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I have a rendering problem with the mapnik GEOS plugin. I try to input a polygon WKT definition containing floats with around 16 digits. Mapnik however does not render these. When I decrease the number of digits to 5 it does work. Does anybody have a solution?

mmap.background = mapnik.Color('steelblue')
s = mapnik.Style() 
r = mapnik.Rule() 
polygon_symbolizer = mapnik.PolygonSymbolizer(mapnik.Color('#f2eff9'))
[ more style here ]
mmap.append_style('My Style',s) 

wkt_geom = 'POLYGON ((5.12345 51.6, 6.8 52.6, 7.8 51.6, 5.12345 51.6))' #DOES WORK
wkt_geom = 'POLYGON ((5.123456 51.6, 6.8 52.6, 7.8 51.6, 5.123456 51.6))' #DOES NOT WORK

layer = mapnik.Layer('wkt_layer_bla','+proj=sterea +lat_0=52.15616055555555 +lon_0=5.38763888888889 +k=0.9999079 +x_0=155000 +y_0=463000 +ellps=bessel +towgs84=565.417,50.3319,465.552,-0.398957,0.343988,-1.8774,4.0725 +units=m +no_defs')
layer.datasource =  mapnik.Geos(wkt=wkt_geom)
layer.styles.append('My Style')
mapnik.render_to_file(mmap,'/foo/bar/bla.png', 'png')
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1 Answer

up vote 1 down vote accepted

This sounds similar to the bug reported at https://github.com/mapnik/mapnik/issues/1118.

It looks like a geos specific problem, because if I move to Mapnik 2.1 and use the CSV plugin (which accepts reading WKT strings using Mapnik's internal parser not GEOS) then things seem to work just fine. I get:

Using this code:

import mapnik

m = mapnik.Map(600,300,'+init=epsg:3857')
m.background = mapnik.Color('steelblue')
s = mapnik.Style()
r = mapnik.Rule()
polygon_symbolizer = mapnik.PolygonSymbolizer(mapnik.Color('#FF3366'))
line_symbolizer = mapnik.LineSymbolizer(mapnik.Color('rgb(50%,50%,50%)'),1.0)
m.append_style('My Style',s)
# DOES NOT WORK with GEOS according to http://gis.stackexchange.com/questions/32441/mapnik-wkt-rendering-problem
# DOES seem to work fine with Mapnik's CSV plugin
wkt_geom = 'POLYGON ((5.123456 51.6, 6.8 52.6, 7.8 51.6, 5.123456 51.6))' 
csv_string = '''
''' % wkt_geom
ds = mapnik.Datasource(**{"type":"csv","inline":csv_string})
layer = mapnik.Layer('world', '+init=epsg:3857')
layer.datasource = ds
layer.styles.append('My Style')
mapnik.render_to_file(m,'world.png', 'png')
print "rendered image to 'world.png'"
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Yes, using the csv route does work. Now I know why python and geos input plugins are still experimental. –  RickyA Sep 6 '12 at 12:55
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