TileStache.Geography module

The geography bits of TileStache.

A Projection defines the relationship between the rendered tiles and the underlying geographic data. Generally, just one popular projection is used for most web maps, “spherical mercator”.

Built-in projections: - spherical mercator - WGS84

Example use projection in a layer definition:

“layer-name”: {

“projection”: “spherical mercator”, ...

}

You can define your own projection, with a module and object name as arguments:

“layer-name”: {

... “projection”: “Module:Object”

}

The object must include methods that convert between coordinates, points, and locations. See the included mercator and WGS84 implementations for example. You can also instantiate a projection class using this syntax:

“layer-name”: {

... “projection”: “Module:Object()”

}

class TileStache.Geography.SphericalMercator

Bases: ModestMaps.Geo.MercatorProjection

Spherical mercator projection for most commonly-used web map tile scheme.

This projection is identified by the name “spherical mercator” in the TileStache config. The simplified projection used here is described in greater detail at: http://trac.openlayers.org/wiki/SphericalMercator

coordinateProj(coord)

Convert from Coordinate object to a Point object in EPSG:900913

locationProj(location)

Convert from Location object to a Point object in EPSG:900913

projCoordinate(point)

Convert from Point object in EPSG:900913 to a Coordinate object

projLocation(point)

Convert from Point object in EPSG:900913 to a Location object

srs = '+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs +over'

class TileStache.Geography.WGS84

Bases: ModestMaps.Geo.LinearProjection

Unprojected projection for the other commonly-used web map tile scheme.

This projection is identified by the name “WGS84” in the TileStache config.

coordinateProj(coord)

Convert from Coordinate object to a Point object in EPSG:4326

locationProj(location)

Convert from Location object to a Point object in EPSG:4326

projCoordinate(point)

Convert from Point object in EPSG:4326 to a Coordinate object

projLocation(point)

Convert from Point object in EPSG:4326 to a Location object

srs = '+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs'

TileStache.Geography.getProjectionByName(name)

Retrieve a projection object by name.

Raise an exception if the name doesn’t work out.