[mkgmap-dev] Polygons deformed [Antwort]

Mon Dec 24 08:26:13 GMT 2012

The problem is the Garmin-Data-Format.

Garmin use only 24 Bit for longitude/latitude. This is for the highest 
zoom. If you reduce the zoom, then use garmin internaly only 23, 22, ... 
Bit.
The biggest number with 24 Bit is 16.777.215. Use this for 360°. From this 
it follows that 360°/16.777.215 is the minimal distance. What means that 
for example for the equator? 360° stands for around 40.075 km 
circumference of the earth. The minimal distance is for a latitude of 0° 
around 2,4m! For higher latitude it is of course higher.

I think, there is no way. 24 Bit for longitude/latitude is to less. But 
more Bits are more memory consumption and bigger maps.

See also on my web-page "Linien- und Polygonvereinfachung" 
http://technik.stinnerweb.de/Gps/garmin1.html. It is in german, but the 
pictures are language-independed ;)

Frank
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