AW: [OpenLayers-Users] Creating an application with pre-defined mapscales/resolutions

[Arnd Wippermann]

Hi,
 
it should be correct. 1 meter is always 1 meter. The differences between the
different projections is, that the meter doesn't describe the real length.
 
EPSG:25832 is a projection, where a meter on map is a meter in reality.
For i.e. EPSG:900913 (Google Projection) it's not.
 
Distance Düsseldorf - Hannover 
 
EPSG:25832 : 240.9911275436498
EPSG:900913 : 389.3661105393922

 
Arnd

  _____  

Von: openlayers-users-bounces at lists.osgeo.org
[mailto:openlayers-users-bounces at lists.osgeo.org] Im Auftrag von Robert
Buckley
Gesendet: Dienstag, 6. Dezember 2011 08:48
An: users at openlayers.org
Betreff: [OpenLayers-Users] Creating an application with pre-defined
mapscales/resolutions


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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