Bench to Bench: Using Gemma to Find Benches in Kolkata

Description and use

Bench to Bench uses Gemma to find benches in Kolkata where OpenStreetMap lacks data, enabling safe walks with a seat within 150 m.

Problem

Finding a place to sit within 150 m during a walk for someone with knee pain, when map data lacks benches.

Outcome

Gemma identified 7 benches in Kolkata from 165 photos, enabling a 254 m walk loop with a seat within 69 m, whereas the map alone could not plan any safe walk.

Workflow

• 1. Extract streets from OpenStreetMap via Overpass API and build a walking graph, removing steps, gravel, cobblestones, private paths and slopes over 6%.
• 2. Pull 165 street photos of Kalighat‑Hazra from Mapillary.
• 3. Run Gemma 4 E4B locally with Ollama on an RTX 5060 laptop to analyze each photo, outputting a fixed‑format JSON indicating presence of a seat, steps, broken footpath, shade, and a brief explanation.
• 4. Validate each Gemma output against the required format; discard failures.
• 5. Seed a search that hops from seat to seat, accepting only loops where every stretch is ≤150 m.
• 6. In the browser, download streets and benches within 900 m of the user, plan the walk, and use Chrome’s built‑in voice to give spoken cues while the phone stays in a pocket.
• 7. During the walk, the app announces the next seat and its distance, keeping the user within 150 m of a seat.
• 8. After the walk, the user can review the route and seat locations.
• 9. Iterate on model choice (E4B vs E2B) and adjust rules for steps and shade based on validation results.

Evidence

OpenStreetMap knows 0 places to sit. Map only, the app says "No safe walk possible here." Anyone who has walked in Kolkata knows that's wrong.

Source

Gemma found 7 places to sit in 165 photos (mostly low ledges and platforms in front of shops, plus chairs outside one shop).

Source

Result in Kolkata: Gemma found 7 places to sit in 165 photos... With those, the app plans a 254 m loop where you are never more than 69 m from a seat.

Source

I pulled 165 street photos of Kalighat‑Hazra from Mapillary.

Source