mirror of
https://github.com/protomaps/PMTiles.git
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70 lines
2.2 KiB
Python
70 lines
2.2 KiB
Python
import json
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import mmap
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from contextlib import contextmanager
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@contextmanager
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def read(fname):
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r = Reader(fname)
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try:
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yield r
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finally:
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r.close()
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class Reader:
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def __init__(self,fname):
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self.f = open(fname, "r+b")
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self.mmap = mmap.mmap(self.f.fileno(), 0)
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assert int.from_bytes(self.mmap[0:2],byteorder='little') == 0x4D50
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first_entry_idx = 10+self.metadata_len
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self.root_dir, self.leaves = self.load_directory(first_entry_idx,self.root_entries)
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def load_directory(self,offset,num_entries):
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directory = {}
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leaves = {}
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for i in range(offset,offset+num_entries*17,17):
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z = int.from_bytes(self.mmap[i:i+1],byteorder='little')
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x = int.from_bytes(self.mmap[i+1:i+4],byteorder='little')
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y = int.from_bytes(self.mmap[i+4:i+7],byteorder='little')
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tile_off = int.from_bytes(self.mmap[i+7:i+13],byteorder='little')
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tile_len = int.from_bytes(self.mmap[i+13:i+17],byteorder='little')
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if (z & 0b10000000):
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leaves[(z & 0b01111111,x,y)] = (tile_off,tile_len)
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else:
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directory[(z,x,y)] = (tile_off,tile_len)
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return (directory,leaves)
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def close(self):
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self.f.close()
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@property
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def metadata_len(self):
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return int.from_bytes(self.mmap[4:8],byteorder='little')
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@property
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def metadata(self):
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s = self.mmap[10:10+self.metadata_len]
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return json.loads(s)
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@property
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def version(self):
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return int.from_bytes(self.mmap[2:4],byteorder='little')
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@property
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def root_entries(self):
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return int.from_bytes(self.mmap[8:10],byteorder='little')
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def get(self,z,x,y):
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val = self.root_dir.get((z,x,y))
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if val:
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return self.mmap[val[0]:val[0]+val[1]]
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else:
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z7_tile_diff = z - 7
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z7_tile = (7,x // (1 << z7_tile_diff),y // (1 << z7_tile_diff))
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val = self.leaves.get(z7_tile)
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if val:
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directory, _ = self.load_directory(val[0],val[1]//17)
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val = directory.get((z,x,y))
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if val:
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return self.mmap[val[0]:val[0]+val[1]]
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