NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Cap'n tips
From: Rick Emerson
Date: 1999 Feb 15, 00:39 EST
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 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=--=-= =-= TO UNSUBSCRIBE, send this message to majordomo@XXX.XXX: =-= =-= navigation =-= =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=--=-=