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Sestier de DorsoduroThe dot on the lane

A dot that stays on the right lane

In Venice your phone’s GPS struggles: tall walls make the signal bounce and the dot jumps from one lane to another. Calletta doesn’t trust a single signal. It combines it with the map of the lanes, your steps and the compass, and learns the length of your stride on its own. The result is a steadier position, even in the narrowest lanes.

Why GPS gets it wrong in Venice

Tall buildings on both sides, covered passages, canals: the signal arrives after bouncing, and the phone thinks it is somewhere else. In Venice the lanes are narrow and close together, and one slip is enough to put you on a parallel lane.

What Calletta does

  1. It knows the lanes. It uses the real network of Venice’s walking paths (from OpenStreetMap): the dot can only be where people walk.
  2. It tries many positions at once. The filter keeps many guesses of where you are in play (a “particle filter”) and lets survive those that agree with the signal, your steps and the compass. If the signal disappears for a few seconds, the guesses keep walking with you.
  3. It counts your steps. It uses the phone’s accelerometer to tell when you are walking and how far.
  4. It learns your stride. Everyone walks differently: Calletta learns yours while you walk, when the signal is good, and remembers it.
  5. It uses the compass, but not blindly. If the compass agrees with the direction you are walking it uses it, even to choose the lane at junctions; if the phone is in a bag and the compass says random things, it switches it off.
  6. It understands where you are. It recognises when you are on a boat (and follows the signal), in a square (where you walk freely) or outside the network of lanes.
  7. It never freezes. Even with a weak signal the dot keeps moving with you.
  8. Map straight on the lane. When it is sure which lane you are on, it orients the map along the lane, because the phone’s compass is wrong near walls.

What it means for you

Your position stays yours

Your position is used on the phone to guide you and doesn’t go to our server without your consent. To tune the filter we ask for explicit consent: you can say no, and delete the recordings already sent.