waypoints displayed on the chart, and download
the waypoints into your GPS. The GPS "map" page will show your position
relative to this constellation of waypoints. By looking at the same
constellation on the chart, you can see right where you are. With a
sufficent density of waypoints you can identify your position on the
chart with great precision in a matter of seconds.  I have done this for
years. It works great, and is virtually "foolproof".

Note that you do not have to buy electronic charts to do this (although
that is an option). If you already have paper charts, you can scan them
into your computer, and use a program such as OziExplorer (the best!) to
convert the scanned images into charts. Alternatively, you can purchase
raster charts in BSB format (aka Maptech format in the U.S.), which
allows you to avoid the time-consuming process of scanning. These can be
purchased individually, or as sets on CD-ROMs. OziExplorer works with
scanned charts, BSB charts, DRG topos (Digital Raster Graphic
topographic maps, which are available for free on the Web for all of the
U.S.), and a variety of other map formats.  It can be used to print
charts in any scale of your choosing, with either Lat/Lon grids or UTM
grids, and of course with the waypoints that you have created by
pointing and clicking.  In then takes a single click to download the
waypoints into your GPS.

Peter also wrote:

> 	The Garmin Etrex seems to set a new standard in size, utility and water
> resistance for kayaking,  but does not appear to have capability to
> download charts.

I have owned 6 different GPS receivers, including an eTrex, and of these,
the eTrex is by far the LEAST well suited for sea kayaking (although it
is a very nice unit for hiking). The problems with the eTrex are these:

(1) When sea kayaking, one's hands are occupied with the business of
paddling. It is very inconvenient to have to stop paddling and fiddle
with the GPS receiver to access various pieces of information.  I like
being able to view critical information such as speed, heading, bearing
to a waypoint, and distance to a waypoint, while at the same time
viewing my location on the map page. All of the receivers that I have
used EXCEPT for the eTrex can display all of the above simultaneously,
without scrolling through various screens. My other receivers (depending
on the model) can display 4-9 data fields on the map page. The eTrex can
display ZERO data fields on the map page. The other display pages on the
eTrex are not much better in this regard (they can display very little
information at one time). This is not much of a problem if you are
hiking, because your hands are free to fiddle with the GPS. But it is a
major pain in the a** when you are sea kayaking. If you want to use the
map page, while at the same time viewing your speed and other
navigational information, do not get an eTrex.

(2) The location of the eTrex buttons are much less convenient than on
other GPS receivers that I have used, particularly when wearing gloves,
or when you are using the GPS in a waterproof case (which can be a good
idea, in spite of the waterproof rating). The eTrex buttons are on the
sides of the receiver. Buttons on the TOP of the receiver are much
easier to operate when wearing gloves, or when the GPS is in a case.

(3) The screen on the eTrex is very narrow, particularly in comparison
with some of the newer handheld receivers (such as the GPSmap 76). This
reduces its facility when using the map page, as you only see a
relatively thin slice of the "chart".

(4) The standard eTrex does not have differential (DGPS) capability
built in. Newer Garmin receivers (including the 76) can provide
differentially corrected (DGPS) fixes without the use of a separate DGPS
receiver/antenna. This improves the accuracy of the fix, and more
importantly the accuracy of the compass function and speed readout. Even
when zoomed into the "20-foot" setting on my newest receiver (where each
pixel is less than one foot), I see no significant drift when standing
still. DGPS really works! I do not see why anyone would buy a handheld
receiver without built in differential capability.

(5) The eTrex lacks a wide range of other useful features, including
tide tables. My newest handheld displays tide tables (and graphs) for a
wide range of primary and secondary tide stations in the U.S. and Canada.

> 	My research so far has pointed me to the Lowrance range with its new
> GlobalMap 100 GPS which is compatible with the worldwide Navionics range of
> nautical charts.  And we are talking electronic copies of actual official
> charts.  Obviously this is a more expensive route to take,  with the first
> up cost of a chart running out at US$99, but hey, if you are going to get
> into electronic gizmos..

The GlobalMap 100 is not a "new" GPS model--it was the very first
mapping handheld, and will soon be replaced. It has very limited memory
for maps, and eats through batteries at more than three times the rate
of competing receivers from Garmin. Speaking of Garmin, they are about
to release their new BlueChart nautical charts, which are compact vector
charts for use in Garmin receivers. As I explained above, however, you
do not really need to download charts into your GPS to see where you are
on your chart. I have a GPS receiver into which I can download
topographic maps, but the usefulness of this is very limited for areas
where I have created good constellations of waypoints (and printed those
waypoints onto paper charts). The resolution and readability of paper
charts will exceed that of electronic charts displayed on handheld
receivers for the foreseeable future.

Dan Hagen

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