d3.geoTransform()

d3.geoTransform(methods)

Defines an arbitrary transform using the methods defined on the specified methods object. Any undefined methods will use pass-through methods that propagate inputs to the output stream. For example, to reflect the y-dimension (see also identity.reflectY):

var reflectY = d3.geoTransform({
  point: function(x, y) {
    this.stream.point(x, -y);
  }
});

Or to define an affine matrix transformation:

function matrix(a, b, c, d, tx, ty) {
  return d3.geoTransform({
    point: function(x, y) {
      this.stream.point(a * x + b * y + tx, c * x + d * y + ty);
    }
  });
}