Hi, A meter based scalebar cannot work very well with epsg:4326 because the more north you go the narrower is the 1 degree slice in east-west direction. Therefore you will have a different scale in the top of the map and in the bottom. Some estimate could be done according to the latitude in the middle of the image, in your case ~120 m. However, the scale is also different in the east-west and south-north directions. Use a coordinate system like UTM and the scalebar will be right. EPSG:3857 has the same trouble with scale changing according to latitude, though in a bit different way. Lappland is not as wide as in this map, not to mention the gigantic Svalbard http://osm.org/go/1mH7
-Jukka Rahkonen- Lars Lingner wrote: > Hello, > > I have an issue with the mapserver scalebar. Hopefully it is just my > understanding thats wrong. > > My data is epsg:4326 which is also used for displaying the > map requested > via wms. > > When I embed a scalebar, the length of it isn't correct. It show an > value about as twice (200+ meter) the right value (~120 m). > The region I'm displaying is in northern europe about 55.8 latitude. > > My mapfile looks like this: > > MAP > ... > UNITS METERS > EXTENT .... > ... > PROJECTION > "init=epsg:4326" > END > SCALEBAR > IMAGECOLOR 255 255 255 > LABEL > COLOR 0 0 0 > SIZE SMALL > END > STYLE 1 > SIZE 100 3 > COLOR 0 0 0 > UNITS METERS > INTERVALS 2 > POSITION lc > TRANSPARENT TRUE > STATUS EMBED > END > WEB > ... > METADATA > "wms_title" "WMS" > "wms_srs" "epsg:4326" > "wms_extent" ... > "wms_onlineresource" "http://example.com/cgi-bin/mapservice"; > ... > END > END > [LAYERCONFIGURATION] > END > > I'm using MapServer 5.6, data comes from shapefiles and Postgis-DB. > > > It is quite important to have an scalebar rendered in the image so the > user can estimate the objects length. > > I also tested the scalebar from OpenLayers and for epsg:4326 its also > wrong. When I use epsg:3857 with the geodesic=true option the scalebar > in OpenLayers looks correct. Whereas MapServer is still wrong. > > > Is MapServer able to calculate an correct scalebar for 4326? > Should I use an other projection? > In which cases does MapServer create a reliable scalebar? > > > Thank you in advance for any hints. > > > Lars > _______________________________________________ > mapserver-users mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/mapserver-users > _______________________________________________ mapserver-users mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/mapserver-users
