.models {
  [zoom=17] {
    point-file: url("models/[image_z17].png");
    point-transform: translate([dx_z17],[dy_z17]);
  }
  [zoom=18] {
    point-file: url("models/[image_z18].png");
    point-transform: translate([dx_z18],[dy_z18]);
  }
  [zoom=19] {
    point-file: url("models/[image_z19].png");
    point-transform: translate([dx_z19],[dy_z19]);
  }
}