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When using Cartodb to layer polygons (craters on Mercury) on top of a user-defined (via Mapbox) basemap, features (craters/polygons) that span the edge of the basemap are extended into bands that wrap the planet/map and exclude the crater they should encircle.

Example of crater-polygons to bands

Is there an elegant way to fix this? Here's a link to the visualisation: Edge Spanning Polygon Anomalies

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2 Answers 2

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Try to split the features that cross the dateline (-180/180 longitude) . ogr2ogr utility has an option -wrapdateline to do this.

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  • Thanks @spatialthoughts. I've heard of this solution but didn't know ogr2ogr had that functionality. I fear however that splitting the polygons like that will make further processing of them in my workflow difficult; I need each polygon to be a single entity (I could add pre- and post- processing steps to my workflow around the visualisation step but I'm hope for a more 'elegant' solution).
    – DrJMcAuliffe
    Mar 17, 2015 at 14:37
  • CartoDB deals with multipolygons though, so you can split them and still have them be considered a single entity
    – andrewxhill
    Mar 18, 2015 at 11:55
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There's an inelegant way to do it. If your table SQL originally looked like this and your the_geom column was original in geographic coordinates:

SELECT * FROM mytable;

You'd replace it with:

SELECT 
 cartodb_id, myattribute1, myattribute2, the_geom,
 ST_Transform(
 ST_Difference(
 ST_Difference(the_geom,
 ST_Buffer('SRID=4326;LINESTRING(180 -89, 180 89)'::geometry, 0.00001)), 
 ST_Buffer('SRID=4326;LINESTRING(-180 -89, -180 89)'::geometry, 0.00001)), 
 3857) AS the_geom_webmercator
FROM mytable

To make it more efficient, wrap the differencing step in a CASE statement and only difference geometries that meet an ST_Intersects() condition with the -180 or 180 boundary lines.

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