S63 charts - overzoom

[jongough]

Yep, you are right, didn't have my glasses on and saw the blank ID line!

Originally Posted by cagney

Well.... there is actually.

Attachment 91381

Chart 01980456.D has a scale of 1:100.000 .
Switch to single chart mode and hover the cursor over the yellow bar.
So, for some reason, the CM93 chart is of much larger scale than the S63 chart.

Thomas

[jongough]

The AHO really don't care about the reef and the lagoon, no 'real' commercial shipping uses it. However, there is a MAJOR shipping lane that comes in at the NE, goes round the S and then W from the reef. There is normally at least one ship in view at all times going round the reef. So the charts for the shipping lane are good, the ones outside of that, well thats just tough, Captain Cook did a good job!

Originally Posted by bcn

Looking into the charts you are debating it looks to me that the S-63 chart and the CM are using exactly the same underlying data.
For instance all the soundings are identical. The renderings of the coastline/outline of the lagoon are slightly different but the hard points are the same.

So just due the decision of the two chart providers how to present the data we see differences.
- AHS in S-63 says 1:350.000 which results with an overzoom of 1:10 in that 1:39.700 (btw.: the adjacent cells to the West and South show a scale of 1:90.000)
- while CM allows to zoom in up to 1:2200, that's a 1:40 from the stated 1:100.000 scale.

In my opinion there is no reason why CM charts can be over zoomed 40x while S57/S63 "only" 10x.
In our case this would lead to a scale of aprox. 1:10.000, sufficient for your purposes.

The other difference I see between the treatment of CM and S57/S63 charts is that in the case of the CMs the overzoom factor is shown in the status bar, but not for the S57/S63 ones.

[jongough]

For vector charts at large overzoom where OCPN really becomes a 2D plotter, the chart really has little use apart from it is much easier to zoom in and out than to change chart groups, could we not slowly grey out/fade out the charts so that you end up with effectively the 'empty group' chart?

So we would put up the watermark 'OverZoom' for the first couple of steps, perhaps move it to the centre of the chart for the next couple, then start to grey out/fade out the whole chart leaving only the tracks, routes and waypoints as normal. Would this help reduce the confusion as to whether you can navigate on the chart or not? It would allow users to get to waypoints, follow routes/tracks more closely/visually and allow use of the accuracy of GPS.

[bcn]

Funny,

when Renate saw the "blow the horn" overzoom entry her idea was

- horn --> fog
- put a "fog layer" over the screen

More ideas??

[jongough]

In Australia the charts that are available for non-commercial areas are not accurate and you have to use them VERY carefully near land, reef, rocks, etc. Even not using GPS, i.e. standard visual navigation techniques, you will notice that there are issues. You could take sightings on prominent places and fairly quickly determine that what the chart shows and what you can actually see are not the same thing. GPS just exacerbates this.

With the above in mind, I would prefer to see the simplest end user solution to allow greater levels of zoom so that we can use our GPS's to help 'safe navigation'. As an aside I also have a feature request (FS#1533) in to allow the marking of danger areas, so that once found you can make sure you don't 'find' the danger area again at an inconvenient moment!

So, simple is best when allowing overzoom. I know that bouncing around in a yacht in rough sea's and trying to use a mouse with left and right clicks is not the easiest thing. Using the scroll wheel to zoom in/out is OK, just and +/- keys even easier. So a solution that will allow overzoom, smoothly from good for nav to no chart 2D plotter would be useful.

Originally Posted by bdbcat

Guys...

OK, time for my overzoom sermon.

1. We have no way to evaluate the absolute accuracy of any chart, at any
......

Nigel Calder does a much better job of explaining this aspect of charting in his book.
Nigel Calder, How to Read a Nautical Chart - Best Sailing Books
Recommended reading.

2. There is nothing wrong with using OCPN as a "plotting sheet" at super
......

3. It is obvious when using a raster chart at high overzoom that there is
......

4. We can use OCPN as a plotting sheet without charts by making and
.....

So, a reasonable feature request might be to develop a way to reduce the implied onscreen visual accuracy of excessively overzoomed vector charts.

But I will resist requests to allow arbitrary overzoom of all possible charts.

Dave

[fgd3]

Originally Posted by bdbcat

Guys...

But I will resist requests to allow arbitrary overzoom of all possible charts.

Dave

That strikes me as a paternalistic attitude that makes OpenCPN less useful for some navigators. There are times when one might want to navigate to saved waypoints that are too close together at a chart's scale. Without the ability to overzoom on that chart the user has to change charts. With the ability to overzoom all he needs to do is zoom in to check his waypoints and zoom back out to get an overall view.

I know you're trying to keep people from making stupid mistakes but wouldn't it be better to let navigators choose how they want to use OpenCPN to meet their needs?

Fabbian

[cagney]

Originally Posted by jongough

Just to let you know there is a Flyspray feature request for overzoom, FS#1520.

I had coded a solution and submitted it, but I was asked to open raise this question for general discussion.

There are also FS #959 and FS #622, both feature requests concerning over-zooming.

@bcn I haven’t changed my position much since this was last discussed a few years back. Very limited over-zooming of navigation charts, respecting the limit of the original survey. At the same time I think it's great with the new use of the background map as a plotting sheet, as there, of course, are uses for plotting at a very large scale. The suggested gray-out of vector charts at large scale would be interesting to test. No doubt the "situational awareness" should be better than using the background map.

Thomas

[bdbcat]

Guys...

I have prototyped a chart fade, or "fogging" effect on excessive overzoom. It is a linear fade, starting at OZ=10, and the chart detail is completely gone when OZ=30. The screen assumes the blue color of the worl background chart. Zooming can continue for all (now invisible) chart types up until the onscreen scale is about 1/600, depending upon latitude for mercator charts. At 1/600, 2 metres (best GPS accuracy) is about 3 mm, or a bit more than 1/8 inch on screen.

Look for this on github tomorrow, and in the next Beta coming in a few days.

Dave

[dacust]

Originally Posted by bdbcat

Guys...

I have prototyped a chart fade, or "fogging" effect on excessive overzoom. It is a linear fade, starting at OZ=10, and the chart detail is completely gone when OZ=30. The screen assumes the blue color of the worl background chart. Zooming can continue for all (now invisible) chart types up until the onscreen scale is about 1/600, depending upon latitude for mercator charts. At 1/600, 2 metres (best GPS accuracy) is about 3 mm, or a bit more than 1/8 inch on screen.

Look for this on github tomorrow, and in the next Beta coming in a few days.

Dave

This is a very tough situation to deal with. Thanks for digging your heels in and refusing to implement further overzoom until a safe way to do it presented itself. I think you finally have just the right compromise.

-dan

[jongough]

Dave,
Thanks for doing that. I have been looking around to see how a fade could be implemented and I thought changing the alpha channel may have been a way to go for the background charts. The problem is I could not find a place to do it. I seemed to be chasing my tail and getting nowhere.

Looking forward to trying it out.

Jon

Originally Posted by bdbcat

Guys...

I have prototyped a chart fade, or "fogging" effect on excessive overzoom. It is a linear fade, starting at OZ=10, and the chart detail is completely gone when OZ=30. The screen assumes the blue color of the worl background chart. Zooming can continue for all (now invisible) chart types up until the onscreen scale is about 1/600, depending upon latitude for mercator charts. At 1/600, 2 metres (best GPS accuracy) is about 3 mm, or a bit more than 1/8 inch on screen.

Look for this on github tomorrow, and in the next Beta coming in a few days.

Dave

[cagney]

Dave

The new blue-out feature looks very promising. Thank You!
One can now effectively zoom in to a factor of between 15 and 20 for all charts. I would, no surprise here, prefer that the blue-out starts at about a factor of 4 and that the blue out is complete by about 14.

The blue-out is not working for Tmercs.

Thomas

[jongough]

Quick question, is it worth limiting the overzoom to the accuracy provided by the GPS?

If the GPS accuracy is currently 200m then the overzoom could be limited to something sensible for this, if the accuracy is 20m the further overzoom would be allowed. This could be continued down to however accurate the GPS signal is. This would then remove the static zooming limits.

I am not sure if the zoom could be automated to back out if the GPS accuracy was lost. Perhaps I am going down the rabbit hole!

Jon

[jongough]

Dave,
I have just tried the new zoom. It looks good. I then started to play around and an unexpected event occurred.

I set up a route, moved the boat near it (I currently don't have GPS attached to my Linux system), activated the route, move the active point to the next point along, right clicked my boat and selected 'Zero XTE' so that it would navigate straight to the next point. At this point OCPN changed the chart group from 'All' which I had been using to show my CM93 chart, to the 'Empty Group', i.e. only the background map was showing. The new scale (y.yyx) that had been showing numbers now went to (0.00x). I could get back to the All charts by right clicking and selecting them.

Not quite sure what is going on here.

Jon

[bcn]

Jon,

tried to replicate this on our ARM with the latest build (GPS is valid, on shore, well) but CM93 stays - no fall back - and bearing is changed accordingly.

Hubert

[jongough]

Hubert,
I have just done a quick test. If I have and 'Empty Group' chart group I get the effect, if I don't have one I don't. I created the 'Empty Group' earlier as a test for zooming and to allow selecting the background world map rather than having CM93 or S63 charts showing. I probably don't need this with the new fading to allow overzoom, but it is something I noticed.

Jon