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Old 17-09-2012, 03:41   #1231
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User Contribution of Depth Soundings into a Layer

Currently we are cruising around the Ionian and I find that there are many stretches of the coast that have almost no charting. For example, around most of the coast of Paxos and Anti-Paxos there are no depth soundings on either my CM93 nor my up-to-date C-Map on my chartplotter.

However, here am I cruising around with both a GPS and a depth sounder constantly in action, essentially doing my own survey as I sail.

So, wouldn't it make sense to harvest all this data - ie depth reading coupled with GPS location - in order to update the charts?

Since we have hundreds of people cruising around using openCPN, and many of them have NMEA inputs from their instruments, including depth sounders, is there some way that people could:
a) update their own chart using their own data, and
b) upload their data to a central repository, thus making it available for other people to update their charts?

Obviously there would need to be some parameters. People would have to make sure that their soundings are from the water surface, not below keel (so some calibration factor would have to be entered into the software somewhere). Ideally we would also have an adjustment for the horizontal distance from the sounder to the GPS receiver (thought that should be pretty minor). They would also need to input the maximum depth that their equipment can handle (eg 100m). And then there needs to be a celestial adjustment to account for tide and to try to reduce the reading to lowest astronomical tide.

But it seems to me that those would all be pretty simple.

We would also need to de-clutter (don't need a sounding every meter), and also resolve conflicts (if multiple people are uploading data for the same place, but give different readings).

This aggregated data could then be downloaded by people, presumably as a layer that they superimpose on their chart, with something to take into account chart offsets, as the layer would be be WGS84.

Over time I would think this would make our charts a whole lot more detailed!

Unfortunately I am not a programmer, so can't put this together myself.

Thoughts?

Noel

PS Just a quick broken link: On Layers Library | Official OpenCPN Homepage the link to the manual to read about layers doesn't work.
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Old 17-09-2012, 06:57   #1232
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Re: Feature Requests

Noel,
It is a good idea that has been discussed a few times, among other places, in the OpenCPN threads.

You have mentioned some of the pro and cons. I think the bottom line has been summarized as that none has come up with a system to take care of the quality in such a system.
There is need for a good algorithm to do the things you consider regarding quality:
- How to make sure the soundings are logged from the waterline.
-How to handle the water level due to wind and tide
-How to handle conflicts.

I still think that it would give valuable information. If nothing else, a conservative approach were the smallest depth is used to mark areas of reduced depth, and a way to clearly indicate these much less trustworthy soundings in OpenCPN could be of great value in areas where there are no soundings at all, and it is unlikelly that anyone will perform a proper charting operation.

An additional complication is that private charting is illegal, for example in Sweden, although this is probably about to change in the future.

In any case, it would be a great addition to OpenCPN to be able to chart your favourite bay for private use.
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Old 17-09-2012, 07:36   #1233
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Re: Feature Requests

As you say, in areas where there is no information, then some would be better than none. If it is done as a layer, then people can enable the layer only if they want it, knowing that the data should be considered unreliable. As it is, I tend to treat all my chart data as somewhat suspect anyway. Several times, it seems, my boat has had the ability to cross over solid dry land!

Shouldn't be too hard to have a system that labels the confidence of data - eg multiple soundings all within 5% of each other is more reliable than a single one. Simple statistical analysis will identify outliers and confidence levels. Erring on the side of shallow rather than deep will also help.

Could be done as a plugin I guess. Just depends if there is anyone out there with both the skill and the inclination to put it together!

Noel
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Old 17-09-2012, 10:20   #1234
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Re: User Contribution of Depth Soundings into a Layer

Quote:
Originally Posted by LifePart2 View Post
Currently we are cruising around the Ionian and I find that there are many stretches of the coast that have almost no charting. For example, around most of the coast of Paxos and Anti-Paxos there are no depth soundings on either my CM93 nor my up-to-date C-Map on my chartplotter.

However, here am I cruising around with both a GPS and a depth sounder constantly in action, essentially doing my own survey as I sail.

So, wouldn't it make sense to harvest all this data - ie depth reading coupled with GPS location - in order to update the charts?

Since we have hundreds of people cruising around using openCPN, and many of them have NMEA inputs from their instruments, including depth sounders, is there some way that people could:
a) update their own chart using their own data, and
b) upload their data to a central repository, thus making it available for other people to update their charts?

Obviously there would need to be some parameters. People would have to make sure that their soundings are from the water surface, not below keel (so some calibration factor would have to be entered into the software somewhere). Ideally we would also have an adjustment for the horizontal distance from the sounder to the GPS receiver (thought that should be pretty minor). They would also need to input the maximum depth that their equipment can handle (eg 100m). And then there needs to be a celestial adjustment to account for tide and to try to reduce the reading to lowest astronomical tide.

But it seems to me that those would all be pretty simple.

We would also need to de-clutter (don't need a sounding every meter), and also resolve conflicts (if multiple people are uploading data for the same place, but give different readings).

This aggregated data could then be downloaded by people, presumably as a layer that they superimpose on their chart, with something to take into account chart offsets, as the layer would be be WGS84.

Over time I would think this would make our charts a whole lot more detailed!

Unfortunately I am not a programmer, so can't put this together myself.

Thoughts?

Noel

PS Just a quick broken link: On Layers Library | Official OpenCPN Homepage the link to the manual to read about layers doesn't work.
NOEL,

Your idea is supurb, and the details should be able to be worked out. For example, user generated data could be shown in different colors to identify the quality of the data. Data that is in conflict could be resolved in several simple ways - data with differences in value of less than 10% could be averaged, while data with more than 10% discrepency could be discarded. Perhaps all user generated data could initially be shown in red, and then in a different color if 10 or more instances of that data are submitted and agree within less than 10%. But the basic principle of gathering the data is sound. Of course, the layer(s) containing user generated data must be clearly labeled as such, so that it's reliability is clearly understood. That layer also needs to be a selectable option.
Bravo!
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Old 17-09-2012, 10:33   #1235

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Re: Feature Requests

I think that could be implemented in an incremental fashion. That is, get the project started and ignore the difficult parts like correcting for surge or unknown tidal state. Add those corrections to the final equations when and as the task becomes possible, in the theory of "half a loaf is better than none".

And because yes, this could be dangerously confused with more reliable data, put the "user supplied depths" on a separate layer, which is initially set to a different font (size, style, color, selectable by user) and perhaps also has a "blink" attribute set, so the unverified depth soundings blink on the screen, making them impossible to confuse with charted ones. (Of course, user selectable again.) Make it clear by default that this is potentially unreliable data, and let the user change that to whatever they are more comfortable with.

But compared to the programming and display tasks, I think there's still a more formidable stopper. How many recreational sailors have their fathometers supplying an NMEA stream, or other digital data stream that can conveniently be saved and exported along with time and position??

"Several times, it seems, my boat has had the ability to cross over solid dry land!"
Noel, check your chart dates. If they are more than a thousand years old, you've got to add significant offset for a rising sea level. <VBG>
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Old 17-09-2012, 16:21   #1236
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Re: Feature Requests

Guys, You should have a look at Hydrographic survey plugin by nohal:
Hydrographic Survey Plugin
And chime in there if you can improve the plugin ;-)
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Old 20-09-2012, 05:09   #1237
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Re: Feature Requests

Thanks Seth! Didn't realise the project had already been started! That is so cool!

Hellosailor: yes, my charts are the latest updates from C-Map. The offsets are not large, maybe 100 meters or so, but enough to put me on land instead of water in Mahon bay, Menorca
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Old 20-09-2012, 11:31   #1238

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Re: Feature Requests

Noel, could those offsets be due to chart datum choices, or perhaps from the last survey having been done in Roman times? (So to speak.)

I've seen more recent ones in well-known parts of the US, where the "latest" USGS survey information is 1/3 mile off from GPS positions. Sometimes, some places, no one bothers to update.
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Old 20-09-2012, 13:48   #1239
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Re: Feature Requests

Quite possible. I haven't entered any offsets, so the chart is just as it came from Jeppesen and plugged into my Standard Horizon chart plotter, so presumably it is just an old survey from British Admiralty times!
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Old 20-09-2012, 17:25   #1240

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Re: Feature Requests

An Admiralty chart might explain it. After all, the Admiralty might still be po'd at the Spanish about that Armada. <VBG>
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Old 25-09-2012, 03:37   #1241
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Re: Feature Requests

Wouldn't it make more sense to have this thread as a sub-forum, with each feature request having its own thread in that forum?
That would make it much easier to follow the discussion about a feature, and a lot less likely for a feature to get buried and lost.


Just a thought

Noel
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Old 25-09-2012, 03:44   #1242
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Lightbulb Polar Diagrams Plugin

I would like to suggest a new plugin - if I were a programmer, I would do it myself, but unfortunately I am not, so I am hoping someone will be inspired enough to do this.

What I would like is a plugin that builds up a polar diagram for my boat for all wind speeds and all my different sail plans. Since I have NMEA input from my wind speed, wind direction, boat speed and GPS, this should not be too difficult to do. Here are some of the features I would like to see:

Benefits

There are several pieces of useful information that one could get from the plugin, once data has been built up. For example:
1) The wind is X kts and I need to sail dead downwind - am I faster if:
a) I sail a dead run with just the spinnaker and no white sails or
b) Tack downwind with main and spinnaker at 130 deg apparent?
2) Wind is X kts and I want to sail a course of Y deg. What is my optimal sail plan?
3) The wind is X kts. I need to sail dead upwind and am in a hurry to get to the anchorage before dark. Should I:
a) take down the sails and just motor straight upwind
b) leave up the main, but not the jib, and motor sail at 30 deg apparent
c) leave up full sail and motor sail at 40 deg apparent
d) turn off the engine and just sail

(to answer this and other upwind VMG questions we would want to calculate leeway by using the GPS data in addition to the boat speed data.)

Ultimately one could also build a passage planning plugin that would take a route plotted on openCPN, combine it with GRIB file information plus the polar chart info and produce a suggested optimal passage route with apparent wind / magnetic course routing and optimal sail plan - and projected ETA.

As an added feature, my data could be uploaded to a central server and averaged with data from other boats identical to mine to provide an average for the boat model. Then when people ask 'how fast does a 'brand x' go?' the answers will be right there.

Features


Settings
Enter type of boat (over time we could build up a drop down list)
Select available sails. Here people would select the sails available to them in their sail locker - eg Genoa 1, Genoa 2, Storm Jib, Gennaker, Asymmetric spinnaker, Symmetrical spinnaker, Main (forward), Main (aft), Mizzen, Engine, Engine (port), Engine (starboard). These could be presented as checkboxes with the option to add additional sails (eg topsail if they happen to be in a square rigger) or change the description of the sail.

Operation.
When enabled, the plugin would show its status on the screen, including the current sail-plan, with a 'Stop' and 'Start' button which would stop or start the recording of information. The start button would also ask for a confirmation of current sail plan.

There would also be a 'Change Sails' button. When pressed, that would automatically stop the recording while you enter the new sail plan, and then start recording again when the 'done' button is pressed. I would suggest that the sail plan be displayed a a set of checkboxes so you just check the box for Jib and Main and press 'done'. Probably it should also have a dialogue to enter the time for the end of the old sail plan and the start of the new sail plan. That way you could enter the data after you reefed, and have it remove the last 15 minutes of recording while you were messing about doing the reef.

The options in the 'change sails' dialogue would include actually changing sails - eg putting up the spinnaker - as well as changing the reefs on a specified sail. The engine would also have the options for 'cruising', 'semi-fast', and 'fast' - or this could be specified as rpm.

While the plugin is recording data, it combines the current speed with the current true wind speed and direction. It records this as a linear record. It then averages this data point with previous data points for the same wind speed, direction and sail plan, and saves that in a separate database.

Thus, over time, one builds up an average boat speed for any given set of conditions of wind plus sail plan (including the engine as a sail).

I would suggest that the program also checks the current data with the data from, say, 15 seconds ago. If there is a significant change of direction (eg > 20 deg) then the data from 15 seconds ago until the data stabilizes on a new direction would be excluded from the calculations. This would eliminate errors caused by, for example, tacking, gybing or broaching. Perhaps the same should be done if the wind speed changes dramatically, so as to allow the boat time to accelerate or decelerate to the new wind speed.

It should also stop recording if the boat speed (and maybe wind speed) drops below a certain limit - eg 1kt - so as to not distort the averages when you aren't actually sailing but forgot to turn off the recording. For example you are anchoring or heaving too.

In a later iteration, I would suggest we include GPS data so that we can calculate leeway. Of course we would have to figure out how to exclude current and tide from affecting this. Or maybe the 'include GPS' data would be an additional option to be used only when we know we are in current-free waters.

Data Editing
Suppose one sets the plugin to record, and then you change sails or switch on the engine but forget to tell the plugin?

There would need to be an option to exclude the data between two time points. Ideally it would be nice to display the speed on a graph as that would help one to spot when you made the change, but at the minimum you just need to enter in a beginning and end time and the plugin would exclude that data from the calculations and recalculate the averages.

That way if you suddenly realise you have been motoring for two hours at 6kts but the plugin thinks you are sailing with full sail in 2kts of wind you would be able to remove that erroneous data.

Output
Initially just a digital interface would be sufficient. Ultimately it would be nice to actually display graphical polar charts, but that is probably less useful than having a dialogue.
Mostly one would want to ask for:
a) optimal sail plan for a given wind and bearing
b) expected speed and ETA for a given destination, wind, and sail plan
c) expected VMG for given destination, wind and sail plan

later one could add:
d) display / export as jpg or pdf / print the polar charts
e) upload to central server to combine with others
f) comparative VMG - better to run or tack downwind? Better to pinch, or sail free and fast?

So, any takers? What do you think?

Noel
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Old 25-09-2012, 08:55   #1243
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Re: Feature Requests

Dear Noel,

That's a lot of programming you outlined, but it would be a convenient organizer and recorder, replacing something that can be only approximated by hand.

You will find that with the increased accuracy the data will be varied due to such things as flat or heavy sea conditions, weight of the boat, how fouled the hull is, who is at the helm, how tight you have your headsail halyard, and as you point out, which sails are up and how they are trimmed. Therefore you will need to identify, sort and average this data in order to be able to use it. Being able to record the data and identify it with comments would be very helpful.

Finally you will need to make a decision as to what average number to put into the particular polar (perhaps broken into different sail plans and sea conditions), something that needs to be done when one builds a good polar by hand. I wonder if this can really be made automatic, based on averages of the selected data, somehow.

Of course the polars will need to get modified through time to improve them. How could that be done? Target Boat Speed as,well as VMG?

This would be a big effort I think...
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Old 25-09-2012, 09:51   #1244
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Re: Feature Requests

Hmm, didn't seem that big of a job to me. Just collecting data points and averaging them out - independent variables being the wind speed and direction and sail plan, dependent variable being boat speed (and perhaps leeway)

Of course the performance would vary with all those other variables. I wasn't thinking of accounting for them - just having an average for wind speed, direction and course sailed. After all, we are cruising, not racing. :-)

The actual polar diagram is, in my opinion, less important than the averaged data that one can query. As with existing polar diagrams, one would have a different one for each sail plan. Which is why, again, the digital data that can be queried is more important than a graphic.

Today, for example, I found that in 10-12 kts of wind I sail better upwind at 42 deg apparent than at 39. Found that out because another boat happened to be on exactly the same tack as me, a mere half mile away, doing the same speed as me and I could track our relative positions by radar. Without someone to 'race' again, I wouldn't (and didn't) have known that. But the plugin might have told me.

Anyway, as I said, if anyone is interested enough to work on it, I think it would be rather cool.
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Old 25-09-2012, 16:14   #1245
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Re: Feature Requests

Of course, I agree with you.
Maybe we could start by figuring out an efficient way of getting there using a Nema data stream, what sentences are needed, how a simple interface might work, what options and controls would be needed, what the screens might look like-You've already started it! Refine your suggestions so that when there is someone who has time, they can refer to it. Then upload it to this thread.
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