def render_png(tile, zoom, xml, overscan):
map_tile_size = TILE_SIZE + (overscan * 2)
# mapnik is installed in a non-standard way.
# It confuses pylint.
# pylint: disable=no-member
"""
Render the tile for the given zoom
"""
logger = get_logger()
ctx = mapnik.Context()
map_tile = mapnik.Map(map_tile_size, map_tile_size)
# scale_denom = 1 << (BASE_ZOOM - int(zoom or 1))
# scale_factor = scale_denom / map_tile.scale_denominator()
# map_tile.zoom(scale_factor) # Is overriden by zoom_to_box.
mapnik.load_map_from_string(map_tile, xml)
box_min = -overscan
box_max = TILE_SIZE + overscan - 1
map_tile.zoom_to_box(mapnik.Box2d(box_min, box_min, box_max, box_max))
for (name, features) in tile.items():
name = name.encode('ascii', 'ignore')
source = mapnik.MemoryDatasource()
map_layer = mapnik.Layer(name)
map_layer.datasource = source
for feature in features:
feat = mapnik.Feature(ctx, 0)
try:
feat.add_geometries_from_wkb(feature)
except RuntimeError:
from mapnik import Path # pylint: disable=no-name-in-module
try:
wkt = Path.from_wkb(feature).to_wkt()
logger.error('Invalid feature: %s', wkt)
except RuntimeError:
logger.error('Corrupt feature: %s', feature.encode('hex'))
source.add_feature(feat)
map_layer.styles.append(name)
map_tile.layers.append(map_layer)
image = mapnik.Image(TILE_SIZE, TILE_SIZE)
# tile, image, scale, offset_x, offset_y
mapnik.render(map_tile, image, 1, overscan, overscan)
return image.tostring('png')
def to_wkb(*wkts):
from mapnik import Path, wkbByteOrder # pylint: disable=no-name-in-module
return [Path.from_wkt(wkt).to_wkb(wkbByteOrder.XDR) for wkt in wkts]
