[OpenLayers-Users] Creating an application with pre-defined map scales/resolutions

[Robert Buckley]

Hi,

I would like to have a simple application which delivers wms layers in scales/resolutions which are not the usual OSM/Google messy scales, but rather include 1:1000 000 / 1:500 000 / 1:250 000 / 1:100 000 / 1: 50 0000/ 1:10 000, 1: 5000 and 1:2,500. To make this even more difficult I need to do this in EPSG:25832 the european standard ETRS/ UTM zone 32 projected CRS with units of meters

As far as I have understood, this is fully dependant on the basemap resolutions. As this is pure mathematical I would like to show what I think I have learnt and wait for comments....


R = resolution 
S = scale as denominator
IPU = OpenLayers.INCHES_PER_UNIT[units] = 39.3701 inches in a meter
DPI = OpenLayers.DOTS_PER_INCH = 25.4 / 0.28 = 90.71428571428571 ( 1 inch = 25.4 mm / standardized pixel size of 0.28x0.28mm)
this must be set in the application code "OpenLayers.DOTS_PER_INCH = 25.4 / 0.28" = 90.7142   otherwise, the scale factor would be 72 / 90.7143 = 0.7937.

R= S / IPU * DPI

using this formular, we are basically working out how many pixels there are in 1 meter of screen, to so find out how many pixels there are in 1000000 meters of screen we use...

[Scale 1:1000 000]

R = 1000000  / (39.2701 * 90.71428571428571) 
R =1000000  / 3562.359071428571260271
R = 280.712859077111976006937033


[Scale 1:500000]

R = 500000  / (39.2701 * 90.71428571428571) 
R =500000  / 3562.359071428571260271
R = 140.356429538555988003468517

...etc for the 1:250 000 / 1:100 000 ...



What bothers me though, is that every EPSG code with units of meters will have the same resolutions. Is this correct?


sources: 
http://geowebcache.org/docs/current/concepts/gridsets.html
http://wiki.osgeo.org/wiki/WMS_Tiling_Client_Recommendation
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