Hi, it's up to you, what resolutions or scales you want take. How it best match in your map div. The commercial layers use a resolution array with maxResolution=156543.0339/zoomLevel with zoomLevel = 0 - n. As far as I know for maxResolution the world match in a square of 256x256 pixel. For EPSG:4326 OL suggest a maxResolution=1.40625 = 360/256. The world match in a rectangle of 256x128 pixel. It's a practical choice, the world boundary is always a tile boundary. I use map.layers[0].resolutions => [500, 250, 125, 62.5, 31.25, 15.625, 7.8125, 3.90625, 1.953125, 0.9765625, 0.48828125, 0.244140625, 0.1220703125, 0.06103515625, 0.030517578125, 0.0152587890625]; that is in scales map.layers[0].scales => [1417323.5999999999, 708661.7999999999, 354330.89999999997, 177165.44999999998, 88582.72499999999, 44291.362499999996, 22145.681249999998, 11072.840624999999, 5536.420312499999, 2768.2101562499997, 1384.1050781249999, 692.0525390624999, 346.02626953124997, 173.01313476562498, 86.50656738281249, 43.253283691406246];
to display Nordrhein-Westfalen in my map with a size of 900x600 pixel. It's a practical choice. For the maxResolution=500 NRW matches in the map div. If you declare a maxExtent in the map options and set resolution to auto, OL calculates a resolution from the maxExtent and the map div. So I would think, it's always a practical choice, what resolution you take. Viele Grüße, Arnd _____ Von: [email protected] [mailto:[email protected]] Im Auftrag von Robert Buckley Gesendet: Dienstag, 6. Dezember 2011 19:15 An: [email protected] Betreff: Re: AW: [OpenLayers-Users] Creating an application with pre-definedmapscales/resolutions Hi, Thanks. "The differences between the different projections is, that the meter doesn't describe the real length." ...ok I think I see...you mean that google distorted the projection so it fits nicely in a square whereas the others are "real" projected coordinate systems? But what I was really asking is that why have I seen so many different resolutions for various maps. cheers, Rob . _____ Von: Arnd Wippermann <[email protected]> An: 'Robert Buckley' <[email protected]> Cc: [email protected] Gesendet: 19:01 Dienstag, 6.Dezember 2011 Betreff: AW: [OpenLayers-Users] Creating an application with pre-defined mapscales/resolutions 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: [email protected] [mailto:[email protected]] Im Auftrag von Robert Buckley Gesendet: Dienstag, 6. Dezember 2011 08:48 An: [email protected] 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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