Death to PAPER ! More Nails in the Paper Chart Coffin . . .

[Dustymc]

Originally Posted by Jubilee39

An interesting exercise to see accuracy of charts vs actual locations is to use google earth and whatever electronic charts you wish to compare. Download actual tracks posted on any number of forums or websites and overlay them. Fiji is generally fairly accurate only a quarter mile off is some locations and spot on in others. You just have to know which is which. If you put some of the circumnavigators tracks for Vanuatu for instance Port Villa the main harbor is spot on but the track for Port resolution is a half mile inland. I have not used paper charts in years but print out critical chartlets and eyeball everything.
Joe

Datum (geodesy) - Wikipedia, the free encyclopedia

[osirissail]

Although Datums are very important and most GPS's default to WGS84 but have the capability to reselect a different Datum - - The main problem with Digital Charts seems to be in the "registering" process of converting a paper chart/acetate to a digital chart.
- - The paper chart/acetate Latitude and Longitude can be right-on or significantly different from the Lat/Lon's output by your GPS system. The older the chart the worse the discrepancy. I would suspect the cause is the inaccuracies of the original surveyor's ability to calculate Lat/Lon.

[s/v Jedi]

Originally Posted by osirissail

I would suspect the cause is the inaccuracies of the original surveyor's ability to calculate Lat/Lon.

Exactly. GPS outperforms the sextant. This means that when you use GPS navigation with it's 10 meter accuracy with a chart that was made with sextant, you get accurate coastlines / features but they are in the wrong place.

With sextant navigation this is not a problem because the navigator knows the inaccuracy of his/her position fixes and the inaccuracy of the chart might even go by undetected (it might compensate inaccuracies of the navigator).

ciao!
Nick.

[osirissail]

Simply put, in the ancient days before GPS existed, the Lat/Long on a chart was basically useful to calculate distances and to depict your approximate position (sextant or DR). When you arrived off your destination your "mark 1" eyeballs and "mark 2" brain then correlated the visual depiction on the chart of coastlines, channels, and hazards with what you were seeing outside the cockpit.
- - With GPS navigation on Chart Plotters or E-Nav computer systems something new was added - that little boat symbol on the electronic chart display which was positioned using the GPS and the underlying Lat/Long registration of the chart in use.
- - Unfortunately, there was neither time nor money for governmental chart makers to re-visit each little place depicted on their library of charts and get GPS accurate reference marks so the chart could be "re-registered." So some charts appear to be "dead on" with the little boat being where you visually discern your actual position to be. On other charts, the little boat is of varying distance from the your real world position. Especially in those situations the little boat should not be used to ascertain your actual position. Instead you revert to the "old" ways and look at the contours and hazards and their relative positions and use your eyes and brain to visually navigate safely to your destination.

[MarkJ]

Originally Posted by osirissail

- - Unfortunately, there was neither time nor money for governmental chart makers to re-visit each little place depicted on their library of charts and get GPS accurate reference marks

So private enterprise did it. Google Earth is accurate. I tried it in Tonga where the charts - all charts ecn and paper - are at least 1/4 nm out.
Google earth was SPOT ON.

Cache the Google Earth images of the areas you are going and have a GPS woring in real time on your Google Earth



Mark

[osirissail]

Google Earth may be a great planning or general familiarization aid - it does not provide depth, submerged hazards, and channel/buoy information. And add to the mix that in a lot of places Google Earth has only rather ancient low-res images where it is not possible to "zoom" in enough to see any useful information. On the other hand there are a lot of "nautical charts" that are more ancient.
- - And how are you going to utilize Google Earth while underway and no internet connection? So personally I would relegate it to a planning tool to get information about stuff that does not appear on an actual nautical chart or where the chart is blank which occurs often in the Pacific.

[MarkJ]

Originally Posted by osirissail

Google Earth may be a great planning or general familiarization aid - it does not provide depth, submerged hazards, and channel/buoy information. .

No, I use it in conjunction with other charts!
On my PC I have OpenCpn open as well as Google earth. (Plus the plotter at the helm if it decides its a nice enough day to work.)

And how are you going to utilize Google Earth while underway and no internet connection?

You don't need an internet connection to run Google Earth. Cahce the images and you can still use it.

Try it.


Mark

[osirissail]

P.S. Google Earth is a mosiac of sometimes quite ancient - out of date - photos of places you might be interested in. For instance, in St. Georges, Grenada the old GYS docks are still shown in the Lagoon even though they were destroyed more than a decade ago. Now there is a new Marina - Port Louis and the whole Lagoon is very different from what is depicted on Google Earth. This holds true in a lot of Carribbean islands where recent significant changes have been made within the last decade to harbor/bays/anchorage areas yet Google Earth is using an ancient photo that does not reflect the current situation.

[Dustymc]

I think my datum comment was a mis-reading of "the track for Port resolution is a half mile inland." If stuff is randomly off, you're probably dealing with a drunken, sextant-wielding, long-dead old-school cartographer. If stuff is systematically off, you're looking at something like datum shift.

I love how we - a bunch of stuck-in-tradition sailors - have suddenly labeled satellite imagery as "ancient," and how we're now discounting options because they don't have certain information! Are the otherwise-inaccurate paper charts more precise when it comes to things like "depth, submerged hazards, and channel/buoy information"? "Oh - this thing shows us 3 miles inland! I was wondering why that mountain had a buoy drawn on it!"

The oldest imagery used around St. Georges, Grenada in Google Earth is from Nov 4, 2003 - still before Hurricane Ivan, but still significantly less than a decade old. I suppose the paper maps have all been updated and distributed in that same timeframe?



Interestingly enough, the west side of the harbor is from 12 July 2009.

You can also get dozens of current photos of the harbor from Google Earth.



Does your paper chart do that? I just can't remember.

As I said way back in February, tools are only as good as their user. You're a fool if you try to use a tool - any tool - without knowing how it works. I see absolutely no evidence, in this thread or elsewhere, that electronic charts do not have huge benefits over paper for those willing to embrace and understand the technology.

[smurphny]

Google Earth images are nice for seeing where people are anchoring, where boats transit(if you can spot wakes), and for getting a general idea about an area but I would not trust them to plot waypoints or use with plotting software although the calibrated files APPEAR to work. As Osirissail has mentioned, there is no useful information and I have not been able to even detect buoys which would present a way to at least compare to charts.

[Dustymc]

Originally Posted by smurphny

Google Earth images are nice for seeing where people are anchoring, where boats transit(if you can spot wakes), and for getting a general idea about an area but I would not trust them to plot waypoints or use with plotting software although the calibrated files APPEAR to work. As Osirissail has mentioned, there is no useful information and I have not been able to even detect buoys which would present a way to at least compare to charts.

WTF? Are you trying to make an IFR approach to the pump station or something? The images are additional information that you can't (easily) get from other sources, and which give you knowledge that you didn't have without them. If you'd never been to a harbor, would you rather do it with outdated cartography, or with outdated cartography AND a nice image like the example I posted? Those are apparently the only choices.

[smurphny]

Originally Posted by Dustymc

WTF? Are you trying to make an IFR approach to the pump station or something? The images are additional information that you can't (easily) get from other sources, and which give you knowledge that you didn't have without them. If you'd never been to a harbor, would you rather do it with outdated cartography, or with outdated cartography AND a nice image like the example I posted? Those are apparently the only choices.

Use them to get a general idea but that's it. There ARE better sources of navigational information/charts/guides than some damned thing you hope may be somewhere near correct. Pump station? WTH are you talking about? I have saved tons of Google images and many are obviously old, some have clouds and shadows blocking the view, reflections off water and some are just plain lousy, unclear images. This tech. will get better quickly but is really of limited use right now.

[boatman61]

Originally Posted by Dustymc

WTF? Are you trying to make an IFR approach to the pump station or something? The images are additional information that you can't (easily) get from other sources, and which give you knowledge that you didn't have without them. If you'd never been to a harbor, would you rather do it with outdated cartography, or with outdated cartography AND a nice image like the example I posted? Those are apparently the only choices.

I like Potato's..... You like Potata's...
You play with your new toys and I'll stick with my Charts, Sounder and eyeballs thank you... served me well to date....
That and a good pinch of common sense...
Boats I deliver often have all the toys but they don't get switched on...
unless the owners on board and wants to play... and you can waffle all you want about things being a 1/4 mile out...
My answer... don't be clever trying to cut off corners... thats how boats hit the bottom...

[Dustymc]

Originally Posted by boatman61

I like Potato's..... You like Potata's...
You play with your new toys and I'll stick with my Charts, Sounder and eyeballs thank you... served me well to date....
That and a good pinch of common sense...
Boats I deliver often have all the toys but they don't get switched on...
unless the owners on board and wants to play... and you can waffle all you want about things being a 1/4 mile out...
My answer... don't be clever trying to cut off corners... thats how boats hit the bottom...

I hope it doesn't surprise anyone that I agree with you completely.

[Capt Phil]

Add another +, boatman61, just old fashioned, I guess. Brings to mind watching an owner trying to physically tear a Northstar chartplotter off his bridge because it put us 6 blocks inland one evening off PV before we even hit the surf line. DR on range lights and a couple of other nav aids in Banderas Bay got us in without drama. Heh Heh... Capt Phil