Re: [Maposmatic-dev] Details on why we use Cairo scaling?

[Maxime Petazzoni]

* David Decotigny <address@hidden> [2012-03-25 21:46:19]:

> Since we wanted to control the level of details without having to be
> constrained by the exact mapnik graphical rendering area, we decided to
> render+rescale. We had to determine a good graphical rendering area that
> would be compatible with a predefined zoom level (it's defined in one of
> our config files and related to the google pixels), and then render the
> associated geographical area in it. For example, when asked to render
> Paris, we first compute that the ideal graphical rendering area for a
> zoom level 16 is 64328x57423px (random numbers). Then mapnik
> automagically uses zoom level 16, and stylesheets follow. After that,
> all we had to do was to rescale this into the effective graphical
> rendering area we had, based on the "paper size" we wanted. That was the
> theory, in a perfect world where people don't mess up with the
> transformation matrix...

[snip]

> Max, can you please confirm?

This is what I remember too. Unless we missed it, it seems that (at the
time we wrote ocitysmap2 at least) Mapnik lacked the feature that allows
us to specify the target rendering size *and* the zoom level we wanted.
So we had to go for the latter, and rescale on our own the rendered zone
after the fact -- with the unfortunate side effects that we know.

/Max
-- 
Maxime Petazzoni <http://www.bulix.org>
 ``One by one, the penguins took away my sanity.''
Writing software in California

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