Limit zoom out on Raster charts

[HappySeagull]

oh,and check this out.Per limit of zoom OUT,this hasn't one!in opencpn.I wonder why?
http://www.cruisersforum.com/forums/...tml#post629112

[RhythmDoctor]

FYI, I just encountered this problem tonight with NGA #25609, which I calibrated in MapCal and converted to KAP using the same tools. It is 1:100000, but will only zoom back to TrueScale 57600 on my Win7 desktop. Curiously, I have a similar problem on my WinXP Netbook, but it stops at Truescale 64700. And I just noticed that if I resize the window, the limit changes on both machines. So it seems the window resolution may have a role.

I will try to play with the pixels per inch and scale to see if it fixes the problem, though I my run out of time before I leave for my BVI charter Saturday.

[HappySeagull]

RythmDoctor,
I had to Disable Quilting to get my versions to zoom out a lot ...With Quilting ON, O switched to CM93 after zooming out to 162700 on my 1024x laptop screen.
It will depend on which other charts you have loaded in O...?
Here is scale 80000,(image size 7360x5699) and zoomed seems to have adequate detail.



BSB/NA=Saint Thomas to Anegada (Virgin Islands)
NU=25609,RA=7360,5699,DU=72
KNP/SC=80000,GD=WGS84,PR=MERCATOR
hope that helps...?

[Alisdair]

Originally Posted by wizard-merlin

I've created some Raster charts from paper charts (using Mapcal), scale 1:30000. When I use these with CM93 Vector charts I am not able to zoom out to a sufficient level to get an overview. The max true scale zoom out showing is 16100. Against this, the zoom in is too much getting down to pixel level which is not readable.

I have tried changing the scale in the creation of the KAP file but this seems to make no difference.

How can I make the zoom out level go to a true scale of (say) 100000, whereby the zoom in would be getting into sensible levels?

Is this something to do with pixel setup in the header in Mapcal ?

Not sure what to do next, so would appreciate any help here.

Have you tried setting "Preserve scale when switching charts" on the Toolbox Etc. menu?

[RhythmDoctor]

Originally Posted by HappySeagull

RythmDoctor,
I had to Disable Quilting to get my versions to zoom out a lot ...With Quilting ON, O switched to CM93 after zooming out to 162700 on my 1024x laptop screen.
It will depend on which other charts you have loaded in O...?
Here is scale 80000,(image size 7360x5699) and zoomed seems to have adequate detail.

Attachment 52190

BSB/NA=Saint Thomas to Anegada (Virgin Islands)
NU=25609,RA=7360,5699,DU=72
KNP/SC=80000,GD=WGS84,PR=MERCATOR
hope that helps...?

Switching off quilting and adjusting the DU value had no effect for me, and I ran out of time to experiment more before I had to leave for BVI. But I was able to use the NGA charts even with the zooming problem, and they were much more accurate than NOAA #25641.

After I returned from BVI I did some more experimentation, and discovered that after upgrading to OpenCPN 3.1.13x9 beta, the behaviors that you described happened. Before that I was using 3.0.2, which appears to behave differently. With 3.1 beta, turning off quilting allowed zooming way out, just as you show.

One other change I made was to reduce the size of 25609 by 50% (like you apparently did), and that allowed for zooming out further than before with quilting on. Apparently with quilting on, OpenCPN has a limit to how far it's willing to condense pixels before going to a different chart, and reducing the chart size in a photo editing program helps to overcome that limitation (at the expense of some resolution). However, I suggest that reducing the size of the chart should be accompanied either by a proportional reduction in DU or proportional increase in SC. IIRC, the DU value is automatically calculated in the KAP file utility from SC and the calibration data when it generates the .hdr file, so I think it's best to set SC in the CHARTCAL.DIR file prior to generating the .hdr file, and let the KAP utility calculate DU. I'd be concerned that manually tweaking DU in the .hdr file might cause something else to break.

[HappySeagull]

yes, sorry. I'm a beta guy and forget to coordinate versions! There have been improvements, because it seems lots of people want to see the whole chart.
Your point SC vs DU is well taken. I was wont to changing scales in the header without due consideration, hacking is the apt term, but only as a fast experiment.
I'm interested in what you can come up with in a formulaic way (with the Kap-making utility you are using?) to get charts "in order" and quilting smoothly and intuitively.
I take the scale directly from the paper chart's header, in lieu of thinking about it because, ideally, the final result is similar to poring over the real chart without making the image bigger than it need be to do this. ie:inspecting any 1:1250000 chart with a magnifying glass is stupid, beyond useful detail- "overzoomed" it should go "jaggy" on a computer screen.