posted 09-05-2013 10:33 AM ET (US)        

--a NOAA paper chart, 14976;

--a NOAA electronic chart in raster format, essentially an electronic copy of the 14976 paper chart;

--a NOAA electronic chart in vector format;

--a Lowrance Insight electronic chart;

--a Navionics electronic chart, Great Lakes West Platinum Plus (900P+)

The NOAA electronic charts are available on my laptop computer, which I was not carrying on this trip, so they were not available to me as I was navigating up there. I am including them for reference in this discussion. The Lowrance and Navionics electronic charts were available on my HDS-8 chart plotter. And, of course, the paper chart was available, if I wanted to unroll it. Most of the time while underway the paper chart was not available at the helm. For much of the trip, I used the Navionics electronic chart on the HDS-8 as the primary source of chart data.

When approaching the entrance to McCargoe Cove from the North, I could easily see two large rocks offshore about a half mile, known as Ollies Dogs Rocks. However, these rocks were not shown on the Navionics chart. Only a shoal area was indicated in the region of the rocks. Below are four views of this area on four different charts:

Ollies Dogs Rocks

Navionics

Lowrance INSIGHT

NOAA Raster

NOAA Vector

The Navionics chart is quite different than the other three. It fails to show the rocks above the surface of the water. These are large rocks, easily seen, and extend at least six feet above the surface of Lake Superior. It was quite disturbing to discover they were not very clearly indicated on the Navionics chart.

The Lowrance chart does a better job of presenting the hazard. The chart clearly shows two rocks above the water surface. The NOAA charts show them, too.

posted 09-05-2013 01:51 PM ET (US)            

I most often use the NOAA Booklet Charts, as they are far less cumbersome to use on an open boat than the full chart version. While orienting yourself to the proper page can be a challenge, once there, you seldom need to turn pages due to the scale of the documents. Prior to departing on a trip, I'll print and spiral bind the Booklets into a single 8 1/2 x 11 document with an acetate cover and drop it in the console.

Here is NOAA Chart 14976 in Booklet format:

posted 09-05-2013 05:28 PM ET (US)            

Crystal Cove

Navionics. Note that again the hazard (the rock) is not shown, only a shoal area.

Lowrance Insight. The rocks are shown, but they are drawn as if on land.

NOAA Raster. Shoal and rocks are indicated.

posted 09-05-2013 05:43 PM ET (US)            

Southwest Isle Royale, Washington Harbor

Navionics. The rock is shown as a small islet.

Lowrance Insight. The rock and shoal are completely omitted. It would be very dangerous to navigate with this chart in this area at any time when visibility was reduced or at night.

NOAA Raster.

posted 09-05-2013 09:07 PM ET (US)            

FYI, here are the Garmin BlueChart G2 maps (HCA015R) for the sames areas:

Ollies Dogs Rocks: http://www.myfishingpictures.com/data/500/Ollies_Dogs_Rocks.png

Crystal Cove: http://www.myfishingpictures.com/data/500/Crystal_Cove.png

Washington Harbor: http://www.myfishingpictures.com/data/500/Washington_Harbor.png

posted 09-06-2013 08:15 AM ET (US)            

Stop the presses!

I just discovered that the Navionics chart presentation was being affected by my user settings. I had customized the presentation to turn off a lot of features, like "show international boundaries", or "show light sectors," and many others. It turns out that in the menu structure for customizing presentation, representation of hazards like rocks is part of the "Other elements" group. I had this turned off.

One would not think that presenting serious hazards like rocks awash would be a feature that could be turned off, and, even stranger, that this feature would be listed under "Other elements" in the menu structure. However, that appears to be the case. With the Navionics charts set to "Show All", the rock hazards are clearly shown. Here are two new screenshots, showing the Navionics presentation for Crystal Cove and Ollies Dogs Rocks:

Navionics Chart; All Features ON; Crystal Cove

Navionics Chart; All Features ON; Ollies Dogs Rocks

This is a much better presentation. I always say, "I learn something every time I go boating." I certainly learned something in this thread--don't turn off "Other elements" in your Navionics chart presentation options.

posted 09-06-2013 10:03 AM ET (US)            

On a Humminbird chart plotter that I had, the "live" or active track was fine, recording a point every second, but the default setting for the saved track, probably to save memory, was 10 seconds, meaning it record only one out of every 10 actual points.

As a result, the circumvention of a tip could appear fine live but, when reviewing it on the saved track, it would seem like you ran over ground.

posted 09-07-2013 09:40 PM ET (US)            

quote:

---

saumon, Is that the Garmin G2 Vision or the G2 maps?

---

Those screenshots are from the regular G2 map (non-Vision). Having both, I find out that the only added feature of the Vision maps are the 3D view but, on the other hand, the regular G2 maps have a lot more depth soundings and contour lines.

posted 09-07-2013 11:58 PM ET (US)            

http://www8.garmin.com/support/collection.jsp?product=010-00527-00

As an example, that same map (G2 non-Vision HCA015R) didn't show that much details when viewed with the older MapSource software on my computer while the newer HomePort software show all the detailed contour lines...

posted 09-08-2013 01:15 AM ET (US)            

by looking at the change history log ( http://www8.garmin.com/support/ch.jsp?product=010-00527-00 ), it seems they added the support for the BlueChart G2 version 11.5 and later when releasing the 3.80 software version. If your software is up-to-date and still not showing much details, it could simply be that you have an older version of the chart.

posted 09-08-2013 07:27 AM ET (US)            

The track recording rate was high enough to correctly show the course. (The setting for track recording rate was "AUTO", which records a track point whenever the boat heading changes.) I am comfortable with the recorded track position as being accurate.

In the area of Southwest Isle Royale, as we entered into Washington Harbor, the track of my position plotted on the various electronic charts shows the boat crossing over land. I sent the track to Saumon in GPX format, he imported the track into his computer charting application, Garmin Homeport, and he emailed me a screen shot showing the GPS receiver position track on the Garmin charts for that area. The result is seen below:

Garmin Chart with vessel track

As you can see, the plot of my track on the Garmin chart also takes us over land. This seems to agree with all the other charts, leading to two possible explanations:

--the general position of land features in the Isle Royale area is drawn incorrectly on all the charts, or

--the position fix from my GPS receiver is in error

Based on my experience with the GPS receiver position fix and other charts in other locations, the deduced position has been very accurate. For areas with high resolution charts, for example, a marina with individual boat slips shown, the GPS receiver position fix usually is so accurate the boat is shown precisely located, even to the position relative to finger docks and slips.

I suspect that all the electronic charts have been developed from the same base, the NOAA paper chart cartography. If that data has a slight offset in position of the land masses, it would be reasonable that this error might show up in all the electronic charts. This would explain why all the electronic charts seem to show the same error with regard to the vessel track in the SW Isle Royale area shown in the above screen captures.

posted 09-08-2013 06:54 PM ET (US)            

Is the error seen in the GPS track as plotted on six different electronic charts due to:

--an error in the position deduced by my GPS receiver at that particular time and place, or,

--and error in the charted position of the land on all six charts which are likely all taken from the same survey.

I have already expressed my opinion, but let me repeat it for clarity:

The error is due to an error in the charted position of the land which is reflected in all six charts because all of them are based on the same (old) survey.

If someone has the opposing position, that is, that the error is due to my GPS receiver failing to deduce the correct position, please let me know, and please make it clear. I don't understand how I am supposed to make an inference from reading some article on another website about this question.

posted 09-09-2013 04:51 PM ET (US)            

LINK to large image
Track of my boat Washington Harbor at the small boat dock.

Next, here is the track plotted on the map for the passage through Thompson Island and near the wreck of the AMERICA. The plot over YahooMaps shows the boat track correctly. The boat did not travel over land.

LINK to large image
Track of my boat passing close to Thompson Island

In plotting the track on a map that is independent of the NOAA maps, Steve has shown:

--the GPS receiver was accurately tracking the position

--the maps developed from an independent source, not from NOAA, show the track precisely as it was actually run.

Based on this evidence from Steve, it is clear that the error seen with the NOAA charts, all five electronic versions, is a result of an error in the location of the land on those charts, and not from an error in the GPS receiver. When the GPS derived track is plotted against a satellite derived map, the accuracy of the track is excellent.

posted 09-09-2013 05:02 PM ET (US)            

Near the wreck America and passing Thomson Island, the track fits perfectly with the details shown in this satellite view.

posted 09-09-2013 07:45 PM ET (US)            

My Garmin 78 is using US ALL & Canadian West Coast g2 HXUS039R
FEB 2013 010-c1018-20

The 3206 uses its internal g2 charts and I also have the G2 RUS040R US East G2 Feb 2012 010-C1014-10 map on a Data Card.

All three of these maps cover Isle Royal, but none of them give me the same detail on home port or on either unit as the detail you are showing in your screen shots. The 3206 and 78 are updated.

posted 09-11-2013 01:54 PM ET (US)            

It should be realized that Isle Royale is a rather remote island. Its closest approach to Michigan is about 56-miles. Its closest approach to Minnesota is about 14-miles. These long distances over water may have limited the precision of any land survey done prior to the now common use of GPS-receiver measurements. An error of 100-feet in the charted position of the island is reasonable, and seems to be apparent in the electronic chart cartography developed from the NOAA sources.

posted 09-11-2013 03:58 PM ET (US)            

When you enter "Isle Royale" in the search box, it return 416 results and you can preview the maps. Those from the 70's, 60's and 50's didn't include their land contour sources but the same identical maps fron the 40's indicate that the land contours were taken from a 1908 Michigan Geological survey.

The map published in 1909 list the persons who made the survey, from 1867-1871, and resurveyed certains parts (like the Western portion) in 1905-1906.

posted 02-11-2014 10:16 PM ET (US)            

Actually, GPS doesn't work all that well in the far northern
and southern latitudes because the satellites don't get that
far north and south. The Russian GLONASS satellites are in
a more steeply inclined orbit that does cover those areas
better. That's understandable given that the Russians have
a great deal of land mass up there.

posted 02-13-2014 09:20 AM ET (US)            

The satellites in the NAVSTAR GPS are in orbits with a 55-degree inclination. This suggests that the highest latitude which a NAVSTAR GPS satellite will reach in terms of its ground position on the Earth is going to be 55-degrees latitude. The satellites in GLONASS are in orbits with 64.8-degree inclination, which suggest the GLONASS satellites will pass overhead at some points on the earth at latitude 64.8-degree.

I can't find any reasonably authoritative resource that confirms Chuck's statement that "GPS doesn't work all that well in the far northern
and southern latitudes." It certainly works. I suppose the question is one of a comparative, that is, how well does it work?

What I can find is some mention that a position fix solution obtained with GLONASS could have a better (lower) dilution of precision compared to the NAVSTAR GPS, due to the orbit inclination of the GLONASS satellites.

quote:

---

Users in higher latitude areas, such as Canada, obtain better GLONASS derived dilution of precision (DOP) than users of GPS. This is due to the high inclination angle of GLONASS: 64.8 degrees compared to 55 degrees for GPS.

---

Cf.: http://www.ifp.uni-stuttgart.de/publications/phowo07/220Eissfeller.pdf

However, I think the distinction is moot for us as boaters because in the higher latitudes--very high, say above 70-degrees--there is not much recreational boating occurring. For recreational boating use, the NAVSTAR GPS does not suffer any particularly inferior performance relative to GLONASS. at least not at any latitude in which any of us are likely to be boating.

posted 02-15-2014 06:35 PM ET (US)            

http://earthnc.com/chartviewer/index.php?ll=48.11405309279205,-88.69195342590332&z=15

posted 02-15-2014 07:19 PM ET (US)            

MMM, when I get a chance I'll have a look at my electronics
topo sheets and see what they say.

Chuck?

posted 02-16-2014 07:57 PM ET (US)            

By way of comparison, in Monterey, CA, NAD27 CONUS lattitude
is 0.004 minutes greater than WGS84, and latitude is 0.061
minutes less than WGS84.

Still not bad given they surveyed NAD27 CONUS starting
somewhere in the midwest using a transit, tape, and thermometer.

JimH: Just for grins can you e-mail me your Washington Harbor
track? [Sent--jimh]

posted 02-17-2014 08:35 PM ET (US)            

I guess the USGS (does topo sheets) got it righter than NOAA
(does nautical charts).

posted 02-19-2014 09:28 PM ET (US)            

To follow up on my question--go back many posts in the thread to find it--of what is in error, the position deduced by my GPS receiver with a very low HDOP and with WAAS augmentation of precision, or the several electronic charts, all derived from NOAA surveys, it seems crystal clear to me that the chart data is off and the GPS receiver fix is fine.