OSM Map On Garmin/NOD Subfile Format

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OSM Map On Garmin

A reverse-engineering of Garmin's NOD Subfile format

Header

NOD Header

Common Header

The structure of the common header is the same in all subfiles.

Byte Offset Length (bytes) Description
0x000 2 Header length. So far '0x3f' and '0x7f' have been seen.
0x002 10 Type GARMIN NOD
0x00C 1 0x01 ?
0x00D 1 0x00
0x00E 2 Creation year
0x010 1 Creation month
0x011 1 Creation day
0x012 1 Creation hour
0x013 1 Creation minute
0x014 1 Creation second

Specific NOD Header

Byte Offset Length (bytes) Description
0x015 4 NOD1 section offset
0x019 4 NOD1 section length
0x01D 1 Unknown. Lower bit always set. 0x01 and 0x27 spotted
0x01E 1 Flag: 0x01: left-hand drive. others unknown (0x02 spotted)
0x01F 2 Unknown. 0x0000
0x021 2 Unknown. 0x06
0x023 2 Unknown. 0x05
0x025 4 NOD2 section offset
0x029 4 NOD2 section length
0x02D 4 Unknown 0x0000
0x031 4 NOD3 section offset
0x035 4 NOD3 section length
0x039 1 NOD3 section record length. 0x09
0x03a 4 Unknown 0x00 and 0x0200 spotted
0x03e 1 Unknown 0x00
0x03f 4 NOD4 section offset
0x043 4 NOD4 section length
0x047 32 Unknown all bytes 0x00
0x067 4 NOD5 section offset
0x06b 4 NOD5 section length
0x06f 2 Unknown 0x02 spotted
0x071 4 NOD6 section offset
0x075 4 NOD6 section length
0x079 2 NOD6 record size
0x07b 4 Unknown 0x02 spotted

NOD1 section

This consists of alternating nodes and tables areas.

The nodes area consists of variable sized records. Each record is as follows:

Node header

Node record begins with a header:

Byte Offset Length (bytes) Description
0x00 1 Pointer to table area. Associated table area is at pointer * 0x40
0x01 1 Flags: 0x04: unknown, usually set; 0x08: boundary node; 0x10:restrictions; 0x20: 2 byte coordinate offsets; 0x40: has arcs
0x02 varies Coordinate offsets. If flag 0x20 is unset this is 3 bytes (12 bits for each offset) else this is 4 bytes (16 bits for each offset)

Links

Directly following node header is a sequence of links:

Byte Offset Length (bytes) Description
0x00 1 Flags A: bits 0-2: destination class; 3-5: curve length; 6: sign; 7: new direction
0x01 1 or 2 Flags B: 0x40: inter-area link; 0x80: last node / pointer index B (see [1])
variable 1 pointer index A
variable 1 to 3 first is direction?

The tablesarea consists of a header and three tables:

Tables header

Byte Offset Length (bytes) Description
0x00 1 0-1: size of Table C size field; 2-7: unknown (???? this is not correct see Explore IMG)
0x01 3 base longitude
0x04 3 base latitude
0x07 1 number of records in table A
0x08 1 number of records in table B

Table A

Table A contains fixed length records of 5 bytes representing road segments.

Byte Offset Length (bytes) Description
0x00 3 0-29: Pointer to NET; 30: no delivery; 31: no emergency
0x03 1 class flag: 0-3: road speed; 4: oneway; 5-6: road class; 8: toll
0x04 1 access flag: 0: no car; 1: no bus; 2: no taxi; 3: no through routing; 4: no foot; 5: no bike; 6: no truck; 7: carpool only (<-- ??? ) - looks like Road ID!

Table B

Table B contains fixed length records of 3 bytes representing destinations of inter area links.

Table C

If size of Table C size field was zero, table B is followed by 2 optional bytes indicating respectively the number of unpaved arcs and ferry arcs in table A, then 0x00.

Else there is size of Table C size field bytes indicating the length of table C. Following this are restriction records:

Byte Offset Length (bytes) Description
0x00 1 unknown; 0x05 spotted
0x01 1 Flag: 0: unknown; 1: pedestrian exception; 2: emergency exception; 3: additional vehicle exceptions; 4: unknown; 5-7: number of ways
0x02 1 unknown; 0x00 spotted
0x03 1 Optional (present if vehicle additional exceptions is active in header flag). Vehicle exceptions flag: 0x01: car; 0x02: bus; 0x04: taxi; 0x10: delivery; 0x20: bicycle; 0x40: truck
variable, repeated nb_ways+1 times 2 node
variable, repeated nb_ways times 1 segment

Finally the table is finished by 2 optional bytes indicating respectively the number of unpaved arcs and ferry arcs in table A.

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