[ka-Map-users] ka-Map Maths

Christopher Brown chris at basebloc.com
Thu Aug 24 07:03:47 EDT 2006

Hi Guys,

I've been studying the tile generation code for ka-map and as I'm not used
GIS type calculations am having some trouble with understanding some of the
maths regarding scale etc, in the kaMap zoomToExtents method, especially the
following line and its significance: this.cellSize =
newScale/(oMap.resolution * inchesPerUnit[oMap.units]);, which translates in
my case to scale/(72*39.3701).

For example if I had the following 529.166 = 1500000/(2834.6472) with the
first part being my scale and the second part being how many pixels there
are in a meter, what is the significance of 529.166?

The cellsize variable is then used in the later equations and methods to
ultimately produce the tiles in tile.php without having to pass a geo extent
for each image to tile.php, I have been modifying the system and it works
but I would like to understand how it is working, if anyone has any insight
for someone who should have paid more attention to his maths teacher at
school, it would be most appreciated.



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