Global Positioning System Reference
In-Depth Information
had few performance requirements, the new environment allows scaled per-
formance tests. Observe the GUI behavior with 20, 30, and 40 traces, while
constantly changing the window size, map position, etc.
The GUI developer can improve the map application by increasing the
number of traces, reducing the drawing on the visible part of the map, add
a preference pane as in the GPXviewer , etc.
Watching the bikes in the RGB-BUELL-NW scenario illustrates a number
of things: The GPS receiver collects reliable positions on the same (side
of the) road on different days. Not all, but most of the points line up to
a plausible trace. The implementations of Position and GPSpoint allow
a reconstruction and playback of the traces. The traces closely match the
roads on the map image and, with constant sample rate, the pixel distances
imply speed.
The map RGB-BUELL-NW.png of this scenario is sucient information for
anyone familiar with this area. Most of the traces are in the area bounded
by three rivers, covered with plenty of woodland, grass or fields (green),
downtown in the south is roughly depicted by a gray area and the train
track gives the image a signature. Most people know the shape of their
country or state (in a familiar projection) at first site. For another scenario,
this map may be completely useless. Images of maps or raster maps, are
composed of a fixed number of picture cells, pixels. These maps are totally
inflexible and although they can be scaled, as in the MapPanel , the details
do not change.
Where do these map images come from? The next chapter will guide
you through the creation of your own map for your geographical area and
purpose.
 
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