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mkgmap-splitter - tile splitter for mkgmap


mkgmap-splitter [options] file.osm > splitter.log


mkgmap-splitter splits an .osm file that contains large well mapped regions into a number
of smaller tiles, to fit within the maximum size used for the Garmin maps format. There
are at least two stages of processing required. The first stage is to calculate what area
each tile should cover, based on the distribution of nodes. The second stage writes out
the nodes, ways and relations from the original .osm file into separate smaller .osm
files, one for each area that was calculated in stage one. With option
--keep-complete=true, two additional stages are used to avoid broken ways and polygons.

The two most important features are:

· Variable sized tiles to prevent a large number of tiny files.

· Tiles join exactly with no overlap or gaps.

You will need a lot of memory on your computer if you intend to split a large area. A few
options allow configuring how much memory you need. With the default parameters, you need
about 4-5 bytes for every node and way. This doesn't sound a lot but there are about 1700
million nodes in the whole planet file and so you cannot process the whole planet in one
pass file on a 32 bit machine using this utility as the maximum java heap space is 2G. It
is possible with 64 bit java and about 7GB of heap or with multiple passes.

The Europe extract from Cloudmade or Geofabrik can be processed within the 2G limit if you
have sufficient memory. With the default options europe is split into about 750 tiles.
The Europe extract is about half of the size of the complete planet file.

On the other hand a single country, even a well mapped one such as Germany or the UK, will
be possible on a modest machine, even a netbook.


Splitter requires java 1.6 or higher. Basic usage is as follows.

mkgmap-splitter file.osm > splitter.log

If you have less than 2 GB of memory on your computer you should reduce the -Xmx option by
setting the JAVA_OPTS environment variable.

JAVA_OPTS="-Xmx512m" mkgmap-splitter file.osm > splitter.log

This will produce a number of .osm.pbf files that can be read by mkgmap(1). There are
also other files produced:

The template.args file is a file that can be used with the -c option of mkgmap that will
compile all the files. You can use it as is or you can copy it and edit it to include
your own options. For example instead of each description being "OSM Map" it could be "NW
Scotland" as appropriate.

The areas.list file is the list of bounding boxes that were calculated. If you want you
can use this on a subsequent call the the splitter using the --split-file option to use
exactly the same areas as last time. This might be useful if you produce a map regularly
and want to keep the tile areas the same from month to month. It is also useful to avoid
the time it takes to regenerate the file each time (currently about a third of the overall
time taken to perform the split). Of course if the map grows enough that one of the tiles
overflows you will have to re-calculate the areas again.

The areas.poly file contains the bounding polygon of the calculated areas. See option
--polygon-file how this can be used.

The densities-out.txt file is written when no split-file is given and contains debugging
information only.

You can also use a gzip'ed or bz2'ed compressed .osm file as the input file. Note that
this can slow down the splitter considerably (particularly true for bz2) because
decompressing the .osm file can take quite a lot of CPU power. If you are likely to be
processing a file several times you're probably better off converting the file to one of
the binary formats pbf or o5m. The o5m format is faster to read, but requires more space
on the disk.


There are a number of options to fine tune things that you might want to try.

A comma separated list of tag values for relations. Used to filter multipolygon
and boundary relations for problem-list processing. See also option
--wanted-admin-level. Default: use-exclude-list

Deprecated, now does nothing

Sets the desciption to be written in to the template.args file.

The name of a GeoNames file to use for determining tile names. Typically
cities15000.zip from geonames ⟨http://download.geonames.org/export/dump⟩ .

Use --keep-complete=false to disable two additional program phases between the
split and the final distribution phase (not recommended). The first phase, called
gen-problem-list, detects all ways and relations that are crossing the borders of
one or more output files. The second phase, called handle-problem-list, collects
the coordinates of these ways and relations and calculates all output files that
are crossed or enclosed. The information is passed to the final dist-phase in
three temporary files. This avoids broken polygons, but be aware that it requires
to read the input files at least two additional times.

Do not specify it with --overlap unless you have a good reason to do so.

Defaulte: true

Set the filename for the split files. In the example the first file will be called
63240001.osm.pbf and the next one will be 63240002.osm.pbf and so on.

Default: 63240001

The maximum number of areas that can be processed in a single pass during the
second stage of processing. This must be a number from 1 to 4096. Higher numbers
mean fewer passes over the source file and hence quicker overall processing, but
also require more memory. If you find you are running out of memory but don't want
to increase your --max-nodes value, try reducing this instead. Changing this will
have no effect on the result of the split, it's purely to let you trade off memory
for performance. Note that the first stage of the processing has a fixed memory
overhead regardless of what this is set to so if you are running out of memory
before the areas.list file is generated, you need to either increase your -Xmx
value or reduce the size of the input file you're trying to split.

Default: 512

The maximum number of nodes that can be in any of the resultant files. The default
is fairly conservative, you could increase it quite a lot before getting any 'map
too big' messages. Not much experimentation has been done. Also the bigger this
value, the less memory is required during the splitting stage.

Default: 1600000

The maximum number of threads used by mkgmap-splitter.

Default: 4 (auto)

Specify this if the input osm file has nodes, ways and relations intermingled or
the ids are not strictly sorted. To increase performance, use the osmosis sort

Default: false

Don't trim empty space off the edges of tiles. This option is ignored when
--polygon-file is used.

Default: false

A target value that is used when no split-file is given. Splitting is done so that
the given number of tiles is produced. The --max-nodes value is ignored if this
option is given.

The format in which the output files are written. Possible values are xml, pbf,
o5m, and simulate. The default is pbf, which produces the smallest file sizes.
The o5m format is faster to write, but creates around 40% larger files. The
simulate option is for debugging purposes.

The directory to which splitter should write the output files. If the specified
path to a directory doesn't exist, mkgmap-splitter tries to create it. Defaults to
the current working directory.

Deprecated since r279. With --keep-complete=false, mkgmap-splitter should include
nodes outside the bounding box, so that mkgmap can neatly crop exactly at the
border. This parameter controls the size of that overlap. It is in map units, a
default of 2000 is used which means about 0.04 degrees of latitude or longitude.
If --keep-complete=true is active and --overlap is given, a warning will be printed
because this combination rarely makes sense.

An osm file (.o5m, .pbf, .osm) with named ways that describe bounding polygons with
OSM ways having tags name and mapid.

The name of a file containing a bounding polygon in the osmosis polygon file format
. mkgmap-splitter uses this file when calculating the areas. It first calculates
a grid using the given --resolution. The input file is read and for each node, a
counter is increased for the related grid area. If the input file contains a
bounding box, this is applied to the grid so that nodes outside of the bounding box
are ignored. Next, if specified, the bounding polygon is used to zero those grid
elements outside of the bounding polygon area. If the polygon area(s) describe(s)
a rectilinear area with no more than 40 vertices, mkgmap-splitter will try to
create output files that fit exactly into the area, otherwise it will approximate
the polygon area with rectangles.

The name of a directory containing precompiled sea tiles. If given, mkgmap-
splitter will use the precompiled sea tiles in the same way as mkgmap does. Use
this if you want to use a polygon-file or --no-trim=true and mkgmap creates empty
*.img files combined with a message starting "There is not enough room in a single
garmin map for all the input data".

The name of a file containing ways and relations that are known to cause problems
in the split process. Use this option if --keep-complete requires too much time or
memory and --overlap doesn't solve your problem.

Syntax of problem file:

way:<id> # comment...
rel:<id> # comment...


way:2784765 # Ferry Guernsey - Jersey

The name of a file to write the generated problem list created with
--keep-complete. The parameter is ignored if --keep-complete=false. You can reuse
this file with the --problem-file parameter, but do this only if you use the same
values for --max-nodes and --resolution.

The resolution of the density map produced during the first phase. A value between
1 and 24. Default is 13. Increasing the value to 14 requires four times more
memory in the split phase. The value is ignored if a --split-file is given.

Search limit in split algo. Higher values may find better splits, but will take

Default: 200000

Use the previously calculated tile areas instead of calculating them from scratch.
The file can be in .list or .kml format.

Displays the amount of memory used by the JVM every --status-freq seconds. Set =0
to disable.

Default: 120

Debugging: stop after a given program phase. Can be split, gen-problem-list, or
handle-problem-list. Default is dist which means execute all phases.

Specifies the lowest admin_level value of boundary relations that should be kept
complete. Used to filter boundary relations for problem-list processing. The
default value 5 means that boundary relations are kept complete when the
admin_level is 5 or higher (5..11). The parameter is ignored if
--keep-complete=false. Default: 5

The name of a kml file to write out the areas to. This is in addition to
areas.list (which is always written out).

Special options

If the parameter --version is found somewhere in the options, mkgmap-splitter will
just print the version info and exit. Version info looks like this:

splitter 279 compiled 2013-01-12T01:45:02+0000

--help If the parameter --help is found somewhere in the options, mkgmap-splitter will
print a list of all known normal options together with a short help and exit.


Tuning for best performance

A few hints for those that are using mkgmap-splitter to split large files.

· For faster processing with --keep-complete=true, convert the input file to o5m format

osmconvert --drop-version file.osm -o=file.o5m

· The option --drop-version is optional, it reduces the file to that data that is needed
by mkgmap-splitter and mkgmap.

· If you still experience poor performance, look into splitter.log. Search for the word
Distributing. You may find something like this in the next line:

Processing 1502 areas in 3 passes, 501 areas at a time

This means splitter has to read the input file input three times because the --max-areas
parameter was much smaller than the number of areas. If you have enough heap, set
--max-areas value to a value that is higher than the number of areas, e.g.
--max-areas=2048. Execute mkgmap-splitter again and you should find

Processing 1502 areas in a single pass

· More areas require more memory. Make sure that mkgmap-splitter has enough heap
(increase the -Xmx parameter) so that it doesn't waste much time in the garbage
collector (GC), but keep as much memory as possible for the systems I/O caches.

· If available, use two different disks for input file and output directory, esp. when you
use o5m format for input and output.

· If you use mkgmap r2415 or later and disk space is no concern, consider to use
--output=o5m to speed up processing.

Tuning for low memory requirements

If your machine has less than 1 GB free memory (eg. a netbook), you can still use mkgmap-
splitter, but you might have to be patient if you use the parameter --keep-complete and
want to split a file like germany.osm.pbf or a larger one. If needed, reduce the number
of parrallel processed areas to 50 with the --max-areas parameter. You have to use
--keep-complete=false when splitting an area like Europe.


· There is no longer an upper limit on the number of areas that can be output (previously
it was 255). More areas just mean potentially more passes being required over the .osm
file, and hence the splitter will take longer to run.

· There is no longer a limit on how many areas a way or relation can belong to (previously
it was 4).

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