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Updated Mapnik Output Formats (markdown)

springmeyer 2012-02-24 12:02:36 -08:00
parent 9e9fb9a27d
commit dbe90c6441
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OutputFormats.md

@ -1,8 +1,3 @@
<!-- Name: OutputFormats -->
<!-- Version: 10 -->
<!-- Last-Modified: 2011/09/05 04:32:30 -->
<!-- Author: kkaefer -->
# Mapnik Output Formats
Mapnik supports rendering with both AGG and Cairo (see [[MapnikRenderers]] for more detail), and can create maps or map tiles in a variety of formats.
@ -44,8 +39,23 @@ So to use new format i.e. in python:
or other example in c++:
save_to_file(vw, "test.png", "png256:t=1:c=128");
For more details see [mapnik-devel email](http://lists.berlios.de/pipermail/mapnik-devel/2010-March/001081.html and ticket [#477](https://github.com/mapnik/mapnik/issues/477)
## Hextree details
The m=h (hextree) method should give more smooth images in case of
transparent maps i.e. hybrid like overlayed on some satellite images.
Time and file size increase or decrease depends on content and image
size, but shouldn't be much in common situation. Octree is still the default
for png8 because for most maps without transparent
background or elevation colored/shaded rasters, existing method should
give acceptable and little bit smaller files.
With Hextree, using less than 64-94 colors is not recommended, because returned
palette isn't optimal then. Using 96-128 should give acceptable quality
with some file size reduction, but probably not more then 10%-20%.
For more details see [mapnik-devel email](http://lists.berlios.de/pipermail/mapnik-devel/2010-March/001081.html) and ticket [#477](https://github.com/mapnik/mapnik/issues/477)
## render functions
Most render functions like `save_to_string` also take a third argument which must be a `rgba_palette` object. You can create palettes by passing a buffer with RGBA values (4 bytes), a buffer with RGB values (3 bytes) or an Adobe Photoshop .act file (generated by the "Save for Web" dialog") with exactly 772 bytes to the `rgba_palette` constructors. Note that palette objects are mutable and contain a lookup table that cache all values ever retrieved for faster encoding.