Martin, I don't think this user was worried about "what happens near the poles". He said "whole world" meaning most of it. I know geotools has problems just displaying data, e.g. antarctica, in mercator since we don't smartly cut and sew the polygons in the viewing area. So are you perhaps misreading what this user is trying to say to us?
cheers, adrian On Mon, 2007-05-14 at 18:09 -0400, Martin Desruisseaux wrote: > 新买 a écrit : > > Yes, with Mercator Projection, only the part where latitude between > > -85 to 85 can be rendered. I trace the code of Mercator Projection, > > there is some code as "throw Exception...". > > I try to comments these word, then it dont work. > > May you solve this problem?\ > > As explained in my previous email, you can NOT display a map up to 90°N or > 90°S > using Mercator projection, no matter which software (mapXtreme or whatever) > you > use. This is mathematically *impossible*. The formula for the spherical case > is: > > log(tan(PI/4 + 0.5*latitude)) > > With latitude = PI/2, we get > > log(tan(PI/4 + PI/4)) = > log(tan(PI/2)) = > log(sin(PI/2) / cos(PI/2)) = > log(1 / 0) = > log(infinity) = > infinity > > See also Wikipedia: http://en.wikipedia.org/wiki/Mercator_projection > > "A Mercator map can never fully show the polar areas, since linear scale > becomes infinitely high at the poles. (...snip...) At latitudes higher > than 70° north or south, the Mercator projection is practically unusable." > > The "throw Exception" is there as a guard and even the 85° limit (before > throwing an exception) is a lot. > > If you see a world map with latitude up to 90°N or 90°S, then this is not a > Mercator projection. It may be a Plate Carre or something else, but *not* a > Cylindrical Mercator. > > Martin > > ------------------------------------------------------------------------- > This SF.net email is sponsored by DB2 Express > Download DB2 Express C - the FREE version of DB2 express and take > control of your XML. No limits. Just data. Click to get it now. > http://sourceforge.net/powerbar/db2/ > _______________________________________________ > Geotools-gt2-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/geotools-gt2-users ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ Geotools-gt2-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/geotools-gt2-users
