<HTML dir=ltr><HEAD><TITLE>[OSM-talk] JOSM and scale</TITLE>
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<DIV dir=ltr><FONT face="Times New Roman" color=#000000 size=3>Yes, they are probably using the same scale bar for WGS84 and Mercator.</FONT></DIV>
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<DIV dir=ltr><FONT face="Times New Roman" color=#000000 size=3>As far as I know, in WGS84, the scale bar is correct vertically (lat), but in Mercator, that scale bar is wrong both vertically and horizontally if you are far away from the Equator.</FONT></DIV>
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<DIV dir=ltr>As you say, one easy way would be to consider the latitude of, for example, the center of the map when calculating the length of the scale bar.</DIV>
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<DIV>Lucas</DIV>
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<DIV><FONT face=Tahoma size=2><B>De:</B> talk-bounces@openstreetmap.org en nombre de Lars Aronsson<BR><B>Enviado el:</B> mar 25/03/2008 12:41<BR><B>Para:</B> talk@openstreetmap.org<BR><B>Asunto:</B> [OSM-talk] JOSM and scale<BR></FONT><BR></DIV></DIV>
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<P><FONT size=2>At the equator, each degree of latitude or longitude represents a<BR>distance of 111 km. At latitude 60° (N or S), each latitude<BR>degree is still 111 km but since cos 60° = 0.5, each longitude<BR>degree is just half of that or 55.5 km.<BR><BR>In JOSM, when I use the Mercator projection method, look at the<BR>equator and zoom out until the little scale bar in the top left<BR>corner is 111 km, the difference in longitude between the ends of<BR>this bar is one degree. That's fine.<BR><BR>But if I look at 60° N (e.g. Stockholm) and repeat the exercise,<BR>the end points of the 111 km scale bar is still one degree. <BR>That's an error, it should be two degrees. Or rather, when the<BR>bar represents one degree, the label should say 55.5 km instead of<BR>111 km.<BR><BR>I've never cared too much about that scale, but now I know that<BR>these apartment buildings along Syrengatan are 11 x 32 metres and<BR>not 22 x 64 metres as JOSM would lead you to believe,<BR><A href="http://www.openstreetmap.org/?lat=58.407&lon=15.600&zoom=17&layers=0BFT">http://www.openstreetmap.org/?lat=58.407&lon=15.600&zoom=17&layers=0BFT</A><BR><BR>Also, returning to cycle lanes, the "secondary" road<BR>Malmslättsvägen is now marked with cycleway=lane, but this doesn't<BR>show on the map here. And how can I indicate that this bus stop<BR>is only on the southern side of the street (buses going east)? <BR>Buses going in the other direction stop at another place.<BR><BR>"Micromapping" is fun. I want zoom=18 now. Hmmm... and higher<BR>GPS accuracy.<BR><BR><BR>--<BR> Lars Aronsson (lars@aronsson.se)<BR> Aronsson Datateknik - <A href="http://aronsson.se/">http://aronsson.se</A><BR><BR>_______________________________________________<BR>talk mailing list<BR>talk@openstreetmap.org<BR><A href="http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk">http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk</A><BR></FONT></P></DIV></BODY></HTML>