An optional helper, and a red herring in the most literal sense. Nothing on this page knows about any puzzle. It runs entirely in your browser and keeps working once it has loaded, even with no signal.
The herring
This herring is not a clue.
Tap the herring (or Flap) to make it flap. When you project a waypoint or measure between two points below, it turns to face that way, with north at the top.
Point the herring: project a waypoint
Start somewhere, face a bearing, walk a distance: where do you end up?
How far and which way
The distance between two points, and the bearing to walk from the first to reach the second.
Through the herring's eye
Look at a picture through a fish-eye lens, and turn or flip it. Your picture stays on this device; nothing is uploaded. Tap the picture to move the lens, use the two lens sliders, or click the picture and use the arrow keys.
“Put the herring’s heading at the top” turns the picture so the direction the herring is pointing faces up, the way you’d hold a photo of a map while walking that way. “Straighten it out” undoes turning and flipping; the lens stays as you set it.
How it works
Both calculations use Thaddeus Vincenty's 1975 formulas on the WGS84 ellipsoid, the shape of the Earth that GPS receivers use. They were checked against Vincenty's own worked example (Flinders Peak to Buninyong, 54,972.271 metres), and agree with it to under a millimetre. For two points on almost exactly opposite sides of the Earth, where those formulas can fail to settle, the page falls back to a sphere and says so.
Bearings are true bearings, measured clockwise from true north. A magnetic compass points to magnetic north, which differs by the local declination, so if a puzzle's bearing is magnetic, correct it first.
The fish-eye lens only moves pixels around: inside the lens, each point takes the colour of a point nearer the lens's centre (or further out, for a negative strength, which pinches). Turning and flipping work the same way, without blending neighbouring pixels, so every pixel you see is one of the picture's own, moved. No colour is changed, and none is shown as a number.
Coordinates can be typed the geocaching way (N 45° 12.345 W 093° 54.321), as decimal degrees (45.20575, -93.90535), or as degrees, minutes and seconds. Without an N, S, E or W, positive numbers are read as north and east, so the page always shows how it read what you typed.