Is there an option to configure "Chart Quilting" ?

[bdbcat]

Martin...

I cannot reproduce this effect with NOAA charts. The scales match, reasonably, and OCPN does the right thing naturally.

Can you ZIP up and send me the charts shown in your screenshots? I don't need the wide area, just the few around your area of interest.

Thanks
Dave

[BlueShip]

Dave,

you have a message with a link for a small map stack.

Thank you
Martin

[bdbcat]

Martin...

Got them. On my punch list for today.

Thanks
Dave

[BlueShip]

Good luck,

I noticed this effect also for KAPs (not stacked) in combination with the background chart.

Martin

[bdbcat]

Martin...

I looked at this a little bit today.
I believe the real anomaly is the behavior of O46 on ZOOM-OUT.

Please bear with me as I describe some of the rules OCPN uses to select which charts to include in the quilt.

Definition:
The "Reference" chart is the left most (largest scale) highlit button in the chart bar.

Starting from your standard screenshot 41.
You can always select a larger scale chart as reference chart by tapping on the appropriate chart-bar blue button. Or you can use the toolbar tool, 3rd and 4th buttons to change the reference chart. Or this may happen automatically if the zoom-scale slider bar is set to factor 2 or greater.

By one of these methods, you can get the display that you want.

However, with current O4.6, when you zoom out from there, one of the rules for selecting the correct reference chart for the new zoom level is this:

For Raster charts, the reference chart on zoom out must cover the center point of the screen.

So, when you zoom out, you will potentially lose the larger scale reference chart that you were using. And then when you zoom back in, you will have to reselect your desired reference chart as noted above. Not too friendly, in your particular situation, with charts of nearly but not exactly equal scales.

That particular rule comes from legacy code which did not have our more modern OpenGL raster tile caching. The rule exists in order to provide acceptable performance on zoom out, when many, many more charts may appear on screen, depending on the chart availability at a particular location.

This is all one of the challenges of a rules-based approach to chart quilting. It is always possible to find a pathological case where a human would do a better job, no matter how we tweak the rules. But we really don't want too many control knobs for the user to twiddle, lest the UI becomes unwieldy.

So, for O4.6.1, I will relax this rule, at least when OpenGL is active. This should give you the desired result, or at least come closer to your expectations.

Thanks
Dave

[BlueShip]

Dave,

thank you very much for your effort. You are right to keep the interface clean and simple. But in my opinion the interface is not as intuitive as it could be in this situation. I do not want to stress your nerves but want to make a suggestion.

Zoom in and zoom out are not the problems. The user is directly involved and one can see what is going on during zooming. As I understood these actions determine the reference chart (has to cover the center of the screen and should correspond to the actual scale). Up to here everything is intuitive and the chart bar contains the charts I would expect. Nothing has to be changed.

Unexpected is only the selection of displayed charts. I would expect a selection corresponding to the "master scale" of the reference chart. This could be done even post zooming (performance during zooming is not touched). The same behavior could be implemented for panning.

My suggestion:
1. The scale of the reference chart should be a kind of "master scale". The master scale is fix and only changed by zooming in/out.
2. The charts within the chart bar are checked concerning their scale and the best matching charts are visualized.
3. This behavior could be set by a check box "keep master scale" as an option on the tab of each chart group.

Martin

[bdbcat]

Martin...

All well and good, but as they say, the devil is in the details.

The reference chart scale is the "master scale". If a chart scale is strictly larger than the master scale, it is not shown. That is the rule, no matter how close the scales are. Larger is larger.

2. The charts within the chart bar are checked concerning their scale and the best matching charts are visualized.

Key word here is "best". That implies goal-seeking, and everyone has different ideas of what is "best". For instance, the super high resolution images you have used would not be appropriate for a low performance system like an older XP laptop, or an rPI system.



You can see the zoom-out problem easily.
1. Start OCPN, select as a reference chart a raster chart which does not cover the center point.

2. Zoom out. You may lose the reference chart, even with a small zoom by ALT-PGUP.

The whole idea needs some more thought. Changes would potentially require extensive regression testing. So I can say for sure that there will not be any major changes in this behavior for OCPN 4.6.1 maintenance release due shortly.

Thanks
Dave

[BlueShip]

Dave,

ABS(Scale1-Scale2) > Precision of Chart Group Scale instead of Scale1-Scale2 > 0 ?

Martin