Processing Digital Maps - Programming GPS and OpenStreetMap Applications with Java - page 82

out the map image), you can watch the map drawing itself. The availability
of GPS devices allows anyone to collect map data at low cost and with high
accuracy. Every navigation system and many smartphones collect data
all the time|and the manufactures know how to retrieve them. This is
changing the mapping business dramatically as it doesn't require geo- and
cartographic skills.
Commercial vendors of digital maps have large field teams all over the
globe, driving (tens of) thousands of kilometers every month to collect
every piece of information that might be of interest. Since every field trip
consumes manpower, time, and money, the field cars are equipped with
multiple sensors from differential GPS to video cameras. For best accuracy,
the measurements of the GPS are compared to the traveled distance of the
car and each change of heading is marked. Fieldwork has to consider the
difference of the distance traveled between left and right tires, tire pressure,
wheel slip, temperature, etc.
Due to different time zones and many other factors, it makes sense to
always have the map available online for the field team. Map engineers can
check-out (download) any part of the map, edit it, and finally check it back
in (upload). Large teams have to be synchronized, concurrent editing has
to be reintegrated, and precise timing schedules exist, when a map is locked
and flushed to snapshots and extracted to different formats in consecutive
steps.
The geometry represents the fundamental grid for any map and the
majority of it needs to be collected only once. However, the collected traces
can not be integrated directly into a map. Besides deviating slightly from
the real road geometry, there are simply too many positions. The scenario
RGB-BUELL includes about 50 traces with about 40,000 points. Each trace
can be loaded and compared against the OpenStreetMap data with the
Java OpenStreetMap Editor (JOSM).
The Java OpenStreetMap editor. In order to get your own graphical map-
ping front end, please visit
josm.openstreetmap.de
and download the latest JOSM version 1 to the following directory:
../resources/OSM.compiler/tools/josm<version>
JOSM is a graphical front end to view digital maps in the OpenStreetMap
(XML) format and GPX traces. Once you have downloaded JOSM and
opened the editor, you can load the GPX files of the RGB-BUELL-NW scenario. 2
1 For this chapter version 3592 2010-10-05 was used.
2 Right click on the GPX layer and convert to data layer to see a consecutive trace.