maplayer.py

#

from layersource import handle_layer_source
from filter import filter_record


_verbose = False

#

MapLayer

Represents a layer in the map which contains a list of map features

class MapLayer(object):

#

    def __init__(self, id, options, _map, cache):

#

Store layer properties as instance properties

        self.id = id
        self.options = options
        self.map = _map
        self.cache = cache

#

Make sure that the layer id is unique within the map.

        while self.id in self.map.layersById:
            self.id += "_"

#

Instantiate the layer source which will generate features from the source geo data such as shapefiles or virtual sources such as graticule lines.

        self.source = handle_layer_source(self.options, self.cache)

#

get_features()

Returns a list of projected and filtered features of a layer.

    def get_features(layer, filter=False, min_area=0):

#

        opts = layer.map.options
        is_projected = False

#

Let's see if theres a better bounding box than this..

        bbox = [-180, -90, 180, 90]

#

Use the clipping mode defined in the map configuration

        if opts['bounds']['mode'] == "bbox":
            bbox = opts['bounds']['data']

#

The 'crop' property overrides the clipping settings

        if 'crop' in opts['bounds'] and opts['bounds']['crop']:

#

If crop is set to "auto", which is the default behaviour, Kartograph will use the actual bounding geometry to compute the bounding box

            if opts['bounds']['crop'] == "auto":
                if layer.map._unprojected_bounds:
                    bbox = layer.map._unprojected_bounds
                    bbox.inflate(inflate=opts['bounds']['padding'] * 2)
                else:
                    print 'could not compute bounding box for auto-cropping'
            else:

#

otherwise it will use the user defined bbox in the format [minLon, minLat, maxLon, maxLat]

                bbox = opts['bounds']['crop']

#

If the layer has the "src" property, it is a regular map layer source, which means that there's an exernal file that we load the geometry and meta data from.

        if 'src' in layer.options:
            if layer.options['filter'] is False:
                filter = None
            else:
                filter = lambda rec: filter_record(layer.options['filter'], rec)

#

Now we ask the layer source to generate the features that will be displayed in the map.

            features = layer.source.get_features(
                filter=filter,
                bbox=bbox,
                ignore_holes='ignore-holes' in layer.options and layer.options['ignore-holes'],
                charset=layer.options['charset']
            )
            if _verbose:
                print 'loaded %d features from shapefile %s' % (len(features), layer.options['src'])

#

In contrast to regular layers, the geometry for special (or virtual) layers is generated by Kartograph itself, based on some properties defined in the layer config.

        elif 'special' in layer.options:

#

The graticule layer generates line features for longitudes and latitudes

            if layer.options['special'] == "graticule":
                lats = layer.options['latitudes']
                lons = layer.options['longitudes']
                features = layer.source.get_features(lats, lons, layer.map.proj, bbox=bbox)

#

The "sea" layer generates a MultiPolygon that represents the entire boundary of the map. Especially useful for non-cylindrical map projections.

            elif layer.options['special'] == "sea":
                features = layer.source.get_features(layer.map.proj)
                is_projected = True

        for feature in features:

#

If the features are not projected yet, we project them now.

            if not is_projected:
                feature.project(layer.map.proj)

#

Transform features to view coordinates.

            feature.project_view(layer.map.view)

#

Remove features that don't intersect our clipping polygon

        if layer.map.view_poly:
            features = [feature for feature in features
            if feature.geometry and feature.geometry.intersects(layer.map.view_poly)]
        layer.features = features