feat: Add post: Max speed Overpass

content/posts/2025/01/max-speed-overpass.md

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+---
+title: 'Getting the max speed of a way using Overpass API'
+description: 'A random small project done the day before an exam'
+author: Appuchia
+date: 2025-01-20
+categories:
+    - Linux
+    - Cars
+    - API
+    - Development
+    - OSM
+tags:
+    - Overpass
+    - Learning
+    - Utility
+    - Afternoon project
+# cover:
+#     image: '/images/Max Speed Overpass'
+---
+
+# The idea
+
+This video from a really nice channel I follow popped up on my YouTube feed,
+and I thought it was a really nice idea, and I thought showing the max speed as well as the current speed would be really useful.
+
+{{< youtube RdmgdWnIlKY >}}
+
+The first thing I needed was to get the current location, but I know it's relatively easy to do once you have a GPS module.
+
+So the next thing I needed was to get the max speed of the road I'm on.
+I thought of using OpenStreetMap for this, I searched in the wiki for some API to use, and I found the official OSM API.
+It also listed the Overpass API for read-only access to the OSM data, which was what I would use anyways, so I decided to use that.
+
+However, here's how to get info on an OSM way once you have the way ID (this example uses London's M25):
+
+```http
+GET https://www.openstreetmap.org/api/0.6/way/27731013
+```
+
+# The Overpass API
+
+You can access a really nice web interface here: [Overpass Turbo](https://overpass-turbo.eu/)
+
+However, what you want is the data itself, so you can use the API that returns the data.
+
+I'll use JSON as it's easier to parse.
+
+Here's how to get the details of a road knowing its ID using the Overpass API:
+
+```http
+GET https://overpass-api.de/api/interpreter?data=[out:json];way['highway'](27731013);out;
+```
+
+It also works using POST requests (which I prefer even though they require a bit more work):
+
+```http
+POST https://overpass-api.de/api/interpreter
+
+data=[out:json];way['highway'](27731013);out;
+```
+
+However, what I wanted was to get the closest way to some coords (given by the GPS module),
+so I needed to use the `way` query with the `around` filter.
+
+Here's how to get the closest road to some coords using the Overpass API:
+
+```http
+POST https://overpass-api.de/api/interpreter
+
+data=[out:json];way['highway'](around:radius,lat,lon);out;
+```
+
+`radius` is the radius in meters, and `lat` and `lon` are the coordinates.
+
+# What I ended up with
+
+That's really nice, but it returns a lot of data, and I only need the max speed.
+
+I decided to use `jq` to parse the JSON and get the max speed, stored as `maxspeed` in the way tags.
+
+Here's the command I used:
+
+```bash
+curl -fsSL -X POST https://overpass-api.de/api/interpreter -d "data=[out:json];way['highway']['maxspeed'](around:10,lat,lon);out;" | jq -r '.elements[0].tags.maxspeed'
+```
+
+The query includes `['highway']['maxspeed']` to filter the roads that have a `maxspeed` tag.
+
+I added the `-fsSL` flags to `curl` to make it silent and follow redirects, and the `-r` flag to `jq` to make it return the raw string.
+
+# Conclusion
+
+I think this is a really nice project, and I'll probably do it after my exams.
+
+Also, I created a ZSH function to store this research mid-term until I actually do it:
+
+```zsh
+getmaxspeed() {
+    export lat=$argv[1]
+    export lon=$argv[2]
+    export radius=$argv[3]
+
+    if [ -z $lat ] || [ -z $lon ]; then
+        echo "Usage: getmaxspeed <lat> <lon> [radius]"
+        return 1
+    fi
+
+    # Default radius
+    if [ -z $radius ]; then
+        radius=10
+    fi
+
+
+    curl -fsSL -X POST 'https://overpass-api.de/api/interpreter' \
+        # -H "Content-Type: application/x-www-form-urlencoded" \
+        -d "data=[out:json][timeout:5];way['highway']['maxspeed'](around:$radius,$lat,$lon);out;" \
+    | jq -r ".elements[0].tags.maxspeed"
+}
+```
+
+---
+
+Thanks for reading!
+
+Done with 🖤 by Appu.