def buffer_extent(extent, zoom_level, num_tiles=6, tile_size=256, units='degrees'):
"""
Buffers an extent by the size of num_tiles at a particular zoom level.
"""
scale = settings.MAP_SCALES[zoom_level]
resolution = get_resolution(scale, units)
ll_px = px_from_lnglat((extent[0], extent[1]), resolution)
ur_px = px_from_lnglat((extent[2], extent[3]), resolution)
pixel_buf = num_tiles * tile_size
# Note that the (0, 0) point for the lnglat_from_px function is upper-left,
# so /addition/ of the buffer to the y component moves it in the negative
# direction, and vice versa
ll_px = (ll_px[0] - pixel_buf, ll_px[1] + pixel_buf)
ur_px = (ur_px[0] + pixel_buf, ur_px[1] - pixel_buf)
return lnglat_from_px(ll_px, resolution) + lnglat_from_px(ur_px, resolution)
def cluster_by_scale(objs,
radius,
scale,
extent=(-180, -90, 180, 90),
cluster_fn=cluster.buffer_cluster):
"""
Required parameters:
+ objs: dict, keys to ID objects, values are point 2-tuples
+ radius: in pixels
+ scale: 'n' in '1/n', eg., 19200
"""
resolution = get_resolution(scale)
# Translate from lng/lat into coordinate system of the display.
objs = dict([(k, px_from_lnglat(v, resolution, extent))
for k, v in objs.iteritems()])
bunches = []
for bunch in cluster_fn(objs, radius):
# Translate back into lng/lat.
bunch.center = lnglat_from_px(bunch.center, resolution, extent)
bunches.append(bunch)
return bunches
def buffer_extent(extent,
zoom_level,
num_tiles=6,
tile_size=256,
units='degrees'):
"""
Buffers an extent by the size of num_tiles at a particular zoom level.
"""
scale = settings.MAP_SCALES[zoom_level]
resolution = get_resolution(scale, units)
ll_px = px_from_lnglat((extent[0], extent[1]), resolution)
ur_px = px_from_lnglat((extent[2], extent[3]), resolution)
pixel_buf = num_tiles * tile_size
# Note that the (0, 0) point for the lnglat_from_px function is upper-left,
# so /addition/ of the buffer to the y component moves it in the negative
# direction, and vice versa
ll_px = (ll_px[0] - pixel_buf, ll_px[1] + pixel_buf)
ur_px = (ur_px[0] + pixel_buf, ur_px[1] - pixel_buf)
return lnglat_from_px(ll_px, resolution) + lnglat_from_px(
ur_px, resolution)
def cluster_by_scale(objs, radius, scale, extent=(-180, -90, 180, 90),
cluster_fn=cluster.buffer_cluster):
"""
Required parameters:
+ objs: dict, keys to ID objects, values are point 2-tuples
+ radius: in pixels
+ scale: 'n' in '1/n', eg., 19200
"""
resolution = get_resolution(scale)
# Translate from lng/lat into coordinate system of the display.
objs = dict([(k, px_from_lnglat(v, resolution, extent)) for k, v in objs.iteritems()])
bunches = []
for bunch in cluster_fn(objs, radius):
# Translate back into lng/lat.
bunch.center = lnglat_from_px(bunch.center, resolution, extent)
bunches.append(bunch)
return bunches