| TileStache.Core | index |
The core class bits of TileStache.
Two important classes can be found here.
Layer represents a set of tiles in TileStache. It keeps references to
providers, projections, a Configuration instance, and other details required
for to the storage and rendering of a tile set. Layers are represented in the
configuration file as a dictionary:
{
"cache": ...,
"layers":
{
"example-name":
{
"provider": { ... },
"metatile": { ... },
"preview": { ... },
"projection": ...,
"stale lock timeout": ...,
"cache lifespan": ...,
"write cache": ...,
"bounds": { ... },
"allowed origin": ...,
"maximum cache age": ...,
"jpeg options": ...,
"png options": ...
}
}
}
- "provider" refers to a Provider, explained in detail in TileStache.Providers.
- "metatile" optionally makes it possible for multiple individual tiles to be
rendered at one time, for greater speed and efficiency. This is commonly used
for the Mapnik provider. See below for more information on metatiles.
- "preview" optionally overrides the starting point for the built-in per-layer
slippy map preview, useful for image-based layers where appropriate.
See below for more information on the preview.
- "projection" names a geographic projection, explained in TileStache.Geography.
If omitted, defaults to spherical mercator.
- "stale lock timeout" is an optional number of seconds to wait before forcing
a lock that might be stuck. This is defined on a per-layer basis, rather than
for an entire cache at one time, because you may have different expectations
for the rendering speeds of different layer configurations. Defaults to 15.
- "cache lifespan" is an optional number of seconds that cached tiles should
be stored. This is defined on a per-layer basis. Defaults to forever if None,
0 or omitted.
- "write cache" is an optional boolean value to allow skipping cache write
altogether. This is defined on a per-layer basis. Defaults to true if omitted.
- "bounds" is an optional dictionary of six tile boundaries to limit the
rendered area: low (lowest zoom level), high (highest zoom level), north,
west, south, and east (all in degrees).
- "allowed origin" is an optional string that shows up in the response HTTP
header Access-Control-Allow-Origin, useful for when you need to provide
javascript direct access to response data such as GeoJSON or pixel values.
The header is part of a W3C working draft (http://www.w3.org/TR/cors/).
- "maximum cache age" is an optional number of seconds used to control behavior
of downstream caches. Causes TileStache responses to include Cache-Control
and Expires HTTP response headers. Useful when TileStache is itself hosted
behind an HTTP cache such as Squid, Cloudfront, or Akamai.
- "redirects" is an optional dictionary of per-extension HTTP redirects,
treated as lowercase. Useful in cases where your tile provider can support
many formats but you want to enforce limits to save on cache usage.
If a request is made for a tile with an extension in the dictionary keys,
a response can be generated that redirects the client to the same tile
with another extension.
- "jpeg options" is an optional dictionary of JPEG creation options, passed
through to PIL: http://www.pythonware.com/library/pil/handbook/format-jpeg.htm.
- "png options" is an optional dictionary of PNG creation options, passed
through to PIL: http://www.pythonware.com/library/pil/handbook/format-png.htm.
The public-facing URL of a single tile for this layer might look like this:
http://example.com/tilestache.cgi/example-name/0/0/0.png
Sample JPEG creation options:
{
"quality": 90,
"progressive": true,
"optimize": true
}
Sample PNG creation options:
{
"optimize": true,
"palette": "filename.act"
}
Sample bounds:
{
"low": 9, "high": 15,
"south": 37.749, "west": -122.358,
"north": 37.860, "east": -122.113
}
Metatile represents a larger area to be rendered at one time. Metatiles are
represented in the configuration file as a dictionary:
{
"rows": 4,
"columns": 4,
"buffer": 64
}
- "rows" and "columns" are the height and width of the metatile measured in
tiles. This example metatile is four rows tall and four columns wide, so it
will render sixteen tiles simultaneously.
- "buffer" is a buffer area around the metatile, measured in pixels. This is
useful for providers with labels or icons, where it's necessary to draw a
bit extra around the edges to ensure that text is not cut off. This example
metatile has a buffer of 64 pixels, so the resulting metatile will be 1152
pixels square: 4 rows x 256 pixels + 2 x 64 pixel buffer.
The preview can be accessed through a URL like /<layer name>/preview.html:
{
"lat": 33.9901,
"lon": -116.1637,
"zoom": 16,
"ext": "jpg"
}
- "lat" and "lon" are the starting latitude and longitude in degrees.
- "zoom" is the starting zoom level.
- "ext" is the filename extension, e.g. "png".
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