[SOLVED! [Proj] Re: Problem overlaying georeferenced images in Google,
jorge.arevalo at gmail.com
Thu Jun 12 06:07:29 EDT 2008
Ok' I've solved the problem!!
One important thing that I hadn't considered was that Google Maps
changes the meters-per-pixel ratio not only when you change the zoom
level, but also with the latitude. If you move the map upper or lower
(in vertical direction), this ratio changes.
I think that there is a good reason for this: Mercator projection
"stretchs" the shapes near to poles (North and South), and maybe google
wants to minimize the effect by changing the meter-per-pixel ratio
I was considering that this ratio remained constant for each zoom level.
Now, I calculate it with this formula:
m/px = cos(latitud) * ( 1 / 2^(zoom+8) ) * 40075017
That I got from http://slappy.cs.uiuc.edu/fall06/cs492/Group2/example.html
And now... it works!! I realize that when I was checking the coordinates...
Thanks a lot, anyway. You' ve helped me!
> Usually you do what ever to fit the shape, if you are sure that the reference shape
> is the correct one. Nobody cares about the map borders. It is more important
> to have the places where they are.
> Take some known points and make sure their coordinates are correct on
> any map and then start to deal with the rest of the problem...
> Regards: Janne.
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