Support dynamic pixels

[artemp]

the assumption of '0.00028' meter pixel is based on the OGC SLD spec and assuming a screen ppi of around 90.1 pixels per inch, which of course is not always the case depending on screen resolution/size. So we need to properly investigate exposing to the user the ability to set this option.

source:trunk/src/scale_denominator.cpp#L37

{{{

from mapnik import Map
m= Map(256,256)
m.scale_denominator
-8834880.2216889616
m.pixel_size # in units of projection
0.00028
m.pixel_size = 0.00030
m.scale_denominator() # would change...
}}}

[artemp]

[artem] we shouldn't assume that pixels are square :
{{{

m.pixel_size
(0.00028,0.00020)
}}}

[artemp]

[springmeyer] see also #389

[artemp]

[springmeyer] Latest SLD spec is now called 'Symbol Encoding' and can be downloaded (1.1.0) from: http://www.opengeospatial.org/standards/symbol

[springmeyer]

not actionable