Hm, no responses. Perhaps I need an easier question? :) How about a simpler case -- how can I render a simple latlon projection centered around an arbitrary dateline?
Using the world borders shapefile, I tried the following projection on the mapnik Map object: +proj=latlon +datum=WGS84 +pm=180 [full code: http://pastebin.com/f4e2b8fa1 ] This draws the eastern hemisphere on the left side of the image, with the right side blank. If I extend the bounds, I can see that the rest of the world is just clipped off to the left hand side. No good. So I used ogr2ogr to reproject the file to the new meridian: ogr2ogr -t_srs '+proj=latlong +datum=WGS84 +pm=180' world_shift.shp world.shp And tried rendering again. However, this doesn't work either. Any pointers? Am I missing something obvious here? How can I get the world to wrap around a different meridian? Thanks! On Sun, Jan 11, 2009 at 10:14 PM, Filipe Fortes <[email protected]> wrote: > I'm trying to use mapnik to render a Robinson projection centered in the > pacific ocean (example [1]). However, I've run into some issues trying to > get a correct rendering. > > I started off with the tm_world_borders shapefile [2], and re-projected it > into the robinson projection with ogr2ogr: > > ogr2ogr -t_srs '+proj=robin +lon_0=0 +x_0=0 +y_0=0 +ellps=WGS84 > +datum=WGS84 +units=m +no_defs +over' robin_world_borders.shp > tm_world_bounders.shp > > Using the following script: http://pastebin.com/f7f3b0784 -- I get a > partially correct rendering [3], due to the known issue of antarctica > (although I'm not sure why it doesn't work), so I removed antarctica using > the following ogr2ogr command: > > ogr2ogr -sql "select * from robin_world_borders where Name <> 'Antarctica'" > robin_sans_antarctica.shp robin_world_borders.shp > > Using this file, I can now get a correct rendering with a greenwich center > (sans Antarctica, of course), however I cannot get a correct rendering > centered on the dateline. I tried the following: > > 1. Specify lon_0=180 on the map's projection, as shown here: > http://pastebin.com/fc2f26a5 > > This only shows the eastern hemisphere: http://i42.tinypic.com/16h1e6h.png > (shows western only if I use lon_0=-180) > > 2. Reproject the shapefile using ogr2ogr: > > ogr2ogr -t_srs '+proj=robin +lon_0=180 +x_0=0 +y_0=0 +ellps=WGS84 > +datum=WGS84 +units=m +no_defs +over' robin_sans_antarctica.shp > robin_sans_antarctica_shifted.shp > > This produces a stranger result, where countries that span the prime > meridian are all drawn incorrectly: http://i41.tinypic.com/12542o4.png > > (code used: http://pastebin.com/f59e42e0c ) > > > Any tips on where I've gone wrong here? > > Also, if anyone knows hows to render Antarctica in the Robinson projection > that'd be great as well :) > > Thanks! > > filipe > > > [1] http://commons.wikimedia.org/wiki/File:BlankMap-World-162E.svg > [2] http://thematicmapping.org/downloads/world_borders.php > [3] http://i40.tinypic.com/2e4m8f5.png >
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