On Wed, Jun 09, 2010 at 11:55:45AM -0700, we recorded a bogon-computron collision of the <[email protected]> flavor, containing: > > Thanks to Jerry Dunmire, KA6HLD, we now have Open Street Map support > in Xastir. Woohoo! > > For an interesting place to look, zoom in on a border and see what > differences you can find for roads crossing said border. For the > main Canadian border crossing north of me I can't see any difference > in the roads at all. > > Thanks Jerry!
This is very good stuff, as the OSM maps do look really nice, and probably won't suffer from the very stupid projection issues that the Census TIGER data had. That said, the second I tried it I got a map that wasn't lining up with other data I had. At first I thought this was an issue with the server returning a different geographic region than the one requested, because I've seen the same thing happen with terraserver aerial photos, if trying to view too big a map at particular zoom levels. But rather, it seems to be an issue with how the OSM code tries to restrict our zoom level to those that match OSM levels. Here's an example, using my 1261x1019 map window: http://www.swcp.com/~russo/xastir_osm/bad_view.png This particular view is actually one of my map bookmarks, showing the area where most of the APRS activity is near me. The bookmark sets zoom level to 131 and the center to 35d04.715'N by 106d29.866'W. The image is a screenshot showing the OSM layer with a county-provided road shapefile drawn on top. The orange road running diagonally from center-right to lower-right is the OSM representation of NM state road 337, which is represented in black to its left from the county GIS files. The county one is right --- it shows my Igate (KM5VY-10) in the correct relation to roads. Other roads look wrong, too --- compare the sorta reddish major streets in Albuquerque from OSM to similarly-shaped, but differently-scaled, roads in black from the county shapefile. Zooming in even just a tiny bit, as by selecting just the area inside the map boarder, makes the server return precisely what is asked for and the downloaded map line up very nicely with the county data: http://www.swcp.com/~russo/xastir_osm/good_view.png FWIW, when run with debug level 512, the OSM code prints out: left side is -106.777989 right side is -106.217544 top is 35.263983 bottom is 34.893183 lat center is 35.078583 long center is -106.497767 screen width is 1261 screen height is 1019 map width is 0.560444 map height is 0.370800 scale_y = 131 scale_x = 160 zf = 11.627562 z = 12 in the first (bad) case and left side is -106.715161 right side is -106.280817 top is 35.223122 bottom is 34.934406 lat center is 35.078764 long center is -106.497989 screen width is 1261 screen height is 1019 map width is 0.434344 map height is 0.288717 scale_y = 102 scale_x = 124 zf = 11.995294 z = 12 in the second (good) case. I also note that the code appears to be changing requested zoom levels to match OSM zoom levels. This may or may not be desirable (I was puzzled when I tried to set a custom zoom level to a particular value, and the code repeatedly set it to something else). And now that I say that, I see where the problem must be. I note that when I *tried* to set zoom level to 131 by hand (using the "Custom zoom level") it wouldn't do what I asked, but when I chose my map bookmark it did actually go to that zoom level --- perhaps the actual issue is that Xastir is really using my selected bookmarked zoom level despite the OSM code's attempt to restrict to OSM zoom levels. As soon as I try to zoom in by selecting the area inside the border, the code that restricts to OSM levels actually does work, and therefore the map I see after the zoom is done looks good. It just seems to be bookmarks that are busted (because the restriction to specific zoom levels isn't respected). Not sure where to look for that mistake, but it would explain why I'm getting bad OSM maps at my bookmarked view. Rather than try to restrict the allowed zoom levels, it might be better to pull in an image of a nearby OSM level and then rescale it to the requested Xastir zoom level. That's what the terraserver and other .geo code does. Regardless, it's cool that OSM is usable now. If it were more easily adapted for use with user-selected zoom levels (especially those in bookmarks), it' be even better. -- Tom Russo KM5VY SAR502 DM64ux http://www.swcp.com/~russo/ Tijeras, NM QRPL#1592 K2#398 SOC#236 http://kevan.org/brain.cgi?DDTNM "It is better to live on your feet than to die with your knees." -- Mil Millington on running, in Instructions for Living Someone Else's Life _______________________________________________ Xastir mailing list [email protected] http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
