Hello,
While trying to decode PBF files with a Perl script, I encounter problems with
the OSMHeader fileblock. The content of the uncompressed content of the block is:
0a 1a 08 fe e3 86 8a 47 10 80 ae e9 da 4d 18 80 9c f8 eb ea 02 20 80 88 8d 8f e7
02 22 0e 4f 73 6d 53 63 68 65 6d 61 2d 56 30 2e 36 22 0a 44 65 6e 73 65 4e 6f 64
65 73 82 01 04 30 2e 33 38 8a 01 24 68 74 74 70 3a 2f 2f 77 77 77 2e 6f 70 65 6e
73 74 72 65 65 74 6d 61 70 2e 6f 72 67 2f 61 70 69 2f 30 2e 36 00
According to the specification at http://wiki.openstreetmap.org/wiki/PBF_Format
the structure of the block is:
message HeaderBlock {
optional HeaderBBox bbox = 1;
/* Additional tags to aid in parsing this dataset */
repeated string required_features = 4;
repeated string optional_features = 5;
optional string writingprogram = 16;
optional string source = 17; // From the bbox field.
}
With the above data, this results in:
key: 0a -> type=length-delimited field_number=1 -> Headerbox bbox
length: 26
value: 08 fe e3 86 8a 47 10 80 ae e9 da 4d 18 80 9c f8 eb ea 02 20 80 88 8d 8f
e7 02
key: 22 -> type=length-delimited field_number=4 -> string required_features
length: 14
value: 4f 73 6d 53 63 68 65 6d 61 2d 56 30 2e 36 "OsmSchema-V0.6"
key: 22 -> type=length-delimited field_number=4 -> string required_features
length: 10
value: 44 65 6e 73 65 4e 6f 64 65 73 "DenseNodes"
key: 82 -> type=length-delimited field_number=16 -> string writingprogram
Next should follow the field length of the length-delimited string as a varint
encoded integer, followed by the specified number of characters. However, there is:
01 04 30 2e 33 38 8a
which would be fine *without* the leading 0x01:
length: 4
value: 30 2e 33 38 8a "0.38"
What is this extra 01 at the beginning of the data length, a misunderstanding on
my side, a problem in the doc or a bug?
Rainer
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