[OpenLayers-Users] Formula for calculating resolution?

[Arnd Wippermann]

Hello Linda,
 
to get myself some knowledge with scales and resolutions, i have build a
little example. The resolution for your extent must be 0.00009633333333333
(= dx/WIDTH), then you get - with the right centerpoint - your area.
Change in your resolutions 0.0000858306884765625 with 0.00009633333333333.
One hint: to set own resolutions for google layers is not possible.

To calculate scales for various units you must keep in mind to take the
right factor. Also must dx/WIDTH=dy/HEIGHT.

Einheit Faktor
inches        1
ft           12
mi        63360
m            39,3701
km        39370,1
dd      4374754
in            1
 
dpi       72                   
Einheit   dd                   
Faktor    4374754
 
Left         -122,1655000                   
Right        -122,1077000                   
Top            43,0083000                   
Bottom         42,9505000                   
WIDTH         600          pixel
HEIGHT        600          pixel
dx              0,0578     LE
dy              0,0578     LE
Scale       30343,29374                   
Resolution      0,000096333333                   
 
Scale = dx/WIDTH * dpi * Faktor
Resolution = dx/WIDTH

I hope that will help to solve your problem.

Mit freundlichen Grüssen

Arnd Wippermann
http://gis.ibbeck.de/ginfo/


________________________________

Von: users-bounces at openlayers.org [mailto:users-bounces at openlayers.org] Im
Auftrag von Linda Rawson
Gesendet: Mittwoch, 26. September 2007 06:05
An: users at openlayers.org
Betreff: [OpenLayers-Users] Formula for calculating resolution?


I have a legacy mapping system that I am trying to convert to openlayers.
MG.  It is bad.
 
Anyway, I have the following dimensions of a 600 X 600 window.
var bounds = new OpenLayers.Bounds(-122.1655, 42.9507, -122.1077, 43.008);

I need the four lat/lon corners to be exactly these numbers at a certain
zoom level.  What would I set as the resolution in the resolution array to
get this?

My resolution array is the following:

var layerResolutions =
[0.703125,0.17578125,0.0439453125,0.0054931640625,0.0006866455078125,0.00017
1661376953125,0.0000858306884765625,0.00004291534423828125,0.000021457672119
140625,0.000010728836059570312];

Thanks in advance,

Linda Rawson

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.osgeo.org/pipermail/openlayers-users/attachments/20070927/fc513ad5/scalesandresolutions.html