Mapping Toolbox

Cutting Polygons at the Dateline

Polygon Boolean operations treat the inputs as cartesian coordinates. The polyxpoly command can be confused by geographic data that has jumps in the longitude coordinate at dateline crossings. You can prepare such geographic data for use with polybool by cutting the polygons at the dateline with the flatearthpoly command. The result of flatearthpoly is a polygon with points inserted to follow the dateline up to the pole, traverse the longitudes at the pole, and return down to the dateline crossing along the other edge of the dateline:

• [lat,lon] = scircle1(70,45,30);
  [latf,lonf] = flatearthpoly(lat,lon);
  

For the purpose of picking a pole for the dateline cut, the interior of the polygon is assumed to be in the hemisphere that contains most of the edge points. Thus a polygon produced by flatearthpoly will not cover more than a hemisphere.

Note    You do not need to use the flatearthpoly command to prepare data for a map display. The Mapping Toolbox display commands automatically cut and trim geographic data if required by the map projection.

Polygon Boolean Operations

Buffer Zones