The Electronic Charting "Zoom Problem"

[transmitterdan]

Not many dedicated chart plotters have raster chart capability these days. There is no information about depth and other contextual information in a raster chart that a computer can decipher. Many countries have stopped issuing raster charts.

The counter to that is raster charts can be "self manufactured" using Google Earth or some other satellite imagery database. These are very useful in a lot of situations. I hope OpenCPN will always support this.

[Dockhead]

Originally Posted by transmitterdan

Dockhead,

It is only 2.5 nautical miles longer than a straight rhumb line track. That's not too bad (10% longer) and barely 30 minutes travel time for a boat like yours I would think. I presumed this is a motor sail (heavy on the motor) and 30 minutes is a small price to pay for some peace of mind.

The process on OpenCPN is quite easy. Here is an outline of what I did:

1) Make a rhumb line route for reference.
2) Start a new route working from both ends finding the obvious way in/out of the end points.
3) Then trying to stay as close to the rhumb line but taking the shortest "recommended track" paths connect the start and finish.
4) Once I have both start and finish connected then zoom out and see how it looks.
5) Then pan along the route moving points and adding points close to hazards.

If I were really going to make this trip I would put names on the waypoints that warn of hazards to port or starboard so when the autopilot is making for that point it will tell me there is a hazard to P or S.

The whole process took about 45 minutes.

Then I sent the route over to google earth and flew it looking for obstructions. Didn't see any. There is a tricky passage that I might decide to go around. So here again I would create a route around that area and when I got there decide which way to go either using the shortest route or the go-around depending on my confidence and conditions.

I am fairly confident that I could not do this on paper in the same time and with the same degree of precision and detail. What do I win?

Interesting that you think it wouldn't have been easier in paper. I did it exactly the way you did, but it would have taken me half the time in paper! But let's keep in mind that this is not on a plotter, but on OpenCPN, which is among electronic means the first among equals . . .

What do you win? Why, the Dockhead Skillful Navigator Prize, of course! Redeemable in as much gin as you can drink on board on a beautiful Baltic evening this summer!

[sailorF54]

Originally Posted by transmitterdan

Dockhead,

It is only 2.5 nautical miles longer than a straight rhumb line track. That's not too bad (10% longer) and barely 30 minutes travel time for a boat like yours I would think. I presumed this is a motor sail (heavy on the motor) and 30 minutes is a small price to pay for some peace of mind.

The process on OpenCPN is quite easy. Here is an outline of what I did:

1) Make a rhumb line route for reference.
2) Start a new route working from both ends finding the obvious way in/out of the end points.
3) Then trying to stay as close to the rhumb line but taking the shortest "recommended track" paths connect the start and finish.
4) Once I have both start and finish connected then zoom out and see how it looks.
5) Then pan along the route moving points and adding points close to hazards.

If I were really going to make this trip I would put names on the waypoints that warn of hazards to port or starboard so when the autopilot is making for that point it will tell me there is a hazard to P or S.

The whole process took about 45 minutes.

Then I sent the route over to google earth and flew it looking for obstructions. Didn't see any. There is a tricky passage that I might decide to go around. So here again I would create a route around that area and when I got there decide which way to go either using the shortest route or the go-around depending on my confidence and conditions.

I am fairly confident that I could not do this on paper in the same time and with the same degree of precision and detail. What do I win?

I do agree with what is said above. There is one nice feature that I think has not been mentioned. On vector charts (such as CM93) you can set a safety level (I chose 5 m depth) and I had everything shallower painted light blue (between 3 and 5 meters) and darker blue (between 0 and 3 m), using the shallow and deep settings. Now the game is to avoid (wherever possible) the blue patches, follow recommanded routes and stay as close as possible to the rumb line I had also traced on the chart.

Here's my route (done in less than 10', not checked with Google Earth)

[transmitterdan]

Originally Posted by Dockhead

Interesting that you think it wouldn't have been easier in paper. I did it exactly the way you did, but it would have taken me half the time in paper! But let's keep in mind that this is not on a plotter, but on OpenCPN, which is among electronic means the first among equals . . .



What do you win? Why, the Dockhead Skillful Navigator Prize, of course! Redeemable in as much gin as you can drink on board on a beautiful Baltic evening this summer!

OpenCPN is pretty good at making routes. But when you are finished with your paper plotting you can't see your trip on Google earth with a few clicks. And you have a lot of work still left to enter the waypoints into the nav computer and the backup handheld GPS. And then if you decide to reroute you have all that to do over again. No, I think electronic way is much faster in the long run.

Would be nice to cruise this area in September if all the holiday partiers have gone home.

[Dockhead]

Originally Posted by transmitterdan

OpenCPN is pretty good at making routes. But when you are finished with your paper plotting you can't see your trip on Google earth with a few clicks. And you have a lot of work still left to enter the waypoints into the nav computer and the backup handheld GPS. And then if you decide to reroute you have all that to do over again. No, I think electronic way is much faster in the long run.

Would be nice to cruise this area in September if all the holiday partiers have gone home.

September? The season is long over by then! Remember, this is over 60N! The Scandinavians don't take their holidays in August, like the Continentals, but in July, because August is already getting cooler.

No, the time to come is the last two weeks of June or first two weeks of July, when the light is glorious -- no darkness -- party all night. People don't sleep. You don't have to worry about crowds -- huge country, millions of islands, few people. I only shared an anchorage once with even one other boat in a whole summer here.

[Dockhead]

Originally Posted by sailorF54

I do agree with what is said above. There is one nice feature that I think has not been mentioned. On vector charts (such as CM93) you can set a safety level (I chose 5 m depth) and I had everything shallower painted light blue (between 3 and 5 meters) and darker blue (between 0 and 3 m), using the shallow and deep settings. Now the game is to avoid (wherever possible) the blue patches, follow recommanded routes and stay as close as possible to the rumb line I had also traced on the chart.

Here's my route (done in less than 10', not checked with Google Earth)

Pretty good for 10 minutes!

About a mile longer than TransmitterDan's, but no rocks that I could see

Finding the recommended routes is -- I won't say cheating -- but it's not the main challenge. These are a lot easier to follow at lower zooms, and at higher zooms you know you're not going into a dead end. Maybe I didn't choose the best example. But anyway, good work!

Concerning safety depths -- I have been gradually discovering the power of these. My nav table Zeus, after its update, will now put red check marks across areas with less than the safety depth. Unfortunately, as you zoom out, it covers whole areas with red checks even if there are safe passageway through them. But still, it's useful.

As usual, the implementation in OpenCPN is better, and does really let you see passages through difficult areas, at lower zooms.

[RhythmDoctor]

Originally Posted by carstenb

I realize that, but as you zoom out - the detail on an electronic chart disappears - because the software is telling it to - so screen size doesn't help, unless you rewrite the software.

Before suggesting any software rewrites, are you guys COMPLETELY SURE that you've made full use of the "Chart Zoom/Scale Weighting" slider bar? It sure seems to me that this could address much of what you're complaining about.

And I'm really tired of hearing the "But how and why would you zoom into it if you don't know it's there in the first place?" quote. When I read that months ago I thought (and I still think) that it wreaks of self-serving finger pointing. If you want to be safe, you zoom in on every part of your route to see nearby obstacles. Most would say you should also confirm this on paper charts, though loading raster charts into OpenCPN may accomplish exactly the same thing.

And regardless of what settings you use, I've always followed the same practice for plotting routes: Zoom out to see the whole big picture and plot a crude route that goes over a bunch of obstacles, then zoom in and pan across the whole route using the most detailed chart, inserting additional route waypoints to avoid obstacles. When it's done, reverse the route (to automatically renumber), and reverse it again to automatically renumber again.

When raster charts are available, I think they are vastly superior to ENC for planning, because professional cartographers have made prudent decisions of what details are important and what can be left off. It is less subject to user error than ENC charts, which can be dangerous if the user is omitting certain elements from display.

I think people are way too eager to request complicated features to automate important safety tasks, when they should take it upon themselves to employ prudent practices to avoid obstacles. Based on what I have read, this includes the crew of Team Vestas.

[transmitterdan]

Originally Posted by Dockhead

Finding the recommended routes is -- I won't say cheating -- but it's not the main challenge. These are a lot easier to follow at lower zooms, and at higher zooms you know you're not going into a dead end. Maybe I didn't choose the best example.

The recommended routes are there for a reason so why not use them? Especially when they go the way you want to go.

You guys need to stop using the dedicated chart plotter mind set when talking about electronic charts. Only a masochist would try to plan a voyage on one of those things. A PC is many times faster. You can zoom in and out with the roll of the wheel on the mouse. A decent PC can zoom as fast as you can turn the wheel. You can zoom out, move 50 miles and zoom back in again in 5 seconds.

There simply is no excuse not to zoom in and pan across an entire route. A day's worth of sailing can be panned across in less than a minute at the smallest scale. Even a day's worth of Vestas Wind sailing might only take 90 seconds. IMO the lack of 2 minutes review of their route is why they hit the reef, not because of their electronic charts.

Even though the premise of this thread is flawed it's still a good thread and I hope some good will come of it.

[nohal]

Well... This topic seems a *perfect*subject for a video tutorial on tuning and using OpenCPN (and other available technologies) for route planning
BTW, sailing those waters discussed here is the best thing I did in my life besides the Patagonian channels and Antarctic Peninsula...
FWIW, I still haven't seen anything that can't be done with a bit of tuning of the configuration to one's available charts, local needs and liking. Yes, I know the Garmin autorouting features and have seen them in action between Stockholm and Helsinki. I often thought I must die that very day while looking at the resulting route
And there is (and won't be) *nothing* like a paper chart even if it was just the warm touch of paper and the "Wow, how did they do it?" feeling or the beauty of it hanging on the wall...

Pavel

[seandepagnier]

Originally Posted by transmitterdan

1) Make a rhumb line route for reference.
2) Start a new route working from both ends finding the obvious way in/out of the end points.
3) Then trying to stay as close to the rhumb line but taking the shortest "recommended track" paths connect the start and finish.
4) Once I have both start and finish connected then zoom out and see how it looks.
5) Then pan along the route moving points and adding points close to hazards.

The weather routing plugin can do this automatically.

Originally Posted by sailorF54

I am surprised by the fact that many in this thread seem to be equating electronic charts with VECTOR charts.
But RASTER charts, which are just digital copies of paper charts, are available as well.
Here is an example of the now world famous (at least among sailors) Cargados area thanks to Vestas, on opencpn...
It takes one click to switch from the CM93 vector chart to that (old) NOAA raster chart.

I don't have this old raster chart, where did you get it?

Originally Posted by transmitterdan

Not many dedicated chart plotters have raster chart capability these days. There is no information about depth and other contextual information in a raster chart that a computer can decipher. Many countries have stopped issuing raster charts.

I have an idea... maybe the watchdog plugin could tell you if the active track will run too close to land. Currently it has only a landfall alarm but doesn't consider the active waypoint.

Finally... we really really need plugins to have access to the vector chart depth to improve things.

The counter to that is raster charts can be "self manufactured" using Google Earth or some other satellite imagery database. These are very useful in a lot of situations. I hope OpenCPN will always support this.

Will always have raster support. In the future, more people can have small drones that can get high resolution imagery for charts. Maybe it's even possible for the drones to have sonar to get depth soundings.

[sailorF54]

Originally Posted by boat_alexandra

I don't have this old raster chart, where did you get it?


I have an idea... maybe the watchdog plugin could tell you if the active track will run too close to land. Currently it has only a landfall alarm but doesn't consider the active waypoint.

Finally... we really really need plugins to have access to the vector chart depth to improve things.

The (LOOOO...NNNNG) answer is to be found in this huge thread
(BTW I meant NGA chart, not NOAA)
http://www.cruisersforum.com/forums/...rts-63396.html

From the lot I downloaded before the end of the project, I recently picked up about 90 small scale charts to cover the whole world (including excellent free and legal NZ ones for the Pacific)
BTW, I offered the zipped lot in a French forum to people screaming on how stupid it is to use electronic charts instead of paper charts. Almost no one bothered to download it to have a look... I was not surprised, the debate being often more emotional than rational...

And yes, one can imagine a plugin based on routing techniques that would suggest a route skirting all dangers.
The user would set some depth level, the plugin would default to the next lower continuous depth line if the chosen one is not available and use the 'thumb' rule: never closer than an inch from any danger area re the largest scale chart available). Rather complex to implement, I guess.
and maybe I am just daydreaming...

[seandepagnier]

Originally Posted by sailorF54

The (LOOOO...NNNNG) answer is to be found in this huge thread
(BTW I meant NGA chart, not NOAA)
http://www.cruisersforum.com/forums/...rts-63396.html

Thanks, I will try to find it.

And yes, one can imagine a plugin based on routing techniques that would suggest a route skirting all dangers.
The user would set some depth level, the plugin would default to the next lower continuous depth line if the chosen one is not available and use the 'thumb' rule: never closer than an inch from any danger area re the largest scale chart available). Rather complex to implement, I guess.
and maybe I am just daydreaming...

Well the weather routing plugin already can do it, but maybe what you want is one that checks to verify that your intended route is safe rather than computing a safe route. Not very difficult to implement.

[seandepagnier]

Originally Posted by sailorF54

The (LOOOO...NNNNG) answer is to be found in this huge thread
(BTW I meant NGA chart, not NOAA)
http://www.cruisersforum.com/forums/...rts-63396.html

The thread is 50 pages... any idea which page? I want to download charts for indonesia and the indian ocean if possible. Thanks.

[Dockhead]

Originally Posted by transmitterdan

The recommended routes are there for a reason so why not use them? Especially when they go the way you want to go.

You guys need to stop using the dedicated chart plotter mind set when talking about electronic charts. Only a masochist would try to plan a voyage on one of those things. A PC is many times faster. You can zoom in and out with the roll of the wheel on the mouse. A decent PC can zoom as fast as you can turn the wheel. You can zoom out, move 50 miles and zoom back in again in 5 seconds.

There simply is no excuse not to zoom in and pan across an entire route. A day's worth of sailing can be panned across in less than a minute at the smallest scale. Even a day's worth of Vestas Wind sailing might only take 90 seconds. IMO the lack of 2 minutes review of their route is why they hit the reef, not because of their electronic charts.

Even though the premise of this thread is flawed it's still a good thread and I hope some good will come of it.

The recommended routes marked on the chart more or less solve our problem without resort to our own ingenuity -- I made a mistake by using a place where those are present as an example. If there had been no recommended routes, the task would have been far more difficult without paper, and there are not recommended routes everywhere in these huge archipelagos.

As to Team Vestas -- I agree with you that the cause of that accident was not electronic charts, and I think that's fairly obvious. The guys simply needed to pan through their route -- as they admitted themselves. Nevertheless, a different presentation at low zoom levels could have helped them out a lot.

It's a bit like saying -- that guy ran right into the razor sharp edge at the corner of the nav table and cut himself open -- how stupid was he not to use the handholds, knowing that edge was there. But if the edge had been rounded in the first place, rather than razor sharp? Of course you can't make the whole world fool-proof, but that is not a reason to leave obvious dangerous things lying around.

Concerning chart plotter vs. PC for route planning using electronic charts -- totally agree. It's chalk and cheese, especially with OpenCPN. But many sailors, most, probably, don't have PC navigation programs at all -- just their plotters. Which is a singularly poor tool for route planning -- as you say. But I still think that route planning could be a lot better in OpenCPN -- the reason why I started this thread.

[Dockhead]

Originally Posted by boat_alexandra

Thanks, I will try to find it.



Well the weather routing plugin already can do it, but maybe what you want is one that checks to verify that your intended route is safe rather than computing a safe route. Not very difficult to implement.

I personally am not much interested in automated route planning, even if it is possible to do it well (and not like the Garmin system). I want to understand the route I'm going to be sailing and will miss the chance by not planning it myself. Others may have different points of view.

An automatic check for safety, however, according to programmable criteria, would be great.