A couple of functions to help with geographic coordinates. To start you just need to set the geo::pixelSize viariable, it's the size of your equiretangular map
//!Translates a Latitude and Longitude to a Cartesian point in a equiretangular map
ci::vec2 coordinateToCartesian(const Coordinate coordinate , ci::vec2 mapSize = pixelSize);
//!Translates a cartesian point to Latitude and Longitude
Coordinate cartesianToCoordinate(const ci::vec2& point, ci::vec2 size = pixelSize);
//! Returns the distance between two coordinates
double distanceCoordinate(const Coordinate& coordA, const Coordinate coordB);
//! Returns a coordinate point in the terminator line
Coordinate getTerminatorCoords(float lat, float lon, float gamma)