[OSM-talk] Wrong scale bar :(

[Juan Lucas Dominguez Rubio]

Since I said it is wrong, I think I should provide the way to solve it :
 
- We can use the latitude of the center of the view to compute the scale, though this will be inaccurate when we are in zooms 0 to 5 approx. Let L be the latitude of the center of the view.
 
- In zoom z each parallel is covered by 2^z tiles.
 
- The length in meters of the paralel is 40,000,000 * cos(L)
 
- So the width/height of each tile can be assumed to be:
 
40,000,000 * cos(L) / 2^z
 
In the case of Linkoping:
 
L = 58.4
z = 18
 
tile w/h = 80 m.
 
Cheers,
Lucas

________________________________

De: Juan Lucas Dominguez Rubio
Enviado el: jue 17/04/2008 1:37
Para: talk at openstreetmap.org
Asunto: Wrong scale bar :(


Reusing Lars Aronsson's message, we can see that the new scale bar is wrong. The buildings in this screenshot should be 32 x 11 m (attached example.jpg)
 
Cheers,
Lucas
 
-------------
[...]
I've never cared too much about that scale, but now I know that 
these apartment buildings along Syrengatan are 11 x 32 metres and 
not 22 x 64 metres as JOSM would lead you to believe, 
http://www.openstreetmap.org/?lat=58.407&lon=15.600&zoom=17&layers=0BFT
[...]
-- 

  Lars Aronsson (lars at aronsson.se)
  Aronsson Datateknik - http://aronsson.se <http://aronsson.se/> 
 
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