From 105651f0052209f6f1cfbc2a27c08efddd4b9e11 Mon Sep 17 00:00:00 2001
From: Roman Priesol <roman@priesol.net>
Date: Mon, 7 Sep 2026 13:38:49 +0200
Subject: [PATCH] Add activity type and a click-to-open track profile panel
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Track properties gain activity_type (FIT: sport enum from the
session/sport message, Garmin's own table; GPX: <trk><type> passed
through as-is) alongside the existing distance/elevation/duration.

Clicking a track line now opens a bottom panel with a chart per
metric the track actually has (elevation always; speed/cadence/heart
rate only when present — FIT's record fields or GPX's device
extensions). TrackStats.build_profile computes cumulative distance
the same way for both formats so they're directly comparable. One
pointermove listener drives a synchronized crosshair across every
chart, a single tooltip listing all series, and a map marker at the
hovered point's position — hovering the chart shows where on the
track that moment was.
---
 docs/architecture.adoc     |  69 +++++++++---
 lib/maptool/fit.rb         |  96 +++++++++++++---
 lib/maptool/gpx.rb         |  25 ++++-
 lib/maptool/track_stats.rb |  27 +++++
 public/css/style.css       | 112 +++++++++++++++++++
 public/js/gpx.js           |  21 +++-
 public/js/map.js           |   5 +-
 public/js/track_profile.js | 218 +++++++++++++++++++++++++++++++++++++
 test/fixtures/sample.gpx   |  13 +++
 test/test_fit.rb           |  64 +++++++++++
 test/test_gpx.rb           |  13 +++
 test/test_track_stats.rb   |  22 ++++
 views/index.erb            |   9 ++
 views/layout.erb           |   3 +-
 14 files changed, 655 insertions(+), 42 deletions(-)
 create mode 100644 public/js/track_profile.js

diff --git a/docs/architecture.adoc b/docs/architecture.adoc
index 408c206..de48cbe 100644
--- a/docs/architecture.adoc
+++ b/docs/architecture.adoc
@@ -234,21 +234,60 @@ matched URL can never break out of the `href="..."` attribute. Every
 other value is HTML-escaped before being handed to `Popup#setHTML`.
 
 Track properties:: Every track feature (both formats) also carries
-`distance_meters`, `elevation_gain_meters`, `duration_secs` and
-`point_count`, computed once server-side by `Maptool::TrackStats`
-(`lib/maptool/track_stats.rb`, shared by `Gpx`/`Fit` so neither
-duplicates the haversine formula) rather than in the browser — cheap
-either way, but it means a GPX and a FIT file end up with the same
-properties shape, so the frontend doesn't need to know which format it
-got. Distance sums the haversine distance between consecutive points;
-elevation gain sums only the positive deltas (descents don't
-subtract); duration is the gap between the first and last known
-timestamp, skipping unknown ones in between — `nil` for any of these
-where the source data doesn't have enough to compute it (e.g. a GPX
-file with no `<time>` elements has `duration_secs: nil`). Hovering a
-track line (rather than clicking, unlike a waypoint — these properties
-describe the whole line, not whichever point the cursor happens to be
-over) shows them in the same popup mechanism.
+`distance_meters`, `elevation_gain_meters`, `duration_secs`,
+`point_count` and `activity_type`, computed once server-side by
+`Maptool::TrackStats` (`lib/maptool/track_stats.rb`, shared by
+`Gpx`/`Fit` so neither duplicates the haversine formula) rather than
+in the browser — cheap either way, but it means a GPX and a FIT file
+end up with the same properties shape, so the frontend doesn't need to
+know which format it got. Distance sums the haversine distance between
+consecutive points; elevation gain sums only the positive deltas
+(descents don't subtract); duration is the gap between the first and
+last known timestamp, skipping unknown ones in between — `nil` for any
+of these where the source data doesn't have enough to compute it (e.g.
+a GPX file with no `<time>` elements has `duration_secs: nil`).
+`activity_type` comes from wherever each format keeps it: FIT's
+`session`/`sport` message has a `sport` enum field (`Fit::SPORT_NAMES`
+— Garmin's own table, github.com/garmin/fit-python-sdk's `profile.py`,
+not exhaustive of every value Garmin has defined but every mainstream
+one); GPX's `<trk><type>` is free text, whatever a device/app chose to
+write, passed through as-is. Hovering a track line (rather than
+clicking, unlike a waypoint — these properties describe the whole
+line, not whichever point the cursor happens to be over) shows them in
+the same popup mechanism as waypoints; the popup also hints that
+clicking opens the full profile panel below.
+
+Track profile panel:: Clicking a track line opens a bottom panel
+(`public/js/track_profile.js`, `TrackProfilePanel`) with a chart per
+metric the track actually has data for — elevation always (assuming
+any point carries an `<ele>`/altitude), speed/cadence/heart rate only
+when present. `Maptool::TrackStats.build_profile` (called from both
+`Gpx`/`Fit`, alongside `.compute` above) produces this: one entry per
+point with cumulative distance (computed the same way for every
+format, not trusted from a device's own odometer field, so a GPX and a
+FIT track are directly comparable), elevation, and whatever
+speed/cadence/heart-rate extras that point's format/file carried —
+`nil` fields simply don't render their chart. For FIT, those extras
+are the `record` message's own `heart_rate`/`cadence`/`speed` fields
+(3/4/6); for GPX, a device-specific `<extensions>` block under each
+`<trkpt>` — usually Garmin's `TrackPointExtension`, matched by local
+element name only (`hr`/`cad`/`speed`) so it doesn't care which XML
+namespace prefix a given file happens to declare.
++
+Each chart is its own single-series `<svg>` (elevation/speed/cadence/
+heart rate are on wildly different scales, so this is small multiples
+rather than one chart with several y-axes) with a fixed `viewBox` width, stretched to
+the container by CSS; mouse interaction converts `clientX` through the
+container's current `getBoundingClientRect()` on every move rather
+than fighting the SVG's own coordinate transform, so it stays correct
+across container width without redrawing — though a browser resize
+while the panel is open won't reflow the already-drawn paths until
+it's reopened. One `pointermove` listener on the whole chart container
+(not per-chart) finds the nearest profile point by distance and drives
+three things at once: a synchronized crosshair line in every chart, a
+single tooltip listing every active series' value at that point, and a
+MapLibre `Marker` moved to that point's `lon`/`lat` on the map — so
+hovering the chart shows where on the track that moment actually was.
 
 == Live GNSS position
 
diff --git a/lib/maptool/fit.rb b/lib/maptool/fit.rb
index 5e1a945..4fc80b4 100644
--- a/lib/maptool/fit.rb
+++ b/lib/maptool/fit.rb
@@ -4,23 +4,47 @@ module Maptool
   # Converts a Garmin FIT file (binary — see https://developer.garmin.com/fit/)
   # to a GeoJSON FeatureCollection, in the same shape Gpx.to_geojson produces
   # for a <trk>: one Feature per file, geometry MultiLineString, "kind" =>
-  # "track". Only positioned "record" messages are read — FIT also carries
-  # laps/sessions/events/device info/developer fields, none of which this
-  # app has anywhere to show, so they're skipped by byte-length rather than
+  # "track". Only "record" messages (the track points) and one "sport"/
+  # "session" field (the activity type) are read — FIT also carries laps,
+  # events, device info, developer fields, none of which this app has
+  # anywhere to show, so they're skipped by byte-length rather than
   # interpreted.
   module Fit
     class ParseError < StandardError; end
 
     FIT_EPOCH = Time.utc(1989, 12, 31).to_i
     RECORD_MESSAGE_NUM = 20
+    SPORT_MESSAGE_NUM = 12
+    SESSION_MESSAGE_NUM = 18
     FIELD_POSITION_LAT = 0
     FIELD_POSITION_LONG = 1
     FIELD_ALTITUDE = 2
+    FIELD_HEART_RATE = 3
+    FIELD_CADENCE = 4
+    FIELD_SPEED = 6
     FIELD_TIMESTAMP = 253
     FIELD_ENHANCED_ALTITUDE = 78
+    SPORT_FIELD_BY_MESSAGE = { SPORT_MESSAGE_NUM => 0, SESSION_MESSAGE_NUM => 5 }.freeze
     SEMICIRCLE_TO_DEGREES = 180.0 / (2**31)
 
+    # Garmin's own sport enum (github.com/garmin/fit-python-sdk's
+    # profile.py, `types.sport`) — not exhaustive of every value Garmin has
+    # ever defined (rare ones omitted), but every mainstream activity type.
+    SPORT_NAMES = {
+      0 => "generic", 1 => "running", 2 => "cycling", 3 => "transition",
+      4 => "fitness_equipment", 5 => "swimming", 6 => "basketball", 7 => "soccer",
+      8 => "tennis", 9 => "american_football", 10 => "training", 11 => "walking",
+      12 => "cross_country_skiing", 13 => "alpine_skiing", 14 => "snowboarding",
+      15 => "rowing", 16 => "mountaineering", 17 => "hiking", 18 => "multisport",
+      19 => "paddling", 20 => "flying", 21 => "e_biking", 22 => "motorcycling",
+      23 => "boating", 24 => "driving", 25 => "golf", 30 => "inline_skating",
+      31 => "rock_climbing", 32 => "sailing", 33 => "ice_skating", 37 => "stand_up_paddleboarding",
+      38 => "surfing", 39 => "wakeboarding", 40 => "water_skiing", 41 => "kayaking",
+      49 => "baseball", 53 => "diving", 62 => "hiit", 87 => "geocaching", 88 => "canoeing"
+    }.freeze
+
     Definition = Struct.new(:global_mesg_num, :little_endian, :fields, :total_size)
+    ParseResult = Struct.new(:records, :activity_type)
 
     def self.kinds(path)
       to_geojson(path)["features"].empty? ? [] : ["track"]
@@ -29,16 +53,21 @@ module Maptool
     end
 
     def self.to_geojson(path)
-      records = parse(File.binread(path))
-      features = records.empty? ? [] : [track_feature(records.map(&:first), records.map(&:last))]
+      result = parse(File.binread(path))
+      features = result.records.empty? ? [] : [track_feature(result)]
       { "type" => "FeatureCollection", "features" => features }
     end
 
-    def self.track_feature(coordinates, times)
+    def self.track_feature(result)
+      coordinates = result.records.map { |r| r[:coordinate] }
+      extras = result.records.map { |r| { speed_mps: r[:speed_mps], cadence_rpm: r[:cadence], heart_rate_bpm: r[:heart_rate] } }
+
       {
         "type" => "Feature",
         "geometry" => { "type" => "MultiLineString", "coordinates" => [coordinates] },
-        "properties" => { "kind" => "track", "name" => nil }.merge(TrackStats.compute(coordinates, times: times)),
+        "properties" => { "kind" => "track", "name" => nil, "activity_type" => result.activity_type }
+          .merge(TrackStats.compute(coordinates, times: result.records.map { |r| r[:time] }))
+          .merge("profile" => TrackStats.build_profile(coordinates, extras: extras)),
       }
     end
     private_class_method :track_feature
@@ -54,6 +83,7 @@ module Maptool
       offset = header_size
       definitions = {}
       records = []
+      activity_type = nil
 
       while offset < data_end
         header = data.getbyte(offset)
@@ -62,7 +92,8 @@ module Maptool
         if header & 0x80 != 0
           local_type = (header >> 5) & 0x3
           definition = definitions[local_type] or raise ParseError, "data message before its definition"
-          offset = read_data_message(data, offset, definition, records)
+          offset, sport = read_data_message(data, offset, definition, records)
+          activity_type ||= sport
         elsif header & 0x40 != 0
           local_type = header & 0x0F
           definition, offset = read_definition(data, offset, header & 0x20 != 0)
@@ -70,11 +101,12 @@ module Maptool
         else
           local_type = header & 0x0F
           definition = definitions[local_type] or raise ParseError, "data message before its definition"
-          offset = read_data_message(data, offset, definition, records)
+          offset, sport = read_data_message(data, offset, definition, records)
+          activity_type ||= sport
         end
       end
 
-      records
+      ParseResult.new(records, activity_type)
     rescue ArgumentError, NoMethodError => e
       raise ParseError, e.message
     end
@@ -107,20 +139,38 @@ module Maptool
     end
     private_class_method :read_definition
 
+    # Returns [next_offset, sport_name_or_nil] — the latter only set when
+    # this message happens to be the one sport/session message carrying it.
     def self.read_data_message(data, offset, definition, records)
+      sport = nil
       if definition.global_mesg_num == RECORD_MESSAGE_NUM
         record = extract_record(data, offset, definition)
         records << record if record
+      elsif (field_num = SPORT_FIELD_BY_MESSAGE[definition.global_mesg_num])
+        sport = extract_sport(data, offset, definition, field_num)
       end
-      offset + definition.total_size
+      [offset + definition.total_size, sport]
     end
     private_class_method :read_data_message
 
-    # Only reads the 4 fields the map/its properties need; every other
-    # field in the message (heart rate, cadence, power, ...) is walked past
-    # via its declared size without being interpreted.
+    def self.extract_sport(data, offset, definition, target_field_num)
+      pos = offset
+      definition.fields.each do |field_num, size|
+        if field_num == target_field_num
+          value = unpack_int(data, pos, size, definition.little_endian, signed: false)
+          return SPORT_NAMES[value]
+        end
+        pos += size
+      end
+      nil
+    end
+    private_class_method :extract_sport
+
+    # Only reads the fields the map/its properties need; every other field
+    # in the message (power, temperature, ...) is walked past via its
+    # declared size without being interpreted.
     def self.extract_record(data, offset, definition)
-      lat = lon = altitude = timestamp = nil
+      lat = lon = altitude = timestamp = heart_rate = cadence = speed = nil
       pos = offset
 
       definition.fields.each do |field_num, size|
@@ -133,6 +183,12 @@ module Maptool
           altitude ||= unpack_int(data, pos, size, definition.little_endian, signed: false)
         when FIELD_TIMESTAMP
           timestamp = unpack_int(data, pos, size, definition.little_endian, signed: false)
+        when FIELD_HEART_RATE
+          heart_rate = unpack_int(data, pos, size, definition.little_endian, signed: false)
+        when FIELD_CADENCE
+          cadence = unpack_int(data, pos, size, definition.little_endian, signed: false)
+        when FIELD_SPEED
+          speed = unpack_int(data, pos, size, definition.little_endian, signed: false)
         end
         pos += size
       end
@@ -142,7 +198,11 @@ module Maptool
       coordinate = [lon * SEMICIRCLE_TO_DEGREES, lat * SEMICIRCLE_TO_DEGREES]
       coordinate << (altitude / 5.0 - 500) if altitude && !invalid?(altitude, 2) && !invalid?(altitude, 4)
       time = Time.at(FIT_EPOCH + timestamp).utc if timestamp && !invalid?(timestamp, 4)
-      [coordinate, time]
+      heart_rate = nil if heart_rate.nil? || invalid?(heart_rate, 1)
+      cadence = nil if cadence.nil? || invalid?(cadence, 1)
+      speed_mps = speed && !invalid?(speed, 2) ? speed / 1000.0 : nil
+
+      { coordinate: coordinate, time: time, heart_rate: heart_rate, cadence: cadence, speed_mps: speed_mps }
     end
     private_class_method :extract_record
 
@@ -164,8 +224,8 @@ module Maptool
 
     # FIT's per-base-type "field not present" sentinel: all bits set for an
     # unsigned/positive-only reading, the same pattern for signed. Good
-    # enough for the two fields this cares about (position, altitude)
-    # without needing every base type's exact invalid value.
+    # enough for the fields this cares about without needing every base
+    # type's exact invalid value.
     def self.invalid?(value, size)
       value == (1 << (size * 8 - 1)) - 1 || value == -1 || value == (1 << (size * 8)) - 1
     end
diff --git a/lib/maptool/gpx.rb b/lib/maptool/gpx.rb
index b60ea17..80c1381 100644
--- a/lib/maptool/gpx.rb
+++ b/lib/maptool/gpx.rb
@@ -54,6 +54,7 @@ module Maptool
       lines = []
       all_points = []
       times = []
+      extras = []
       trk.each_element("trkseg") do |seg|
         points = []
         seg.each_element("trkpt") do |pt|
@@ -61,6 +62,7 @@ module Maptool
           points << point
           all_points << point
           times << parse_time(child_text(pt, "time"))
+          extras << point_extensions(pt)
         end
         lines << points unless points.empty?
       end
@@ -68,12 +70,31 @@ module Maptool
       {
         "type" => "Feature",
         "geometry" => { "type" => "MultiLineString", "coordinates" => lines },
-        "properties" => { "kind" => "track", "name" => child_text(trk, "name") }
-          .merge(TrackStats.compute(all_points, times: times)),
+        "properties" => { "kind" => "track", "name" => child_text(trk, "name"), "activity_type" => child_text(trk, "type") }
+          .merge(TrackStats.compute(all_points, times: times))
+          .merge("profile" => TrackStats.build_profile(all_points, extras: extras)),
       }
     end
     private_class_method :track_feature
 
+    # Heart rate/cadence/speed live in a device-specific <extensions> block
+    # (usually Garmin's own TrackPointExtension) — matched by local element
+    # name only (`Element#name` already strips the namespace prefix), so
+    # this doesn't care which extension schema a given file actually
+    # declares, as long as it names its elements the same way Garmin's does.
+    def self.point_extensions(point_el)
+      values = {}
+      point_el.elements.each("extensions//*") do |el|
+        case el.name
+        when "hr" then values[:heart_rate_bpm] = el.text&.strip&.to_i
+        when "cad" then values[:cadence_rpm] = el.text&.strip&.to_i
+        when "speed" then values[:speed_mps] = el.text&.strip&.to_f
+        end
+      end
+      values
+    end
+    private_class_method :point_extensions
+
     def self.parse_time(text)
       text && Time.parse(text)
     rescue ArgumentError
diff --git a/lib/maptool/track_stats.rb b/lib/maptool/track_stats.rb
index 6f2b8c7..abd09fd 100644
--- a/lib/maptool/track_stats.rb
+++ b/lib/maptool/track_stats.rb
@@ -27,6 +27,33 @@ module Maptool
       }
     end
 
+    # One entry per coordinate, for the profile chart: cumulative distance
+    # (computed the same way for every format, rather than trusting a
+    # device's own odometer field — keeps a GPX and a FIT file directly
+    # comparable), elevation, and whatever per-point extras (speed/cadence/
+    # heart rate) the caller has, nil where a format/file doesn't carry it.
+    # `extras`: array of hashes parallel to `coordinates`, or shorter/empty.
+    def self.build_profile(coordinates, extras: [])
+      distance = 0.0
+      previous = nil
+
+      coordinates.map.with_index do |(lon, lat, ele), i|
+        distance += haversine(previous[1], previous[0], lat, lon) if previous
+        previous = [lon, lat]
+        extra = extras[i] || {}
+
+        {
+          "distance_meters" => distance.round(1),
+          "elevation_meters" => ele,
+          "speed_mps" => extra[:speed_mps],
+          "cadence_rpm" => extra[:cadence_rpm],
+          "heart_rate_bpm" => extra[:heart_rate_bpm],
+          "lon" => lon,
+          "lat" => lat,
+        }
+      end
+    end
+
     def self.haversine(lat1, lon1, lat2, lon2)
       rad = Math::PI / 180
       dlat = (lat2 - lat1) * rad
diff --git a/public/css/style.css b/public/css/style.css
index 72ef81f..79eb9c9 100644
--- a/public/css/style.css
+++ b/public/css/style.css
@@ -504,3 +504,115 @@ html, body {
   color: #888;
   font-size: 12px;
 }
+
+.profile-panel {
+  position: fixed;
+  left: 52px;
+  right: 0;
+  bottom: 0;
+  max-height: 45vh;
+  display: flex;
+  flex-direction: column;
+  background: #fcfcfb;
+  box-shadow: 0 -2px 8px rgba(0, 0, 0, 0.15);
+  z-index: 10;
+}
+
+.profile-panel[hidden] {
+  display: none;
+}
+
+.profile-panel__header {
+  display: flex;
+  align-items: baseline;
+  gap: 10px;
+  padding: 10px 14px;
+  border-bottom: 1px solid #e1e0d9;
+}
+
+.profile-panel__title {
+  font-size: 14px;
+}
+
+.profile-panel__stats {
+  flex: 1;
+  min-width: 0;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+  color: #52514e;
+  font-size: 13px;
+}
+
+.profile-panel__close {
+  border: none;
+  background: none;
+  font-size: 18px;
+  line-height: 1;
+  padding: 0 4px;
+  cursor: pointer;
+  color: #898781;
+}
+
+.profile-panel__charts {
+  position: relative;
+  overflow-y: auto;
+  padding: 8px 14px 14px;
+}
+
+.profile-chart {
+  padding-top: 8px;
+}
+
+.profile-chart + .profile-chart {
+  border-top: 1px solid #e1e0d9;
+}
+
+.profile-chart__label {
+  font-size: 11px;
+  color: #898781;
+  margin-bottom: 2px;
+}
+
+.profile-chart__unit {
+  font-weight: normal;
+}
+
+.profile-chart__svg {
+  display: block;
+  width: 100%;
+  cursor: crosshair;
+}
+
+.profile-chart__crosshair {
+  stroke: #898781;
+  stroke-width: 1;
+  vector-effect: non-scaling-stroke;
+}
+
+.profile-panel__tooltip {
+  position: absolute;
+  top: 0;
+  z-index: 1;
+  pointer-events: none;
+  background: #0b0b0b;
+  color: #fff;
+  border-radius: 4px;
+  padding: 6px 8px;
+  font-size: 12px;
+  white-space: nowrap;
+  box-shadow: 0 2px 6px rgba(0, 0, 0, 0.25);
+}
+
+.profile-panel__tooltip[hidden] {
+  display: none;
+}
+
+.profile-panel__tooltip-distance {
+  font-weight: 600;
+  margin-bottom: 2px;
+}
+
+.profile-panel__tooltip-label {
+  color: #c3c2b7;
+}
diff --git a/public/js/gpx.js b/public/js/gpx.js
index d98c55a..a7d4d4b 100644
--- a/public/js/gpx.js
+++ b/public/js/gpx.js
@@ -1,6 +1,7 @@
 import { Popup } from "/vendor/maplibre-gl/maplibre-gl.mjs";
 import { GPX_ICON, NEW_FOLDER_ICON, UPLOAD_ICON, WAYPOINT_ICON, TRACK_ICON } from "/js/icons.js";
 import { notifySidePanelOpen, onlyOneSidePanelOpen } from "/js/panels.js";
+import { formatActivityType } from "/js/track_profile.js";
 
 const TREE_URL = "/api/gpx/tree";
 const UPLOAD_URL = "/api/gpx";
@@ -18,8 +19,9 @@ const MOVE_MIME = "application/x-gpx-path";
 // and reorganize by dragging), and toggling their tracks/waypoints on and
 // off the map.
 export class GpxPanelControl {
-  constructor(map) {
+  constructor(map, profilePanel) {
     this._map = map;
+    this._profilePanel = profilePanel;
     this._visible = new Set(); // file paths currently shown on the map
     this._interactiveLayers = new Set(); // point layer ids with click/hover wired up
 
@@ -331,9 +333,12 @@ export class GpxPanelControl {
     });
   }
 
-  // Hover rather than click: unlike a waypoint, a track's properties
-  // (distance, elevation gain, duration) describe the whole line, not
-  // whatever point along it happens to get clicked.
+  // Hover shows a quick summary (unlike a waypoint popup, which is
+  // click-triggered — a track's summary describes the whole line, not
+  // whatever point along it happens to get hovered, so there's no single
+  // right anchor point worth waiting for a click on). Click opens the full
+  // profile panel, which does need the click gesture to avoid flashing
+  // open on every casual hover.
   _registerLineInteractivity(layerId) {
     if (this._interactiveLayers.has(layerId)) return;
     this._interactiveLayers.add(layerId);
@@ -353,6 +358,10 @@ export class GpxPanelControl {
       popup?.remove();
       popup = null;
     });
+    this._map.on("click", layerId, (event) => {
+      const feature = event.features[0];
+      if (feature) this._profilePanel?.show(feature.properties);
+    });
   }
 
   _removeLayers(path) {
@@ -488,15 +497,17 @@ function popupHtml({ name, description, time }) {
 }
 
 // properties come straight from an uploaded GPX/FIT file — untrusted input.
-function trackPopupHtml({ name, distance_meters, elevation_gain_meters, duration_secs }) {
+function trackPopupHtml({ name, activity_type, distance_meters, elevation_gain_meters, duration_secs }) {
   const parts = [];
   if (name) parts.push(`<strong>${escapeHtml(name)}</strong>`);
 
   const stats = [];
+  if (activity_type) stats.push(escapeHtml(formatActivityType(activity_type)));
   if (typeof distance_meters === "number") stats.push(`${(distance_meters / 1000).toFixed(1)} km`);
   if (typeof elevation_gain_meters === "number") stats.push(`↑ ${Math.round(elevation_gain_meters)} m`);
   if (typeof duration_secs === "number") stats.push(formatDuration(duration_secs));
   if (stats.length > 0) parts.push(`<p>${stats.join(" · ")}</p>`);
+  parts.push(`<p class="gpx-popup__time">Click for the full profile</p>`);
 
   return parts.length > 0 ? parts.join("") : "<em>No details</em>";
 }
diff --git a/public/js/map.js b/public/js/map.js
index 816fb3c..1a55f90 100644
--- a/public/js/map.js
+++ b/public/js/map.js
@@ -8,6 +8,7 @@ import { RadarControl } from "/js/radar.js";
 import { GpxPanelControl } from "/js/gpx.js";
 import { GnssControl } from "/js/gnss.js";
 import { LiveTrackPanelControl } from "/js/livetrack.js";
+import { TrackProfilePanel } from "/js/track_profile.js";
 import { LAYERS_ICON } from "/js/icons.js";
 import { notifySidePanelOpen, onlyOneSidePanelOpen } from "/js/panels.js";
 
@@ -125,7 +126,9 @@ const layerToggle = new LayerToggleControl(applyStyle);
 layerToggle.mount(sidebar);
 layerToggle.setActive("online");
 
-new GpxPanelControl(map).mount(sidebar);
+const profilePanel = new TrackProfilePanel(map);
+profilePanel.mount();
+new GpxPanelControl(map, profilePanel).mount(sidebar);
 new RadarControl(map).mount(sidebar);
 new GnssControl(map).mount(sidebar);
 new LiveTrackPanelControl(map).mount(sidebar);
diff --git a/public/js/track_profile.js b/public/js/track_profile.js
new file mode 100644
index 0000000..5ab796e
--- /dev/null
+++ b/public/js/track_profile.js
@@ -0,0 +1,218 @@
+import { Marker } from "/vendor/maplibre-gl/maplibre-gl.mjs";
+
+// Small-multiples profile chart: one row per metric the track actually has
+// (elevation always, speed/cadence/heart rate only when present — plenty of
+// GPX files have none of those), sharing one x-axis (distance) and one
+// crosshair. Elevation/speed/cadence/heart rate live on wildly different
+// scales, so this is deliberately several single-series charts stacked
+// rather than one chart with several y-axes (see dataviz skill: no
+// dual-axis charts).
+//
+// SVG viewBox is a fixed 1000-unit-wide coordinate space (not real pixels)
+// stretched to the container via CSS — mouse interaction converts
+// clientX through the container's current bounding rect on every move, so
+// this stays correct across container width without redrawing, but a
+// browser window resize while the panel is open won't reflow the drawn
+// paths until it's reopened. Acceptable for a detail panel that's normally
+// open briefly; add a resize listener if that turns out to matter.
+const VIEWBOX_WIDTH = 1000;
+
+const SERIES = [
+  { key: "elevation_meters", label: "Elevation", unit: "m", color: "#2a78d6", height: 110, area: true },
+  { key: "speed_kmh", label: "Speed", unit: "km/h", color: "#1baf7a", height: 70, area: false },
+  { key: "cadence_rpm", label: "Cadence", unit: "rpm", color: "#eda100", height: 70, area: false },
+  { key: "heart_rate_bpm", label: "Heart rate", unit: "bpm", color: "#e34948", height: 70, area: false },
+];
+
+export class TrackProfilePanel {
+  constructor(map) {
+    this._map = map;
+    this._profile = null;
+    this._marker = new Marker({ color: "#7209b7" });
+  }
+
+  mount() {
+    this._panel = document.getElementById("profile-panel");
+    this._title = this._panel.querySelector(".profile-panel__title");
+    this._stats = this._panel.querySelector(".profile-panel__stats");
+    this._chartsContainer = this._panel.querySelector(".profile-panel__charts");
+    this._panel.querySelector(".profile-panel__close").addEventListener("click", () => this.hide());
+  }
+
+  show(properties) {
+    const profile = properties.profile;
+    if (!profile || profile.length === 0) return;
+
+    this._profile = profile.map((point) => ({ ...point, speed_kmh: typeof point.speed_mps === "number" ? point.speed_mps * 3.6 : null }));
+    this._maxDistance = this._profile.at(-1).distance_meters || 1;
+
+    this._title.textContent = properties.name || "Track";
+    this._stats.textContent = statsText(properties);
+
+    this._chartsContainer.innerHTML = "";
+    this._tooltip = document.createElement("div");
+    this._tooltip.className = "profile-panel__tooltip";
+    this._tooltip.hidden = true;
+    this._chartsContainer.appendChild(this._tooltip);
+
+    this._activeSeries = SERIES.filter((s) => this._profile.some((p) => typeof p[s.key] === "number"));
+    this._activeSeries.forEach((series) => this._chartsContainer.appendChild(this._renderChart(series)));
+
+    this._chartsContainer.addEventListener("pointermove", this._onPointerMove);
+    this._chartsContainer.addEventListener("pointerleave", this._onPointerLeave);
+
+    this._panel.hidden = false;
+  }
+
+  hide() {
+    this._panel.hidden = true;
+    this._chartsContainer.removeEventListener("pointermove", this._onPointerMove);
+    this._chartsContainer.removeEventListener("pointerleave", this._onPointerLeave);
+    this._marker.remove();
+  }
+
+  _renderChart(series) {
+    const values = this._profile.map((p) => p[series.key]).filter((v) => typeof v === "number");
+    const min = Math.min(...values);
+    const max = Math.max(...values);
+    const range = max - min || 1;
+
+    const toX = (d) => (d / this._maxDistance) * VIEWBOX_WIDTH;
+    const toY = (v) => series.height - 6 - ((v - min) / range) * (series.height - 12);
+
+    const points = this._profile
+      .map((p) => (typeof p[series.key] === "number" ? [toX(p.distance_meters), toY(p[series.key])] : null))
+      .filter(Boolean);
+    const linePath = points.map(([x, y], i) => `${i === 0 ? "M" : "L"}${x.toFixed(1)},${y.toFixed(1)}`).join(" ");
+    const areaPath = series.area && points.length > 0
+      ? `${linePath} L${points.at(-1)[0].toFixed(1)},${series.height} L0,${series.height} Z`
+      : "";
+
+    const wrapper = document.createElement("div");
+    wrapper.className = "profile-chart";
+    wrapper.innerHTML = `
+      <div class="profile-chart__label">${escapeHtml(series.label)} <span class="profile-chart__unit">(${escapeHtml(series.unit)})</span></div>
+      <svg viewBox="0 0 ${VIEWBOX_WIDTH} ${series.height}" preserveAspectRatio="none" class="profile-chart__svg" style="height:${series.height}px">
+        ${areaPath ? `<path d="${areaPath}" fill="${series.color}" fill-opacity="0.15" stroke="none"></path>` : ""}
+        <path d="${linePath}" fill="none" stroke="${series.color}" stroke-width="2" vector-effect="non-scaling-stroke"></path>
+        <line class="profile-chart__crosshair" x1="0" x2="0" y1="0" y2="${series.height}" hidden></line>
+        <circle class="profile-chart__dot" r="4" fill="${series.color}" stroke="#fff" stroke-width="1.5" hidden></circle>
+      </svg>
+    `;
+    wrapper.dataset.min = min;
+    wrapper.dataset.max = max;
+    return wrapper;
+  }
+
+  // Bound once (arrow fields, not prototype methods) so add/removeEventListener see the same reference.
+  _onPointerMove = (event) => {
+    const rect = this._chartsContainer.getBoundingClientRect();
+    const fraction = Math.min(1, Math.max(0, (event.clientX - rect.left) / rect.width));
+    const targetDistance = fraction * this._maxDistance;
+
+    const index = nearestIndex(this._profile, targetDistance);
+    const point = this._profile[index];
+    this._updateCrosshair(point);
+    this._updateTooltip(point, event);
+    this._marker.setLngLat([point.lon, point.lat]).addTo(this._map);
+  };
+
+  _onPointerLeave = () => {
+    this._tooltip.hidden = true;
+    this._chartsContainer.querySelectorAll(".profile-chart__crosshair, .profile-chart__dot").forEach((el) => (el.hidden = true));
+    this._marker.remove();
+  };
+
+  _updateCrosshair(point) {
+    const x = (point.distance_meters / this._maxDistance) * VIEWBOX_WIDTH;
+    this._chartsContainer.querySelectorAll(".profile-chart").forEach((wrapper, i) => {
+      const series = this._activeSeries[i];
+      const value = point[series.key];
+      const svg = wrapper.querySelector("svg");
+      const crosshair = wrapper.querySelector(".profile-chart__crosshair");
+      const dot = wrapper.querySelector(".profile-chart__dot");
+      crosshair.setAttribute("x1", x.toFixed(1));
+      crosshair.setAttribute("x2", x.toFixed(1));
+      crosshair.hidden = false;
+      if (typeof value === "number") {
+        const min = Number(wrapper.dataset.min);
+        const max = Number(wrapper.dataset.max);
+        const range = max - min || 1;
+        const y = series.height - 6 - ((value - min) / range) * (series.height - 12);
+        dot.setAttribute("cx", x.toFixed(1));
+        dot.setAttribute("cy", y.toFixed(1));
+        dot.hidden = false;
+      } else {
+        dot.hidden = true;
+      }
+      void svg; // svg itself needs no direct update, its children were mutated above
+    });
+  }
+
+  _updateTooltip(point, event) {
+    const rows = this._activeSeries
+      .filter((s) => typeof point[s.key] === "number")
+      .map((s) => `<div><span class="profile-panel__tooltip-label">${escapeHtml(s.label)}</span> <strong>${formatValue(point[s.key], s)}</strong></div>`)
+      .join("");
+    this._tooltip.innerHTML = `<div class="profile-panel__tooltip-distance">${(point.distance_meters / 1000).toFixed(2)} km</div>${rows}`;
+    this._tooltip.hidden = false;
+
+    const containerRect = this._chartsContainer.getBoundingClientRect();
+    const left = Math.min(event.clientX - containerRect.left + 12, containerRect.width - this._tooltip.offsetWidth - 8);
+    this._tooltip.style.left = `${Math.max(8, left)}px`;
+  }
+}
+
+function nearestIndex(profile, targetDistance) {
+  // Distances are monotonically non-decreasing (see TrackStats.build_profile),
+  // so a binary search would work too — linear is simpler and profiles here
+  // top out in the low thousands of points, not worth the complexity.
+  let closest = 0;
+  let closestDiff = Infinity;
+  profile.forEach((p, i) => {
+    const diff = Math.abs(p.distance_meters - targetDistance);
+    if (diff < closestDiff) {
+      closestDiff = diff;
+      closest = i;
+    }
+  });
+  return closest;
+}
+
+function formatValue(value, series) {
+  if (series.key === "elevation_meters") return `${Math.round(value)} ${series.unit}`;
+  if (series.key === "speed_kmh") return `${value.toFixed(1)} ${series.unit}`;
+  return `${Math.round(value)} ${series.unit}`;
+}
+
+function statsText({ activity_type, distance_meters, elevation_gain_meters, duration_secs }) {
+  const parts = [];
+  if (activity_type) parts.push(formatActivityType(activity_type));
+  if (typeof distance_meters === "number") parts.push(`${(distance_meters / 1000).toFixed(1)} km`);
+  if (typeof elevation_gain_meters === "number") parts.push(`↑ ${Math.round(elevation_gain_meters)} m`);
+  if (typeof duration_secs === "number") parts.push(formatDuration(duration_secs));
+  return parts.join(" · ");
+}
+
+// FIT gives snake_case ("cross_country_skiing"); GPX's free-text <type> can
+// be anything a device/app chose to write ("VirtualRide", "running", ...) —
+// this reads reasonably for both without needing to know which format the
+// track came from.
+export function formatActivityType(text) {
+  return text
+    .split("_")
+    .map((word) => word.charAt(0).toUpperCase() + word.slice(1))
+    .join(" ");
+}
+
+function formatDuration(totalSeconds) {
+  const hours = Math.floor(totalSeconds / 3600);
+  const minutes = Math.floor((totalSeconds % 3600) / 60);
+  return hours > 0 ? `${hours}h ${minutes}m` : `${minutes}m`;
+}
+
+function escapeHtml(text) {
+  const div = document.createElement("div");
+  div.textContent = text;
+  return div.innerHTML;
+}
diff --git a/test/fixtures/sample.gpx b/test/fixtures/sample.gpx
index 0ad720e..ae444ee 100644
--- a/test/fixtures/sample.gpx
+++ b/test/fixtures/sample.gpx
@@ -8,14 +8,27 @@
   </wpt>
   <trk>
     <name>Morning Loop</name>
+    <type>running</type>
     <trkseg>
       <trkpt lat="48.1" lon="17.2">
         <ele>200</ele>
         <time>2026-01-01T09:00:00Z</time>
+        <extensions>
+          <gpxtpx:TrackPointExtension xmlns:gpxtpx="http://www.garmin.com/xmlschemas/TrackPointExtension/v1">
+            <gpxtpx:hr>140</gpxtpx:hr>
+            <gpxtpx:cad>80</gpxtpx:cad>
+          </gpxtpx:TrackPointExtension>
+        </extensions>
       </trkpt>
       <trkpt lat="48.101" lon="17.201">
         <ele>250</ele>
         <time>2026-01-01T09:10:00Z</time>
+        <extensions>
+          <gpxtpx:TrackPointExtension xmlns:gpxtpx="http://www.garmin.com/xmlschemas/TrackPointExtension/v1">
+            <gpxtpx:hr>155</gpxtpx:hr>
+            <gpxtpx:cad>84</gpxtpx:cad>
+          </gpxtpx:TrackPointExtension>
+        </extensions>
       </trkpt>
       <trkpt lat="48.102" lon="17.202">
         <ele>230</ele>
diff --git a/test/test_fit.rb b/test/test_fit.rb
index 9ce6678..52e8133 100644
--- a/test/test_fit.rb
+++ b/test/test_fit.rb
@@ -57,4 +57,68 @@ class FitTest < Minitest::Test
 
     assert_raises(Maptool::Fit::ParseError) { Maptool::Fit.to_geojson(path) }
   end
+
+  # A second, richer fixture (session message with a sport enum, record
+  # messages carrying heart_rate/cadence/speed too) — kept separate from
+  # build_fit/write_fit above so those stay a minimal, easy-to-read
+  # position-only case.
+  def build_activity_fit(records, sport: nil)
+    body = +""
+
+    if sport
+      session_definition = [0, 0].pack("CC") + [18].pack("S<") + [1].pack("C") + [5, 1, 0x00].pack("C3")
+      body << [0b01000001].pack("C") << session_definition
+      body << [0b00000001].pack("C") << [sport].pack("C")
+    end
+
+    record_definition = [0, 0].pack("CC") + [20].pack("S<") + [5].pack("C") +
+                         [0, 4, 0x85].pack("C3") + [1, 4, 0x85].pack("C3") +
+                         [3, 1, 0x02].pack("C3") + [4, 1, 0x02].pack("C3") + [6, 2, 0x84].pack("C3")
+    body << [0b01000000].pack("C") << record_definition
+
+    records.each do |r|
+      body << [0b00000000].pack("C") << le32(r[:lat]) << le32(r[:lon])
+      body << [r[:heart_rate] || 0xFF].pack("C") << [r[:cadence] || 0xFF].pack("C")
+      speed_raw = r[:speed_mps] ? (r[:speed_mps] * 1000).round : 0xFFFF
+      body << [speed_raw].pack("S<")
+    end
+
+    header = [12, 16, 0, 0].pack("C2S<") + le32(body.bytesize) + ".FIT"
+    header + body + "\x00\x00"
+  end
+
+  def write_activity_fit(records, sport: nil)
+    path = File.join(Dir.mktmpdir, "activity.fit")
+    File.binwrite(path, build_activity_fit(records, sport: sport))
+    path
+  end
+
+  def test_activity_type_comes_from_the_session_messages_sport_enum
+    path = write_activity_fit([{ lat: 100_000_000, lon: 200_000_000 }], sport: 2)
+    geojson = Maptool::Fit.to_geojson(path)
+
+    assert_equal "cycling", geojson["features"][0]["properties"]["activity_type"]
+  end
+
+  def test_activity_type_is_nil_without_a_session_message
+    path = write_activity_fit([{ lat: 100_000_000, lon: 200_000_000 }])
+    geojson = Maptool::Fit.to_geojson(path)
+
+    assert_nil geojson["features"][0]["properties"]["activity_type"]
+  end
+
+  def test_profile_carries_heart_rate_cadence_and_speed_treating_0xff_as_absent
+    path = write_activity_fit([
+      { lat: 100_000_000, lon: 200_000_000, heart_rate: 140, cadence: 80, speed_mps: 3.5 },
+      { lat: 100_000_100, lon: 200_000_100 }, # no extras -> 0xFF/0xFFFF sentinels
+    ])
+
+    profile = Maptool::Fit.to_geojson(path)["features"][0]["properties"]["profile"]
+
+    assert_equal 140, profile[0]["heart_rate_bpm"]
+    assert_equal 80, profile[0]["cadence_rpm"]
+    assert_in_delta 3.5, profile[0]["speed_mps"]
+    assert_nil profile[1]["heart_rate_bpm"]
+    assert_nil profile[1]["speed_mps"]
+  end
 end
diff --git a/test/test_gpx.rb b/test/test_gpx.rb
index e71cb25..1f40a94 100644
--- a/test/test_gpx.rb
+++ b/test/test_gpx.rb
@@ -23,11 +23,24 @@ class GpxTest < Minitest::Test
     assert_equal "MultiLineString", track["geometry"]["type"]
     assert_equal 3, track["geometry"]["coordinates"][0].size
     assert_equal "Morning Loop", track["properties"]["name"]
+    assert_equal "running", track["properties"]["activity_type"]
     assert_operator track["properties"]["distance_meters"], :>, 0
     assert_equal 50.0, track["properties"]["elevation_gain_meters"], "200->250 is the only gain, 250->230 descent not subtracted"
     assert_equal 1200, track["properties"]["duration_secs"]
   end
 
+  def test_track_profile_carries_extension_fields_and_tolerates_points_without_them
+    geojson = Maptool::Gpx.to_geojson(fixture_path("sample.gpx"))
+    profile = geojson["features"].find { |f| f["properties"]["kind"] == "track" }["properties"]["profile"]
+
+    assert_equal 3, profile.size
+    assert_equal 140, profile[0]["heart_rate_bpm"]
+    assert_equal 84, profile[1]["cadence_rpm"]
+    assert_nil profile[2]["heart_rate_bpm"], "third point has no <extensions>"
+    assert_equal 0.0, profile[0]["distance_meters"]
+    assert_equal [17.2, 48.1], [profile[0]["lon"], profile[0]["lat"]]
+  end
+
   def test_invalid_xml_raises_parse_error
     path = File.join(Dir.mktmpdir, "bad.gpx")
     File.write(path, "<gpx><trk unclosed>")
diff --git a/test/test_track_stats.rb b/test/test_track_stats.rb
index 1e04a3a..7750272 100644
--- a/test/test_track_stats.rb
+++ b/test/test_track_stats.rb
@@ -32,4 +32,26 @@ class TrackStatsTest < Minitest::Test
     stats = Maptool::TrackStats.compute([[17.0, 48.0]])
     assert_equal 0.0, stats["distance_meters"]
   end
+
+  def test_build_profile_has_cumulative_distance_elevation_and_extras
+    points = [[17.0, 48.0, 100], [17.001, 48.0, 150]]
+    extras = [{ heart_rate_bpm: 120 }, { heart_rate_bpm: 130, cadence_rpm: 80 }]
+
+    profile = Maptool::TrackStats.build_profile(points, extras: extras)
+
+    assert_equal 2, profile.size
+    assert_equal 0.0, profile[0]["distance_meters"]
+    assert_equal 100, profile[0]["elevation_meters"]
+    assert_equal 120, profile[0]["heart_rate_bpm"]
+    assert_nil profile[0]["cadence_rpm"]
+    assert_operator profile[1]["distance_meters"], :>, 0
+    assert_equal 80, profile[1]["cadence_rpm"]
+    assert_equal [17.001, 48.0], [profile[1]["lon"], profile[1]["lat"]]
+  end
+
+  def test_build_profile_extras_default_to_nil_when_shorter_than_coordinates
+    profile = Maptool::TrackStats.build_profile([[17.0, 48.0], [17.001, 48.0]], extras: [])
+    assert_nil profile[0]["heart_rate_bpm"]
+    assert_nil profile[1]["speed_mps"]
+  end
 end
diff --git a/views/index.erb b/views/index.erb
index 712b889..8483197 100644
--- a/views/index.erb
+++ b/views/index.erb
@@ -17,6 +17,15 @@
   </div>
 </div>
 
+<div id="profile-panel" class="profile-panel" hidden>
+  <div class="profile-panel__header">
+    <strong class="profile-panel__title"></strong>
+    <span class="profile-panel__stats"></span>
+    <button type="button" class="profile-panel__close" aria-label="Close">&times;</button>
+  </div>
+  <div class="profile-panel__charts"></div>
+</div>
+
 <div id="basemap-panel" class="basemap-panel" hidden>
   <div class="basemap-panel__header">
     <strong>Base map</strong>
diff --git a/views/layout.erb b/views/layout.erb
index 076a307..b8e184c 100644
--- a/views/layout.erb
+++ b/views/layout.erb
@@ -25,7 +25,8 @@
         "/js/icons.js": "/js/icons.js?v=<%= ASSET_VERSION %>",
         "/js/livetrack.js": "/js/livetrack.js?v=<%= ASSET_VERSION %>",
         "/js/panels.js": "/js/panels.js?v=<%= ASSET_VERSION %>",
-        "/js/radar.js": "/js/radar.js?v=<%= ASSET_VERSION %>"
+        "/js/radar.js": "/js/radar.js?v=<%= ASSET_VERSION %>",
+        "/js/track_profile.js": "/js/track_profile.js?v=<%= ASSET_VERSION %>"
       }
     }
   </script>