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    Re: Cap'n tips
    From: Rick Emerson
    Date: 1999 Feb 15, 00:39 EST

    Steven D. Tripp writes:
     > > One quirk I did see repeatedly is a loss of centering when using
     > > "intellegent zooming".  This feature which is very useful keeps
     > > selecting the most appropriate scale chart for the area being
     > > displayed.  If, for example, you're looking at a 1:40000 chart and
     > > want to zoom down to get a close look at a feature and a 1:20000 chart
     > > covers the area, this chart is brought up automatically.  Conversely,
     > > zooming out will invoke the next smaller scale chart (e.g., 1:80000).
     > > When zooming in, however, occasionally the center of the new, larger
     > > scale (smaller area) chart is no longer anywhere near the center used
     > > with the previous chart.  I was looking at the Portland, ME area and
     > > zoomed in to look at Peaks I but found myself looking at a spot well
     > > to the southwest of there.  I'm not sure *why* this happens and will
     > > accept it may well be an error on my part but it can be frustrating on
     > > occasion.
     >
     > I'm not sure how the Cap'n works, but some of these nav programs do raster maps
     > in this way:  They break up maps into small rectangles for storage and load
     > several (9?) pieces and join them seamlessly on screen.  When you zoom in or
     > out, it takes the clickpoint and tries to find a rectangle at the higher or
     > lower scale and then loads it at the center and loads its surrounding pieces.
     >
     > If your click occurs right on an (invisible) boundary the computer won't know
     > which rectangle to load to the center.  On the other hand maybe the programmer
     > made a mistake in labeling the rectangles.
    The explanation is simpler than that.  When The Cap'n shifts from a
    1:80000 to a 1:40000 chart, it centers the image on the cursor whose
    position can be off-center from simple program use.  The result is the
    offset, which is minor at 1:80000, is now much greater at 1:40000.  I
    don't know the internals of how the shift in chart images is done, but
    I'd opt for passing the co-ords for the prervious image's center
    instead of basing the new image on the cursor location which may have
    shifted.  In effect, there are two events happening here, a "magnify"
    event and a "center image on cursor" event and the latter, IMHO,
    should not happen with a magnify event.  Nautical Technology sees it
    otherwise.
    The quilting you described above is used in Jeppeson's charting
    package and the results, even on a PII 266, were unacceptably slow and
    visually unattractive.
     > Incidently, I am rewriting my Mac navigation program for Windows and UNIX and
     > would be interested in suggestions for features.
    A clean way to show running fixes on the chart would be nice.
    Rick
    S/V One With The Wind, Baba 35
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