Hi Claire, Wrapping the dateline can be a tricky issue. For maps that I've made that span the pacific, it's always been most straightforward to reproject the data into a custom projection with a central meridian in the middle of the Pacific.
If you have GDAL/OGR you could take your world_borders.shp and do this: ogr2ogr -t_srs http://spatialreference.org/ref/user/north-pacific-albers-conic-equal-area/ world_borders_pacific_albers.shp world_borders.shp ... which would reproject the shapefile into an albers equal area projection with a central meridian around -170 longitude. *Note: OGR is able to fetch the proj.4 parameters from spatialreference.org to transform the data but also excepts the proj.4 string or EPSG codes. For this projection you can fetch the proj4 string from here: from: http://spatialreference.org/ref/user/north-pacific-albers-conic-equal-area/proj4/ Then, you'll need to either specify your mapnik bbox in that map's projection of course or use mapnik to reproject your bbox like: springmeyer:~ spring$ python Python 2.5.1 (r251:54863, Jan 17 2008, 19:35:17) [GCC 4.0.1 (Apple Inc. build 5465)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> import mapnik registered datasource : gdal registered datasource : postgis registered datasource : raster registered datasource : shape >>> albers_proj = mapnik.Projection("+proj=aea +lat_1=30 +lat_2=70 +lat_0=52 +lon_0=-170 +x_0=0 +y_0=0 +ellps=GRS80 +datum=NAD83 +units=m +no_defs") >>> wgs84_bbox = mapnik.Envelope(146.27, 40.52, -173.21, 64.39) >>> mapnik.forward_(wgs84_bbox, albers_proj) Envelope(-1921935.38548,-1339056.57733,-261568.418706,2003177.44933) >>> If this were wrapped in a script it might look like: #!/usr/bin/env python from mapnik import * m = Map(600, 300) albers_proj = Projection("+proj=aea +lat_1=30 +lat_2=70 +lat_0=52 +lon_0=-170 +x_0=0 +y_0=0 +ellps=GRS80 +datum=NAD83 +units=m +no_defs") m.projection = albers_proj m.background = Color('steelblue') s = Style() r=Rule() r.symbols.append(PolygonSymbolizer(Color('#f2eff9'))) r.symbols.append(LineSymbolizer(Color('rgb(50%,50%,50%)'),0.1)) s.rules.append(r) m.append_style('My Style',s) lyr = Layer('world') lyr.datasource = Shapefile(file='data/world_borders_pacific_albers') lyr.styles.append('My Style') m.layers.append(lyr) wgs84_bbox = Envelope(146.27, 40.52, -173.21, 64.39) bbox = forward_(wgs84_bbox, albers_proj) m.zoom_to_box(bbox) render_to_file(m, 'map/world_pacific_albers.png') Cheers, Dane On May 13, 2008, at 9:21 AM, Claire McLister wrote: > Hi Everyone, > > How do I specify a map bounding box that crosses the international > date line? > > For example, if I have a bbox of (146.27, 40.52, -173.21, 64.39) I > really want a map of the Pacific Ocean region and not the whole world. > > Will appreciate any pointers. > > Claire > > -- > Claire McLister [EMAIL PROTECTED] > 21060 Homestead Road Suite 150 > Cupertino, CA 95014 408-733-2737(fax) > > http://www.zeemaps.com > > > > _______________________________________________ > Mapnik-users mailing list > [email protected] > https://lists.berlios.de/mailman/listinfo/mapnik-users _______________________________________________ Mapnik-users mailing list [email protected] https://lists.berlios.de/mailman/listinfo/mapnik-users
