From Geography to Cartography - Programming GPS and OpenStreetMap Applications with Java - page 56

can be used to identify a point on the globe with (lat,lon) tuples|if the
corresponding ellipsoid-date model is known.
For any chosen model, JavaGPS can transform the coordinates to the
Gauss Kruger (GK) coordinate system. GK was developed at the beginning
of the twentieth century and optimized to map Germany and surrounding
countries. The global standard today, however, is the Universal Transverse
Mercator system (UTM) which is similar to GK, except that the central
meridians of the GaussKruger zones are only 3 apart, as opposed to 6 in
UTM. As a consequence, the scale variation within a GaussKruger zone is
about 1/4 of what it is in a UTM zone.
For project-oriented development, it makes sense to look at the bounding
rectangle of the example provided in JavaGPS. The map image HD.jpg
shows the famous castle in Heidelberg and can be described with two sets
of coordinates:
The constructor org.iu.gps.MapPanel() uses cartographic GK coordi-
nates:

bitmapRect.x = 3477970; bitmapRect.width = 2029;
bitmapRect.y = 5475590; bitmapRect.height = 1939;

These GK coordinates can be translated to geographic positions with

COORD.convertToLL( 3477970, 5475590 );
-> 49.41791753327985, 8.69634211847276 - upper left
COORD.convertToLL( 3477970 - 2029, 5475590 - 1939 );
-> 49.40040474786639, 8.668492617517886 - lower right

Now GeoPoint.distance can be use to determine metric coordinates. The
horizontal scale is from 0 to 2,022 meters and the vertical ranges from 0 to
1,947 meters. So the area of the map image roughly covers 2 2 kilometers.

5.3 Requirements for a Map GUI

A graphical user interface (GUI) can be used to visualize information for
a better and more intuitive understanding. The ROAF, however, will be
designed to operate without a graphical representation. Nevertheless, the
data structure should enable a mapping front end to be attached and dis-
play the graphical representation of the application. To document that the
GUI is not an essential part of the roaf , the GUI package name will be
labeled with an x , i.e., roafx , similar to the usage in the Swing Framework
in javax packages.
The three coordinate sets, GK, (lat,lon) , and (x;y), can be abstracted
to a simplified mapping device. Each coordinate set are decimal numbers
describing a horizontal and a vertical scale of a Cartesian plane. The

directions west and south are indicated by negative values.