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How to build own depth chart?
#1
Is there a way that I can use OpenPlotter to create my own depth chart?

I have a number of uncharted/poorly charted areas as well as shifting sandbars that I would like to chart the depth of so I can find the best route through. Is there a way I can build a depth map with this software, something like many of the fishfinders have now? (Navionics contours, Garmin QuickDraw, etc...)

The other thing I'd really like to do, is be able to put some kind of portable unit on a dinghy and build a depth chart off that, as I really want to go over the area first with my dinghy to find the deep spots instead of grounding my sailboat over and over again. <grin>

Marvin
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#2
You might also ask on the opencpn forum because this is something more suited to a plugin there rather than specifically for openplotter.

So far I do not know of anyone who has done it. It has been a goal for me for a long time now but I am completely sidetracked from making my own depth sounder which needs to happen before I can do this.

It is not an easy problem for a lot of reasons. How do you intend to measure depth? A typical sonar depth sounder works well for knowing approximate depth and if it will become too shallow, but for a survey it can be a problem. This is because the speed of sound travels at different speeds depending on the water temperature. It is impossible to know the water temperature at different depths without dropping a probe and then you might as well use a lead line. This is more of an issue in deeper water, so it is not actually that bad.

To get a really accurate survey I think you either need to use lead line to measure depth, or repeat the survey many many times in different weather.

Another issue is tide compensation. This can be mostly compensated for with lunar tide harmonics, but it is very difficult to compensate for other effects like wind-driven tides, and storm surges. This is a big problem of navionics and many of their user-produced sonar charts also caused the next user to run aground. It's difficult to know or trust the accuracy of whatever sounder is used by whatever user.

So again, multiple surveys of the same area are likely needed if using a depth sounder.


It might be useful for fishing and to get a more detailed contour, but absolute accuracy for transiting areas where you will nearly (but not) touch the bottom is going to be difficult to produce.
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#3
(03-27-2019, 11:17 AM)svMira Wrote: Is there a way that I can use OpenPlotter to create my own depth chart?

I have a number of uncharted/poorly charted areas as well as shifting sandbars that I would like to chart the depth of so I can find the best route through. Is there a way I can build a depth map with this software, something like many of the fishfinders have now? (Navionics contours, Garmin QuickDraw, etc...)

The other thing I'd really like to do, is be able to put some kind of portable unit on a dinghy and build a depth chart off that, as I really want to go over the area first with my dinghy to find the deep spots instead of grounding my sailboat over and over again. <grin>

Marvin

Yet to try it, but I've spend a few evenings with a glass of wine thinking about this..

The most realistic solution to find the best water so far, subject to testing in the real world...

 A little waterproof(ish) case and battery with Pi inside complete with USB GPS and then some way of sending CTRL-M to openCPN from a button. ISTR playing with this a while ago in Node-red and it didn't quite work but with some fiddling looked like it should. Then a fishing rod and float with a weight enough to sink the float and the float set to , say, 2 metres. So then dinghy around the bit of water in question and every time the float went under press the button. That way t least you know where there's enough water (remembering to do this at low tide). 
I think there are also hand held depth gauges which output NMEA so that should work as well, set the logbook to record every couple of seconds and/or use the VDR to record the data then process it by hand later.
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#4
Thanks, that's helpful. I've been wondering how to create consistent data as well. My dream had been that each dataset could be dealt with in isolation and then adjusted as it is 'confirmed' into the master depth file. I can well imagine that this isn't going to be easy.

Is the main OpenCPN forum the one at crusersforum.com?
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