Processing Digital Maps - Programming GPS and OpenStreetMap Applications with Java - page 89

Coverage Zipped Unzipped Ratio Unzip Rezip Ratio

Germany 1,207 MB 14,875 MB 8% 2 h 30 min 5 h 09 min 200%

RGB-NW 480 KB

5,950 MB 8% 5 min 10 min 200%

Table7.2. Uncompressing and recompressing OSM deliveries. (Hardware: dual
core CPU 1.67 GHz, 4 GB RAM, Win32 OS.)

to the source. When using different tools (or even one tool) unzipping and
rezipping a file most likely does not produce the identical byte size.
The benchmarks for the Germany map indicate that it takes almost four
hours to download the map and unpack it. For the single RGB-NW project
this is a lot of pre-processing. In a larger context, it might be worthwhile
to download and uncompress an entire continent for a whole day in order
to clip a few hundred bounding boxes all over Europe for one application
in different locations.

Clipping Maps

Compressing is not really a map-related process and does not require os-
mosis. Vice versa, osmosis can execute map-related functions on packed
OSM data. Earlier JOSM was used to download and save a bounding box
directly with the front-end tool. With osmosis, another approach can be
chosen to get the same map area. With the command line options below,
the RGB-NW area can be clipped directly from the packed Germany map.

--rx germany.osm.bz2
--bb left="11.95" right="12.10" top="49.10" bottom="49.02"
--wx RGB-NW.osm.bz2

By unpacking it (see Table 7.2), the file should nearly match the file
saved directly from JOSM on page 83.
With the command line options, the RGB-NW area can be clipped directly
from the unpacked Germany map.

--rx germany.osm
--bb left="11.95" right="12.10" top="49.10" bottom="49.02"
--wx RGB-NW.osm

So there are different ways to get to the RGB-NW.osm file:

germany.osm.bz2 - 2h 30 - germany.osm
| |

20
| |
RGB-NW.osm.bz2 - 5 sec - RGB-NW.osm

2h 05