TileStache.Core module

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”: ..., “redirects”: ..., “tile height”: ..., “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.

  • “tile height” gives the height of the image tile in pixels. You almost always want to leave this at the default value of 256, but you can use a value of 512 to create double-size, double-resolution tiles for high-density phone screens.

  • “jpeg options” is an optional dictionary of JPEG creation options, passed through to PIL: http://effbot.org/imagingbook/format-jpeg.htm.

  • “png options” is an optional dictionary of PNG creation options, passed through to PIL: http://effbot.org/imagingbook/format-png.htm.

  • “pixel effect” is an optional dictionary that defines an effect to be applied

    for all tiles of this layer. Pixel effect can be any of these: blackwhite,

    greyscale, desaturate, pixelate, halftone, or blur.

The public-facing URL of a single tile for this layer might look like this:

Sample JPEG creation options:

{
“quality”: 90, “progressive”: true, “optimize”: true

}

Sample PNG creation options:

{
“optimize”: true, “palette”: “filename.act”

}

Sample pixel effect:

{
“name”: “desaturate”, “factor”: 0.85

}

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”.
exception TileStache.Core.KnownUnknown

Bases: exceptions.Exception

There are known unknowns. That is to say, there are things that we now know we don’t know.

This exception gets thrown in a couple places where common mistakes are made.

class TileStache.Core.Layer(config, projection, metatile, stale_lock_timeout=15, cache_lifespan=None, write_cache=True, allowed_origin=None, max_cache_age=None, redirects=None, preview_lat=37.8, preview_lon=-122.26, preview_zoom=10, preview_ext='png', bounds=None, tile_height=256)

A Layer.

Required attributes:

provider:
Render provider, see Providers module.
config:
Configuration instance, see Config module.
projection:
Geographic projection, see Geography module.
metatile:
Some information for drawing many tiles at once.

Optional attributes:

stale_lock_timeout:
Number of seconds until a cache lock is forced, default 15.
cache_lifespan:
Number of seconds that cached tiles should be stored, default 15.
write_cache:
Allow skipping cache write altogether, default true.
bounds:
Instance of Config.Bounds for limiting rendered tiles.
allowed_origin:
Value for the Access-Control-Allow-Origin HTTP response header.
max_cache_age:
Number of seconds that tiles from this layer may be cached by downstream clients.
redirects:
Dictionary of per-extension HTTP redirects, treated as lowercase.
preview_lat:
Starting latitude for slippy map layer preview, default 37.80.
preview_lon:
Starting longitude for slippy map layer preview, default -122.26.
preview_zoom:
Starting zoom for slippy map layer preview, default 10.
preview_ext:
Tile name extension for slippy map layer preview, default “png”.
tile_height:
Height of tile in pixels, as a single integer. Tiles are generally assumed to be square, and Layer.render() will respond with an error if the rendered image is not this height.
doMetatile()

Return True if we have a real metatile and the provider is OK with it.

envelope(coord)

Projected rendering envelope (xmin, ymin, xmax, ymax) for a Coordinate.

getTileResponse(coord, extension, ignore_cached=False)

Get status code, headers, and a tile binary for a given request layer tile.

Arguments: - coord: one ModestMaps.Core.Coordinate corresponding to a single tile. - extension: filename extension to choose response type, e.g. “png” or “jpg”. - ignore_cached: always re-render the tile, whether it’s in the cache or not.

This is the main entry point, after site configuration has been loaded and individual tiles need to be rendered.

getTypeByExtension(extension)

Get mime-type and PIL format by file extension.

metaEnvelope(coord)

Projected rendering envelope (xmin, ymin, xmax, ymax) for a metatile.

metaSize(coord)

Pixel width and height of full rendered image for a metatile.

metaSubtiles(coord)

List of all coords in a metatile and their x, y offsets in a parent image.

name()

Figure out what I’m called, return a name if there is one.

Layer names are stored in the Configuration object, so config.layers must be inspected to find a matching name.

render(coord, format)

Render a tile for a coordinate, return PIL Image-like object.

Perform metatile slicing here as well, if required, writing the full set of rendered tiles to cache as we go.

Note that metatiling and pass-through mode of a Provider are mutually exclusive options

setSaveOptionsJPEG(quality=None, optimize=None, progressive=None)

Optional arguments are added to self.jpeg_options for pickup when saving.

More information about options:
http://effbot.org/imagingbook/format-jpeg.htm
setSaveOptionsPNG(optimize=None, palette=None, palette256=None)

Optional arguments are added to self.png_options for pickup when saving.

Palette argument is a URL relative to the configuration file, and it implies bits and optional transparency options.

More information about options:
http://effbot.org/imagingbook/format-png.htm
class TileStache.Core.Metatile(buffer=0, rows=1, columns=1)

Some basic characteristics of a metatile.

Properties: - rows: number of tile rows this metatile covers vertically. - columns: number of tile columns this metatile covers horizontally. - buffer: pixel width of outer edge.

allCoords(coord)

Return a list of coordinates for a complete metatile.

Results are guaranteed to be ordered left-to-right, top-to-bottom.

firstCoord(coord)

Return a new coordinate for the upper-left corner of a metatile.

This is useful as a predictable way to refer to an entire metatile by one of its sub-tiles, currently needed to do locking correctly.

isForReal()

Return True if this is really a metatile with a buffer or multiple tiles.

A default 1x1 metatile with buffer=0 is not for real.

exception TileStache.Core.NoTileLeftBehind(tile)

Bases: exceptions.Exception

Leave no tile in the cache.

This exception can be thrown in a provider to signal to TileStache.getTile() that the result tile should be returned, but not saved in a cache. Useful in cases where a full tileset is being rendered for static hosting, and you don’t want millions of identical ocean tiles.

The one constructor argument is an instance of PIL.Image or some other object with a save() method, as would be returned by provider renderArea() or renderTile() methods.

exception TileStache.Core.TheTileLeftANote(headers=None, status_code=200, content='', emit_content_type=True)

Bases: exceptions.Exception

A tile exists, but it shouldn’t be returned to the client. Headers and/or a status code are provided in its stead.

This exception can be thrown in a provider or a cache to signal to upstream servers where a tile can be found or to clients that a tile is empty (or solid).

TileStache.Core.loadClassPath(classpath)

Load external class based on a path.

Example classpath: “Module.Submodule:Classname”.

Equivalent soon-to-be-deprecated classpath: “Module.Submodule.Classname”.