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
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