[OSM-dev] Projection calculation
Milo van der Linden
mlinden at zeelandnet.nl
Mon May 19 22:08:35 BST 2008
Hello Wayne!
There is no "easy" way for doing coordinate transformations since there
is a lot you have to take into account. I am not sure what programming
language you want to use, but if it is Javascript you might dive into
proj4js http://proj4js.org/ and see if it offers libraries you can use.
Good luck,
Milo van der Linden
Wayne Walker wrote:
> I'm not using slippy map. For the project I'm doing I need static
> images. I just can't sort out the math to find the veritcal position in
> the tile map. I've tried mercator projection but I'm missing something.
>
> I've tried to follow the logic in the javascript of the slippy map, but
> without comments and with short var/function names I get lost.
>
> Does anyone have a simple formula such that:
>
> y = ....(lat)?
>
> I've tried things like:
>
> k = 4.0
> y = log(tan(y*Math::PI/180.0) + 1/cos(y*Math::PI/180.0))/k
>
> Which is the mercator projection formula (substituting 1/cos for sec)
> from wikipedia.
>
> Also tried a Miller cylindrical projection as that seems much more like
> what the main tile looks like.
>
> miller=2.30341254337639
> y = 1.25 * log(tan(Math::PI/4 + 0.8 * (y*Math::PI/180.0)/2))/miller
>
>
> No joy there either.
>
> Any ideas?
>
>
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