Polyconic projection of the Earth centered on meridian 180 degrees west, showing a bowed gap where east meets west.
I did a single polyconic projection of a Blue Marble image of the globe in an earlier article, comparing it to the sample projection in the proj (v.3) documentation. Although seemingly elongated, I called it a success. But when animated by reprojecting 360 times, varying the central meridian from -180° to +180°, I saw that something weird happens where the outside edges meet — there is sometimes, not always, a gap. I don’ t know if this is just an artifact of the projection that is to be expected, or if there’s a problem somewhere in my method or the software. You can see it in the picture at the right and in the animation below.
